Related
Java has a convenient split method:
String str = "The quick brown fox";
String[] results = str.split(" ");
Is there an easy way to do this in C++?
The Boost tokenizer class can make this sort of thing quite simple:
#include <iostream>
#include <string>
#include <boost/foreach.hpp>
#include <boost/tokenizer.hpp>
using namespace std;
using namespace boost;
int main(int, char**)
{
string text = "token, test string";
char_separator<char> sep(", ");
tokenizer< char_separator<char> > tokens(text, sep);
BOOST_FOREACH (const string& t, tokens) {
cout << t << "." << endl;
}
}
Updated for C++11:
#include <iostream>
#include <string>
#include <boost/tokenizer.hpp>
using namespace std;
using namespace boost;
int main(int, char**)
{
string text = "token, test string";
char_separator<char> sep(", ");
tokenizer<char_separator<char>> tokens(text, sep);
for (const auto& t : tokens) {
cout << t << "." << endl;
}
}
Here's a real simple one:
#include <vector>
#include <string>
using namespace std;
vector<string> split(const char *str, char c = ' ')
{
vector<string> result;
do
{
const char *begin = str;
while(*str != c && *str)
str++;
result.push_back(string(begin, str));
} while (0 != *str++);
return result;
}
C++ standard library algorithms are pretty universally based around iterators rather than concrete containers. Unfortunately this makes it hard to provide a Java-like split function in the C++ standard library, even though nobody argues that this would be convenient. But what would its return type be? std::vector<std::basic_string<…>>? Maybe, but then we’re forced to perform (potentially redundant and costly) allocations.
Instead, C++ offers a plethora of ways to split strings based on arbitrarily complex delimiters, but none of them is encapsulated as nicely as in other languages. The numerous ways fill whole blog posts.
At its simplest, you could iterate using std::string::find until you hit std::string::npos, and extract the contents using std::string::substr.
A more fluid (and idiomatic, but basic) version for splitting on whitespace would use a std::istringstream:
auto iss = std::istringstream{"The quick brown fox"};
auto str = std::string{};
while (iss >> str) {
process(str);
}
Using std::istream_iterators, the contents of the string stream could also be copied into a vector using its iterator range constructor.
Multiple libraries (such as Boost.Tokenizer) offer specific tokenisers.
More advanced splitting require regular expressions. C++ provides the std::regex_token_iterator for this purpose in particular:
auto const str = "The quick brown fox"s;
auto const re = std::regex{R"(\s+)"};
auto const vec = std::vector<std::string>(
std::sregex_token_iterator{begin(str), end(str), re, -1},
std::sregex_token_iterator{}
);
Another quick way is to use getline. Something like:
stringstream ss("bla bla");
string s;
while (getline(ss, s, ' ')) {
cout << s << endl;
}
If you want, you can make a simple split() method returning a vector<string>, which is
really useful.
Use strtok. In my opinion, there isn't a need to build a class around tokenizing unless strtok doesn't provide you with what you need. It might not, but in 15+ years of writing various parsing code in C and C++, I've always used strtok. Here is an example
char myString[] = "The quick brown fox";
char *p = strtok(myString, " ");
while (p) {
printf ("Token: %s\n", p);
p = strtok(NULL, " ");
}
A few caveats (which might not suit your needs). The string is "destroyed" in the process, meaning that EOS characters are placed inline in the delimter spots. Correct usage might require you to make a non-const version of the string. You can also change the list of delimiters mid parse.
In my own opinion, the above code is far simpler and easier to use than writing a separate class for it. To me, this is one of those functions that the language provides and it does it well and cleanly. It's simply a "C based" solution. It's appropriate, it's easy, and you don't have to write a lot of extra code :-)
You can use streams, iterators, and the copy algorithm to do this fairly directly.
#include <string>
#include <vector>
#include <iostream>
#include <istream>
#include <ostream>
#include <iterator>
#include <sstream>
#include <algorithm>
int main()
{
std::string str = "The quick brown fox";
// construct a stream from the string
std::stringstream strstr(str);
// use stream iterators to copy the stream to the vector as whitespace separated strings
std::istream_iterator<std::string> it(strstr);
std::istream_iterator<std::string> end;
std::vector<std::string> results(it, end);
// send the vector to stdout.
std::ostream_iterator<std::string> oit(std::cout);
std::copy(results.begin(), results.end(), oit);
}
A solution using regex_token_iterators:
#include <iostream>
#include <regex>
#include <string>
using namespace std;
int main()
{
string str("The quick brown fox");
regex reg("\\s+");
sregex_token_iterator iter(str.begin(), str.end(), reg, -1);
sregex_token_iterator end;
vector<string> vec(iter, end);
for (auto a : vec)
{
cout << a << endl;
}
}
No offense folks, but for such a simple problem, you are making things way too complicated. There are a lot of reasons to use Boost. But for something this simple, it's like hitting a fly with a 20# sledge.
void
split( vector<string> & theStringVector, /* Altered/returned value */
const string & theString,
const string & theDelimiter)
{
UASSERT( theDelimiter.size(), >, 0); // My own ASSERT macro.
size_t start = 0, end = 0;
while ( end != string::npos)
{
end = theString.find( theDelimiter, start);
// If at end, use length=maxLength. Else use length=end-start.
theStringVector.push_back( theString.substr( start,
(end == string::npos) ? string::npos : end - start));
// If at end, use start=maxSize. Else use start=end+delimiter.
start = ( ( end > (string::npos - theDelimiter.size()) )
? string::npos : end + theDelimiter.size());
}
}
For example (for Doug's case),
#define SHOW(I,X) cout << "[" << (I) << "]\t " # X " = \"" << (X) << "\"" << endl
int
main()
{
vector<string> v;
split( v, "A:PEP:909:Inventory Item", ":" );
for (unsigned int i = 0; i < v.size(); i++)
SHOW( i, v[i] );
}
And yes, we could have split() return a new vector rather than passing one in. It's trivial to wrap and overload. But depending on what I'm doing, I often find it better to re-use pre-existing objects rather than always creating new ones. (Just as long as I don't forget to empty the vector in between!)
Reference: http://www.cplusplus.com/reference/string/string/.
(I was originally writing a response to Doug's question: C++ Strings Modifying and Extracting based on Separators (closed). But since Martin York closed that question with a pointer over here... I'll just generalize my code.)
Boost has a strong split function: boost::algorithm::split.
Sample program:
#include <vector>
#include <boost/algorithm/string.hpp>
int main() {
auto s = "a,b, c ,,e,f,";
std::vector<std::string> fields;
boost::split(fields, s, boost::is_any_of(","));
for (const auto& field : fields)
std::cout << "\"" << field << "\"\n";
return 0;
}
Output:
"a"
"b"
" c "
""
"e"
"f"
""
This is a simple STL-only solution (~5 lines!) using std::find and std::find_first_not_of that handles repetitions of the delimiter (like spaces or periods for instance), as well leading and trailing delimiters:
#include <string>
#include <vector>
void tokenize(std::string str, std::vector<string> &token_v){
size_t start = str.find_first_not_of(DELIMITER), end=start;
while (start != std::string::npos){
// Find next occurence of delimiter
end = str.find(DELIMITER, start);
// Push back the token found into vector
token_v.push_back(str.substr(start, end-start));
// Skip all occurences of the delimiter to find new start
start = str.find_first_not_of(DELIMITER, end);
}
}
Try it out live!
I know you asked for a C++ solution, but you might consider this helpful:
Qt
#include <QString>
...
QString str = "The quick brown fox";
QStringList results = str.split(" ");
The advantage over Boost in this example is that it's a direct one to one mapping to your post's code.
See more at Qt documentation
Here is a sample tokenizer class that might do what you want
//Header file
class Tokenizer
{
public:
static const std::string DELIMITERS;
Tokenizer(const std::string& str);
Tokenizer(const std::string& str, const std::string& delimiters);
bool NextToken();
bool NextToken(const std::string& delimiters);
const std::string GetToken() const;
void Reset();
protected:
size_t m_offset;
const std::string m_string;
std::string m_token;
std::string m_delimiters;
};
//CPP file
const std::string Tokenizer::DELIMITERS(" \t\n\r");
Tokenizer::Tokenizer(const std::string& s) :
m_string(s),
m_offset(0),
m_delimiters(DELIMITERS) {}
Tokenizer::Tokenizer(const std::string& s, const std::string& delimiters) :
m_string(s),
m_offset(0),
m_delimiters(delimiters) {}
bool Tokenizer::NextToken()
{
return NextToken(m_delimiters);
}
bool Tokenizer::NextToken(const std::string& delimiters)
{
size_t i = m_string.find_first_not_of(delimiters, m_offset);
if (std::string::npos == i)
{
m_offset = m_string.length();
return false;
}
size_t j = m_string.find_first_of(delimiters, i);
if (std::string::npos == j)
{
m_token = m_string.substr(i);
m_offset = m_string.length();
return true;
}
m_token = m_string.substr(i, j - i);
m_offset = j;
return true;
}
Example:
std::vector <std::string> v;
Tokenizer s("split this string", " ");
while (s.NextToken())
{
v.push_back(s.GetToken());
}
pystring is a small library which implements a bunch of Python's string functions, including the split method:
#include <string>
#include <vector>
#include "pystring.h"
std::vector<std::string> chunks;
pystring::split("this string", chunks);
// also can specify a separator
pystring::split("this-string", chunks, "-");
I posted this answer for similar question.
Don't reinvent the wheel. I've used a number of libraries and the fastest and most flexible I have come across is: C++ String Toolkit Library.
Here is an example of how to use it that I've posted else where on the stackoverflow.
#include <iostream>
#include <vector>
#include <string>
#include <strtk.hpp>
const char *whitespace = " \t\r\n\f";
const char *whitespace_and_punctuation = " \t\r\n\f;,=";
int main()
{
{ // normal parsing of a string into a vector of strings
std::string s("Somewhere down the road");
std::vector<std::string> result;
if( strtk::parse( s, whitespace, result ) )
{
for(size_t i = 0; i < result.size(); ++i )
std::cout << result[i] << std::endl;
}
}
{ // parsing a string into a vector of floats with other separators
// besides spaces
std::string s("3.0, 3.14; 4.0");
std::vector<float> values;
if( strtk::parse( s, whitespace_and_punctuation, values ) )
{
for(size_t i = 0; i < values.size(); ++i )
std::cout << values[i] << std::endl;
}
}
{ // parsing a string into specific variables
std::string s("angle = 45; radius = 9.9");
std::string w1, w2;
float v1, v2;
if( strtk::parse( s, whitespace_and_punctuation, w1, v1, w2, v2) )
{
std::cout << "word " << w1 << ", value " << v1 << std::endl;
std::cout << "word " << w2 << ", value " << v2 << std::endl;
}
}
return 0;
}
Adam Pierce's answer provides an hand-spun tokenizer taking in a const char*. It's a bit more problematic to do with iterators because incrementing a string's end iterator is undefined. That said, given string str{ "The quick brown fox" } we can certainly accomplish this:
auto start = find(cbegin(str), cend(str), ' ');
vector<string> tokens{ string(cbegin(str), start) };
while (start != cend(str)) {
const auto finish = find(++start, cend(str), ' ');
tokens.push_back(string(start, finish));
start = finish;
}
Live Example
If you're looking to abstract complexity by using standard functionality, as On Freund suggests strtok is a simple option:
vector<string> tokens;
for (auto i = strtok(data(str), " "); i != nullptr; i = strtok(nullptr, " ")) tokens.push_back(i);
If you don't have access to C++17 you'll need to substitute data(str) as in this example: http://ideone.com/8kAGoa
Though not demonstrated in the example, strtok need not use the same delimiter for each token. Along with this advantage though, there are several drawbacks:
strtok cannot be used on multiple strings at the same time: Either a nullptr must be passed to continue tokenizing the current string or a new char* to tokenize must be passed (there are some non-standard implementations which do support this however, such as: strtok_s)
For the same reason strtok cannot be used on multiple threads simultaneously (this may however be implementation defined, for example: Visual Studio's implementation is thread safe)
Calling strtok modifies the string it is operating on, so it cannot be used on const strings, const char*s, or literal strings, to tokenize any of these with strtok or to operate on a string who's contents need to be preserved, str would have to be copied, then the copy could be operated on
c++20 provides us with split_view to tokenize strings, in a non-destructive manner: https://topanswers.xyz/cplusplus?q=749#a874
The previous methods cannot generate a tokenized vector in-place, meaning without abstracting them into a helper function they cannot initialize const vector<string> tokens. That functionality and the ability to accept any white-space delimiter can be harnessed using an istream_iterator. For example given: const string str{ "The quick \tbrown \nfox" } we can do this:
istringstream is{ str };
const vector<string> tokens{ istream_iterator<string>(is), istream_iterator<string>() };
Live Example
The required construction of an istringstream for this option has far greater cost than the previous 2 options, however this cost is typically hidden in the expense of string allocation.
If none of the above options are flexable enough for your tokenization needs, the most flexible option is using a regex_token_iterator of course with this flexibility comes greater expense, but again this is likely hidden in the string allocation cost. Say for example we want to tokenize based on non-escaped commas, also eating white-space, given the following input: const string str{ "The ,qu\\,ick ,\tbrown, fox" } we can do this:
const regex re{ "\\s*((?:[^\\\\,]|\\\\.)*?)\\s*(?:,|$)" };
const vector<string> tokens{ sregex_token_iterator(cbegin(str), cend(str), re, 1), sregex_token_iterator() };
Live Example
Check this example. It might help you..
#include <iostream>
#include <sstream>
using namespace std;
int main ()
{
string tmps;
istringstream is ("the dellimiter is the space");
while (is.good ()) {
is >> tmps;
cout << tmps << "\n";
}
return 0;
}
If you're using C++ ranges - the full ranges-v3 library, not the limited functionality accepted into C++20 - you could do it this way:
auto results = str | ranges::views::tokenize(" ",1);
... and this is lazily-evaluated. You can alternatively set a vector to this range:
auto results = str | ranges::views::tokenize(" ",1) | ranges::to<std::vector>();
this will take O(m) space and O(n) time if str has n characters making up m words.
See also the library's own tokenization example, here.
MFC/ATL has a very nice tokenizer. From MSDN:
CAtlString str( "%First Second#Third" );
CAtlString resToken;
int curPos= 0;
resToken= str.Tokenize("% #",curPos);
while (resToken != "")
{
printf("Resulting token: %s\n", resToken);
resToken= str.Tokenize("% #",curPos);
};
Output
Resulting Token: First
Resulting Token: Second
Resulting Token: Third
If you're willing to use C, you can use the strtok function. You should pay attention to multi-threading issues when using it.
For simple stuff I just use the following:
unsigned TokenizeString(const std::string& i_source,
const std::string& i_seperators,
bool i_discard_empty_tokens,
std::vector<std::string>& o_tokens)
{
unsigned prev_pos = 0;
unsigned pos = 0;
unsigned number_of_tokens = 0;
o_tokens.clear();
pos = i_source.find_first_of(i_seperators, pos);
while (pos != std::string::npos)
{
std::string token = i_source.substr(prev_pos, pos - prev_pos);
if (!i_discard_empty_tokens || token != "")
{
o_tokens.push_back(i_source.substr(prev_pos, pos - prev_pos));
number_of_tokens++;
}
pos++;
prev_pos = pos;
pos = i_source.find_first_of(i_seperators, pos);
}
if (prev_pos < i_source.length())
{
o_tokens.push_back(i_source.substr(prev_pos));
number_of_tokens++;
}
return number_of_tokens;
}
Cowardly disclaimer: I write real-time data processing software where the data comes in through binary files, sockets, or some API call (I/O cards, camera's). I never use this function for something more complicated or time-critical than reading external configuration files on startup.
You can simply use a regular expression library and solve that using regular expressions.
Use expression (\w+) and the variable in \1 (or $1 depending on the library implementation of regular expressions).
Many overly complicated suggestions here. Try this simple std::string solution:
using namespace std;
string someText = ...
string::size_type tokenOff = 0, sepOff = tokenOff;
while (sepOff != string::npos)
{
sepOff = someText.find(' ', sepOff);
string::size_type tokenLen = (sepOff == string::npos) ? sepOff : sepOff++ - tokenOff;
string token = someText.substr(tokenOff, tokenLen);
if (!token.empty())
/* do something with token */;
tokenOff = sepOff;
}
I thought that was what the >> operator on string streams was for:
string word; sin >> word;
Here's an approach that allows you control over whether empty tokens are included (like strsep) or excluded (like strtok).
#include <string.h> // for strchr and strlen
/*
* want_empty_tokens==true : include empty tokens, like strsep()
* want_empty_tokens==false : exclude empty tokens, like strtok()
*/
std::vector<std::string> tokenize(const char* src,
char delim,
bool want_empty_tokens)
{
std::vector<std::string> tokens;
if (src and *src != '\0') // defensive
while( true ) {
const char* d = strchr(src, delim);
size_t len = (d)? d-src : strlen(src);
if (len or want_empty_tokens)
tokens.push_back( std::string(src, len) ); // capture token
if (d) src += len+1; else break;
}
return tokens;
}
Seems odd to me that with all us speed conscious nerds here on SO no one has presented a version that uses a compile time generated look up table for the delimiter (example implementation further down). Using a look up table and iterators should beat std::regex in efficiency, if you don't need to beat regex, just use it, its standard as of C++11 and super flexible.
Some have suggested regex already but for the noobs here is a packaged example that should do exactly what the OP expects:
std::vector<std::string> split(std::string::const_iterator it, std::string::const_iterator end, std::regex e = std::regex{"\\w+"}){
std::smatch m{};
std::vector<std::string> ret{};
while (std::regex_search (it,end,m,e)) {
ret.emplace_back(m.str());
std::advance(it, m.position() + m.length()); //next start position = match position + match length
}
return ret;
}
std::vector<std::string> split(const std::string &s, std::regex e = std::regex{"\\w+"}){ //comfort version calls flexible version
return split(s.cbegin(), s.cend(), std::move(e));
}
int main ()
{
std::string str {"Some people, excluding those present, have been compile time constants - since puberty."};
auto v = split(str);
for(const auto&s:v){
std::cout << s << std::endl;
}
std::cout << "crazy version:" << std::endl;
v = split(str, std::regex{"[^e]+"}); //using e as delim shows flexibility
for(const auto&s:v){
std::cout << s << std::endl;
}
return 0;
}
If we need to be faster and accept the constraint that all chars must be 8 bits we can make a look up table at compile time using metaprogramming:
template<bool...> struct BoolSequence{}; //just here to hold bools
template<char...> struct CharSequence{}; //just here to hold chars
template<typename T, char C> struct Contains; //generic
template<char First, char... Cs, char Match> //not first specialization
struct Contains<CharSequence<First, Cs...>,Match> :
Contains<CharSequence<Cs...>, Match>{}; //strip first and increase index
template<char First, char... Cs> //is first specialization
struct Contains<CharSequence<First, Cs...>,First>: std::true_type {};
template<char Match> //not found specialization
struct Contains<CharSequence<>,Match>: std::false_type{};
template<int I, typename T, typename U>
struct MakeSequence; //generic
template<int I, bool... Bs, typename U>
struct MakeSequence<I,BoolSequence<Bs...>, U>: //not last
MakeSequence<I-1, BoolSequence<Contains<U,I-1>::value,Bs...>, U>{};
template<bool... Bs, typename U>
struct MakeSequence<0,BoolSequence<Bs...>,U>{ //last
using Type = BoolSequence<Bs...>;
};
template<typename T> struct BoolASCIITable;
template<bool... Bs> struct BoolASCIITable<BoolSequence<Bs...>>{
/* could be made constexpr but not yet supported by MSVC */
static bool isDelim(const char c){
static const bool table[256] = {Bs...};
return table[static_cast<int>(c)];
}
};
using Delims = CharSequence<'.',',',' ',':','\n'>; //list your custom delimiters here
using Table = BoolASCIITable<typename MakeSequence<256,BoolSequence<>,Delims>::Type>;
With that in place making a getNextToken function is easy:
template<typename T_It>
std::pair<T_It,T_It> getNextToken(T_It begin,T_It end){
begin = std::find_if(begin,end,std::not1(Table{})); //find first non delim or end
auto second = std::find_if(begin,end,Table{}); //find first delim or end
return std::make_pair(begin,second);
}
Using it is also easy:
int main() {
std::string s{"Some people, excluding those present, have been compile time constants - since puberty."};
auto it = std::begin(s);
auto end = std::end(s);
while(it != std::end(s)){
auto token = getNextToken(it,end);
std::cout << std::string(token.first,token.second) << std::endl;
it = token.second;
}
return 0;
}
Here is a live example: http://ideone.com/GKtkLQ
I know this question is already answered but I want to contribute. Maybe my solution is a bit simple but this is what I came up with:
vector<string> get_words(string const& text, string const& separator)
{
vector<string> result;
string tmp = text;
size_t first_pos = 0;
size_t second_pos = tmp.find(separator);
while (second_pos != string::npos)
{
if (first_pos != second_pos)
{
string word = tmp.substr(first_pos, second_pos - first_pos);
result.push_back(word);
}
tmp = tmp.substr(second_pos + separator.length());
second_pos = tmp.find(separator);
}
result.push_back(tmp);
return result;
}
Please comment if there is a better approach to something in my code or if something is wrong.
UPDATE: added generic separator
you can take advantage of boost::make_find_iterator. Something similar to this:
template<typename CH>
inline vector< basic_string<CH> > tokenize(
const basic_string<CH> &Input,
const basic_string<CH> &Delimiter,
bool remove_empty_token
) {
typedef typename basic_string<CH>::const_iterator string_iterator_t;
typedef boost::find_iterator< string_iterator_t > string_find_iterator_t;
vector< basic_string<CH> > Result;
string_iterator_t it = Input.begin();
string_iterator_t it_end = Input.end();
for(string_find_iterator_t i = boost::make_find_iterator(Input, boost::first_finder(Delimiter, boost::is_equal()));
i != string_find_iterator_t();
++i) {
if(remove_empty_token){
if(it != i->begin())
Result.push_back(basic_string<CH>(it,i->begin()));
}
else
Result.push_back(basic_string<CH>(it,i->begin()));
it = i->end();
}
if(it != it_end)
Result.push_back(basic_string<CH>(it,it_end));
return Result;
}
Here's my Swiss® Army Knife of string-tokenizers for splitting up strings by whitespace, accounting for single and double-quote wrapped strings as well as stripping those characters from the results. I used RegexBuddy 4.x to generate most of the code-snippet, but I added custom handling for stripping quotes and a few other things.
#include <string>
#include <locale>
#include <regex>
std::vector<std::wstring> tokenize_string(std::wstring string_to_tokenize) {
std::vector<std::wstring> tokens;
std::wregex re(LR"(("[^"]*"|'[^']*'|[^"' ]+))", std::regex_constants::collate);
std::wsregex_iterator next( string_to_tokenize.begin(),
string_to_tokenize.end(),
re,
std::regex_constants::match_not_null );
std::wsregex_iterator end;
const wchar_t single_quote = L'\'';
const wchar_t double_quote = L'\"';
while ( next != end ) {
std::wsmatch match = *next;
const std::wstring token = match.str( 0 );
next++;
if (token.length() > 2 && (token.front() == double_quote || token.front() == single_quote))
tokens.emplace_back( std::wstring(token.begin()+1, token.begin()+token.length()-1) );
else
tokens.emplace_back(token);
}
return tokens;
}
I wrote a simplified version (and maybe a little bit efficient) of https://stackoverflow.com/a/50247503/3976739 for my own use. I hope it would help.
void StrTokenizer(string& source, const char* delimiter, vector<string>& Tokens)
{
size_t new_index = 0;
size_t old_index = 0;
while (new_index != std::string::npos)
{
new_index = source.find(delimiter, old_index);
Tokens.emplace_back(source.substr(old_index, new_index-old_index));
if (new_index != std::string::npos)
old_index = ++new_index;
}
}
If the maximum length of the input string to be tokenized is known, one can exploit this and implement a very fast version. I am sketching the basic idea below, which was inspired by both strtok() and the "suffix array"-data structure described Jon Bentley's "Programming Perls" 2nd edition, chapter 15. The C++ class in this case only gives some organization and convenience of use. The implementation shown can be easily extended for removing leading and trailing whitespace characters in the tokens.
Basically one can replace the separator characters with string-terminating '\0'-characters and set pointers to the tokens withing the modified string. In the extreme case when the string consists only of separators, one gets string-length plus 1 resulting empty tokens. It is practical to duplicate the string to be modified.
Header file:
class TextLineSplitter
{
public:
TextLineSplitter( const size_t max_line_len );
~TextLineSplitter();
void SplitLine( const char *line,
const char sep_char = ',',
);
inline size_t NumTokens( void ) const
{
return mNumTokens;
}
const char * GetToken( const size_t token_idx ) const
{
assert( token_idx < mNumTokens );
return mTokens[ token_idx ];
}
private:
const size_t mStorageSize;
char *mBuff;
char **mTokens;
size_t mNumTokens;
inline void ResetContent( void )
{
memset( mBuff, 0, mStorageSize );
// mark all items as empty:
memset( mTokens, 0, mStorageSize * sizeof( char* ) );
// reset counter for found items:
mNumTokens = 0L;
}
};
Implementattion file:
TextLineSplitter::TextLineSplitter( const size_t max_line_len ):
mStorageSize ( max_line_len + 1L )
{
// allocate memory
mBuff = new char [ mStorageSize ];
mTokens = new char* [ mStorageSize ];
ResetContent();
}
TextLineSplitter::~TextLineSplitter()
{
delete [] mBuff;
delete [] mTokens;
}
void TextLineSplitter::SplitLine( const char *line,
const char sep_char /* = ',' */,
)
{
assert( sep_char != '\0' );
ResetContent();
strncpy( mBuff, line, mMaxLineLen );
size_t idx = 0L; // running index for characters
do
{
assert( idx < mStorageSize );
const char chr = line[ idx ]; // retrieve current character
if( mTokens[ mNumTokens ] == NULL )
{
mTokens[ mNumTokens ] = &mBuff[ idx ];
} // if
if( chr == sep_char || chr == '\0' )
{ // item or line finished
// overwrite separator with a 0-terminating character:
mBuff[ idx ] = '\0';
// count-up items:
mNumTokens ++;
} // if
} while( line[ idx++ ] );
}
A scenario of usage would be:
// create an instance capable of splitting strings up to 1000 chars long:
TextLineSplitter spl( 1000 );
spl.SplitLine( "Item1,,Item2,Item3" );
for( size_t i = 0; i < spl.NumTokens(); i++ )
{
printf( "%s\n", spl.GetToken( i ) );
}
output:
Item1
Item2
Item3
If I wanted to iterate over individual words in a string (separated by whitespace), then the obvious solution would be:
std::istringstream s(myString);
std::string word;
while (s >> word)
do things
However that's quite inefficient. The entire string is copied while initializing the string stream, and then each extracted word is copied one at a time into the word variable (which is close to copying the entire string for a second time). Is there a way to improve on this without manually iterating over each character?
In most cases, copying represents a very small percentage of the overall costs, so having a clean, highly readable code becomes more important. In rare cases when the time profiler tells you that copying creates a bottleneck, you can iterate over characters in the string with some help from the standard library.
One approach that you could take is to iterate with std::string::find_first_of and std::string::find_first_not_of member functions, like this:
const std::string s = "quick \t\t brown \t fox jumps over the\nlazy dog";
const std::string ws = " \t\r\n";
std::size_t pos = 0;
while (pos != s.size()) {
std::size_t from = s.find_first_not_of(ws, pos);
if (from == std::string::npos) {
break;
}
std::size_t to = s.find_first_of(ws, from+1);
if (to == std::string::npos) {
to = s.size();
}
// If you want an individual word, copy it with substr.
// The code below simply prints it character-by-character:
std::cout << "'";
for (std::size_t i = from ; i != to ; i++) {
std::cout << s[i];
}
std::cout << "'" << std::endl;
pos = to;
}
Demo.
Unfortunately, the code becomes a lot harder to read, so you should avoid this change, or at least postpone it until it becomes requried.
Using boost string algorithms we can write it as follows.
The loop doesn't involve any copying of the string.
#include <string>
#include <iostream>
#include <boost/algorithm/string.hpp>
int main()
{
std::string s = "stack over flow";
auto it = boost::make_split_iterator( s, boost::token_finder(
boost::is_any_of( " " ), boost::algorithm::token_compress_on ) );
decltype( it ) end;
for( ; it != end; ++it )
{
std::cout << "word: '" << *it << "'\n";
}
return 0;
}
Making it C++11-ish
Since pairs of iterators are so oldschool nowadays, we may use boost.range to define some generic helper functions. These finally allow us to loop over the words using range-for:
#include <string>
#include <iostream>
#include <boost/algorithm/string.hpp>
#include <boost/range/iterator_range_core.hpp>
template< typename Range >
using SplitRange = boost::iterator_range< boost::split_iterator< typename Range::const_iterator > >;
template< typename Range, typename Finder >
SplitRange< Range > make_split_range( const Range& rng, const Finder& finder )
{
auto first = boost::make_split_iterator( rng, finder );
decltype( first ) last;
return { first, last };
}
template< typename Range, typename Predicate >
SplitRange< Range > make_token_range( const Range& rng, const Predicate& pred )
{
return make_split_range( rng, boost::token_finder( pred, boost::algorithm::token_compress_on ) );
}
int main()
{
std::string str = "stack \tover\r\n flow";
for( const auto& substr : make_token_range( str, boost::is_any_of( " \t\r\n" ) ) )
{
std::cout << "word: '" << substr << "'\n";
}
return 0;
}
Demo:
http://coliru.stacked-crooked.com/a/2f4b3d34086cc6ec
If you want to have it as fast as possible, you need to fall back to the good old C function strtok() (or its thread-safe companion strtok_r()):
const char* kWhiteSpace = " \t\v\n\r"; //whatever you call white space
char* token = std::strtok(myString.data(), kWhiteSpace);
while(token) {
//do things with token
token = std::strtok(nullptr, kWhiteSpace));
}
Beware that this will clobber the contents of myString: It works by replacing the first delimiter character after each token with a terminating null byte, and returning a pointer to the start of the tokens in turn. This is a legacy C function after all.
However, that weakness is also its strength: It does not perform any copy, nor does it allocate any dynamic memory (which likely is the most time consuming thing in your example code). As such, you won't find a native C++ method that beats strtok()'s speed.
What about spliting the string? You can check this post for more information.
Inside this post there is a detailed answer about how to split a string in tokens. In this answer maybe you could check the second way using iterators and the copy algorithm.
Java has a convenient split method:
String str = "The quick brown fox";
String[] results = str.split(" ");
Is there an easy way to do this in C++?
The Boost tokenizer class can make this sort of thing quite simple:
#include <iostream>
#include <string>
#include <boost/foreach.hpp>
#include <boost/tokenizer.hpp>
using namespace std;
using namespace boost;
int main(int, char**)
{
string text = "token, test string";
char_separator<char> sep(", ");
tokenizer< char_separator<char> > tokens(text, sep);
BOOST_FOREACH (const string& t, tokens) {
cout << t << "." << endl;
}
}
Updated for C++11:
#include <iostream>
#include <string>
#include <boost/tokenizer.hpp>
using namespace std;
using namespace boost;
int main(int, char**)
{
string text = "token, test string";
char_separator<char> sep(", ");
tokenizer<char_separator<char>> tokens(text, sep);
for (const auto& t : tokens) {
cout << t << "." << endl;
}
}
Here's a real simple one:
#include <vector>
#include <string>
using namespace std;
vector<string> split(const char *str, char c = ' ')
{
vector<string> result;
do
{
const char *begin = str;
while(*str != c && *str)
str++;
result.push_back(string(begin, str));
} while (0 != *str++);
return result;
}
C++ standard library algorithms are pretty universally based around iterators rather than concrete containers. Unfortunately this makes it hard to provide a Java-like split function in the C++ standard library, even though nobody argues that this would be convenient. But what would its return type be? std::vector<std::basic_string<…>>? Maybe, but then we’re forced to perform (potentially redundant and costly) allocations.
Instead, C++ offers a plethora of ways to split strings based on arbitrarily complex delimiters, but none of them is encapsulated as nicely as in other languages. The numerous ways fill whole blog posts.
At its simplest, you could iterate using std::string::find until you hit std::string::npos, and extract the contents using std::string::substr.
A more fluid (and idiomatic, but basic) version for splitting on whitespace would use a std::istringstream:
auto iss = std::istringstream{"The quick brown fox"};
auto str = std::string{};
while (iss >> str) {
process(str);
}
Using std::istream_iterators, the contents of the string stream could also be copied into a vector using its iterator range constructor.
Multiple libraries (such as Boost.Tokenizer) offer specific tokenisers.
More advanced splitting require regular expressions. C++ provides the std::regex_token_iterator for this purpose in particular:
auto const str = "The quick brown fox"s;
auto const re = std::regex{R"(\s+)"};
auto const vec = std::vector<std::string>(
std::sregex_token_iterator{begin(str), end(str), re, -1},
std::sregex_token_iterator{}
);
Another quick way is to use getline. Something like:
stringstream ss("bla bla");
string s;
while (getline(ss, s, ' ')) {
cout << s << endl;
}
If you want, you can make a simple split() method returning a vector<string>, which is
really useful.
Use strtok. In my opinion, there isn't a need to build a class around tokenizing unless strtok doesn't provide you with what you need. It might not, but in 15+ years of writing various parsing code in C and C++, I've always used strtok. Here is an example
char myString[] = "The quick brown fox";
char *p = strtok(myString, " ");
while (p) {
printf ("Token: %s\n", p);
p = strtok(NULL, " ");
}
A few caveats (which might not suit your needs). The string is "destroyed" in the process, meaning that EOS characters are placed inline in the delimter spots. Correct usage might require you to make a non-const version of the string. You can also change the list of delimiters mid parse.
In my own opinion, the above code is far simpler and easier to use than writing a separate class for it. To me, this is one of those functions that the language provides and it does it well and cleanly. It's simply a "C based" solution. It's appropriate, it's easy, and you don't have to write a lot of extra code :-)
You can use streams, iterators, and the copy algorithm to do this fairly directly.
#include <string>
#include <vector>
#include <iostream>
#include <istream>
#include <ostream>
#include <iterator>
#include <sstream>
#include <algorithm>
int main()
{
std::string str = "The quick brown fox";
// construct a stream from the string
std::stringstream strstr(str);
// use stream iterators to copy the stream to the vector as whitespace separated strings
std::istream_iterator<std::string> it(strstr);
std::istream_iterator<std::string> end;
std::vector<std::string> results(it, end);
// send the vector to stdout.
std::ostream_iterator<std::string> oit(std::cout);
std::copy(results.begin(), results.end(), oit);
}
A solution using regex_token_iterators:
#include <iostream>
#include <regex>
#include <string>
using namespace std;
int main()
{
string str("The quick brown fox");
regex reg("\\s+");
sregex_token_iterator iter(str.begin(), str.end(), reg, -1);
sregex_token_iterator end;
vector<string> vec(iter, end);
for (auto a : vec)
{
cout << a << endl;
}
}
No offense folks, but for such a simple problem, you are making things way too complicated. There are a lot of reasons to use Boost. But for something this simple, it's like hitting a fly with a 20# sledge.
void
split( vector<string> & theStringVector, /* Altered/returned value */
const string & theString,
const string & theDelimiter)
{
UASSERT( theDelimiter.size(), >, 0); // My own ASSERT macro.
size_t start = 0, end = 0;
while ( end != string::npos)
{
end = theString.find( theDelimiter, start);
// If at end, use length=maxLength. Else use length=end-start.
theStringVector.push_back( theString.substr( start,
(end == string::npos) ? string::npos : end - start));
// If at end, use start=maxSize. Else use start=end+delimiter.
start = ( ( end > (string::npos - theDelimiter.size()) )
? string::npos : end + theDelimiter.size());
}
}
For example (for Doug's case),
#define SHOW(I,X) cout << "[" << (I) << "]\t " # X " = \"" << (X) << "\"" << endl
int
main()
{
vector<string> v;
split( v, "A:PEP:909:Inventory Item", ":" );
for (unsigned int i = 0; i < v.size(); i++)
SHOW( i, v[i] );
}
And yes, we could have split() return a new vector rather than passing one in. It's trivial to wrap and overload. But depending on what I'm doing, I often find it better to re-use pre-existing objects rather than always creating new ones. (Just as long as I don't forget to empty the vector in between!)
Reference: http://www.cplusplus.com/reference/string/string/.
(I was originally writing a response to Doug's question: C++ Strings Modifying and Extracting based on Separators (closed). But since Martin York closed that question with a pointer over here... I'll just generalize my code.)
Boost has a strong split function: boost::algorithm::split.
Sample program:
#include <vector>
#include <boost/algorithm/string.hpp>
int main() {
auto s = "a,b, c ,,e,f,";
std::vector<std::string> fields;
boost::split(fields, s, boost::is_any_of(","));
for (const auto& field : fields)
std::cout << "\"" << field << "\"\n";
return 0;
}
Output:
"a"
"b"
" c "
""
"e"
"f"
""
This is a simple STL-only solution (~5 lines!) using std::find and std::find_first_not_of that handles repetitions of the delimiter (like spaces or periods for instance), as well leading and trailing delimiters:
#include <string>
#include <vector>
void tokenize(std::string str, std::vector<string> &token_v){
size_t start = str.find_first_not_of(DELIMITER), end=start;
while (start != std::string::npos){
// Find next occurence of delimiter
end = str.find(DELIMITER, start);
// Push back the token found into vector
token_v.push_back(str.substr(start, end-start));
// Skip all occurences of the delimiter to find new start
start = str.find_first_not_of(DELIMITER, end);
}
}
Try it out live!
I know you asked for a C++ solution, but you might consider this helpful:
Qt
#include <QString>
...
QString str = "The quick brown fox";
QStringList results = str.split(" ");
The advantage over Boost in this example is that it's a direct one to one mapping to your post's code.
See more at Qt documentation
Here is a sample tokenizer class that might do what you want
//Header file
class Tokenizer
{
public:
static const std::string DELIMITERS;
Tokenizer(const std::string& str);
Tokenizer(const std::string& str, const std::string& delimiters);
bool NextToken();
bool NextToken(const std::string& delimiters);
const std::string GetToken() const;
void Reset();
protected:
size_t m_offset;
const std::string m_string;
std::string m_token;
std::string m_delimiters;
};
//CPP file
const std::string Tokenizer::DELIMITERS(" \t\n\r");
Tokenizer::Tokenizer(const std::string& s) :
m_string(s),
m_offset(0),
m_delimiters(DELIMITERS) {}
Tokenizer::Tokenizer(const std::string& s, const std::string& delimiters) :
m_string(s),
m_offset(0),
m_delimiters(delimiters) {}
bool Tokenizer::NextToken()
{
return NextToken(m_delimiters);
}
bool Tokenizer::NextToken(const std::string& delimiters)
{
size_t i = m_string.find_first_not_of(delimiters, m_offset);
if (std::string::npos == i)
{
m_offset = m_string.length();
return false;
}
size_t j = m_string.find_first_of(delimiters, i);
if (std::string::npos == j)
{
m_token = m_string.substr(i);
m_offset = m_string.length();
return true;
}
m_token = m_string.substr(i, j - i);
m_offset = j;
return true;
}
Example:
std::vector <std::string> v;
Tokenizer s("split this string", " ");
while (s.NextToken())
{
v.push_back(s.GetToken());
}
pystring is a small library which implements a bunch of Python's string functions, including the split method:
#include <string>
#include <vector>
#include "pystring.h"
std::vector<std::string> chunks;
pystring::split("this string", chunks);
// also can specify a separator
pystring::split("this-string", chunks, "-");
I posted this answer for similar question.
Don't reinvent the wheel. I've used a number of libraries and the fastest and most flexible I have come across is: C++ String Toolkit Library.
Here is an example of how to use it that I've posted else where on the stackoverflow.
#include <iostream>
#include <vector>
#include <string>
#include <strtk.hpp>
const char *whitespace = " \t\r\n\f";
const char *whitespace_and_punctuation = " \t\r\n\f;,=";
int main()
{
{ // normal parsing of a string into a vector of strings
std::string s("Somewhere down the road");
std::vector<std::string> result;
if( strtk::parse( s, whitespace, result ) )
{
for(size_t i = 0; i < result.size(); ++i )
std::cout << result[i] << std::endl;
}
}
{ // parsing a string into a vector of floats with other separators
// besides spaces
std::string s("3.0, 3.14; 4.0");
std::vector<float> values;
if( strtk::parse( s, whitespace_and_punctuation, values ) )
{
for(size_t i = 0; i < values.size(); ++i )
std::cout << values[i] << std::endl;
}
}
{ // parsing a string into specific variables
std::string s("angle = 45; radius = 9.9");
std::string w1, w2;
float v1, v2;
if( strtk::parse( s, whitespace_and_punctuation, w1, v1, w2, v2) )
{
std::cout << "word " << w1 << ", value " << v1 << std::endl;
std::cout << "word " << w2 << ", value " << v2 << std::endl;
}
}
return 0;
}
Adam Pierce's answer provides an hand-spun tokenizer taking in a const char*. It's a bit more problematic to do with iterators because incrementing a string's end iterator is undefined. That said, given string str{ "The quick brown fox" } we can certainly accomplish this:
auto start = find(cbegin(str), cend(str), ' ');
vector<string> tokens{ string(cbegin(str), start) };
while (start != cend(str)) {
const auto finish = find(++start, cend(str), ' ');
tokens.push_back(string(start, finish));
start = finish;
}
Live Example
If you're looking to abstract complexity by using standard functionality, as On Freund suggests strtok is a simple option:
vector<string> tokens;
for (auto i = strtok(data(str), " "); i != nullptr; i = strtok(nullptr, " ")) tokens.push_back(i);
If you don't have access to C++17 you'll need to substitute data(str) as in this example: http://ideone.com/8kAGoa
Though not demonstrated in the example, strtok need not use the same delimiter for each token. Along with this advantage though, there are several drawbacks:
strtok cannot be used on multiple strings at the same time: Either a nullptr must be passed to continue tokenizing the current string or a new char* to tokenize must be passed (there are some non-standard implementations which do support this however, such as: strtok_s)
For the same reason strtok cannot be used on multiple threads simultaneously (this may however be implementation defined, for example: Visual Studio's implementation is thread safe)
Calling strtok modifies the string it is operating on, so it cannot be used on const strings, const char*s, or literal strings, to tokenize any of these with strtok or to operate on a string who's contents need to be preserved, str would have to be copied, then the copy could be operated on
c++20 provides us with split_view to tokenize strings, in a non-destructive manner: https://topanswers.xyz/cplusplus?q=749#a874
The previous methods cannot generate a tokenized vector in-place, meaning without abstracting them into a helper function they cannot initialize const vector<string> tokens. That functionality and the ability to accept any white-space delimiter can be harnessed using an istream_iterator. For example given: const string str{ "The quick \tbrown \nfox" } we can do this:
istringstream is{ str };
const vector<string> tokens{ istream_iterator<string>(is), istream_iterator<string>() };
Live Example
The required construction of an istringstream for this option has far greater cost than the previous 2 options, however this cost is typically hidden in the expense of string allocation.
If none of the above options are flexable enough for your tokenization needs, the most flexible option is using a regex_token_iterator of course with this flexibility comes greater expense, but again this is likely hidden in the string allocation cost. Say for example we want to tokenize based on non-escaped commas, also eating white-space, given the following input: const string str{ "The ,qu\\,ick ,\tbrown, fox" } we can do this:
const regex re{ "\\s*((?:[^\\\\,]|\\\\.)*?)\\s*(?:,|$)" };
const vector<string> tokens{ sregex_token_iterator(cbegin(str), cend(str), re, 1), sregex_token_iterator() };
Live Example
Check this example. It might help you..
#include <iostream>
#include <sstream>
using namespace std;
int main ()
{
string tmps;
istringstream is ("the dellimiter is the space");
while (is.good ()) {
is >> tmps;
cout << tmps << "\n";
}
return 0;
}
If you're using C++ ranges - the full ranges-v3 library, not the limited functionality accepted into C++20 - you could do it this way:
auto results = str | ranges::views::tokenize(" ",1);
... and this is lazily-evaluated. You can alternatively set a vector to this range:
auto results = str | ranges::views::tokenize(" ",1) | ranges::to<std::vector>();
this will take O(m) space and O(n) time if str has n characters making up m words.
See also the library's own tokenization example, here.
MFC/ATL has a very nice tokenizer. From MSDN:
CAtlString str( "%First Second#Third" );
CAtlString resToken;
int curPos= 0;
resToken= str.Tokenize("% #",curPos);
while (resToken != "")
{
printf("Resulting token: %s\n", resToken);
resToken= str.Tokenize("% #",curPos);
};
Output
Resulting Token: First
Resulting Token: Second
Resulting Token: Third
If you're willing to use C, you can use the strtok function. You should pay attention to multi-threading issues when using it.
For simple stuff I just use the following:
unsigned TokenizeString(const std::string& i_source,
const std::string& i_seperators,
bool i_discard_empty_tokens,
std::vector<std::string>& o_tokens)
{
unsigned prev_pos = 0;
unsigned pos = 0;
unsigned number_of_tokens = 0;
o_tokens.clear();
pos = i_source.find_first_of(i_seperators, pos);
while (pos != std::string::npos)
{
std::string token = i_source.substr(prev_pos, pos - prev_pos);
if (!i_discard_empty_tokens || token != "")
{
o_tokens.push_back(i_source.substr(prev_pos, pos - prev_pos));
number_of_tokens++;
}
pos++;
prev_pos = pos;
pos = i_source.find_first_of(i_seperators, pos);
}
if (prev_pos < i_source.length())
{
o_tokens.push_back(i_source.substr(prev_pos));
number_of_tokens++;
}
return number_of_tokens;
}
Cowardly disclaimer: I write real-time data processing software where the data comes in through binary files, sockets, or some API call (I/O cards, camera's). I never use this function for something more complicated or time-critical than reading external configuration files on startup.
You can simply use a regular expression library and solve that using regular expressions.
Use expression (\w+) and the variable in \1 (or $1 depending on the library implementation of regular expressions).
Many overly complicated suggestions here. Try this simple std::string solution:
using namespace std;
string someText = ...
string::size_type tokenOff = 0, sepOff = tokenOff;
while (sepOff != string::npos)
{
sepOff = someText.find(' ', sepOff);
string::size_type tokenLen = (sepOff == string::npos) ? sepOff : sepOff++ - tokenOff;
string token = someText.substr(tokenOff, tokenLen);
if (!token.empty())
/* do something with token */;
tokenOff = sepOff;
}
I thought that was what the >> operator on string streams was for:
string word; sin >> word;
Here's an approach that allows you control over whether empty tokens are included (like strsep) or excluded (like strtok).
#include <string.h> // for strchr and strlen
/*
* want_empty_tokens==true : include empty tokens, like strsep()
* want_empty_tokens==false : exclude empty tokens, like strtok()
*/
std::vector<std::string> tokenize(const char* src,
char delim,
bool want_empty_tokens)
{
std::vector<std::string> tokens;
if (src and *src != '\0') // defensive
while( true ) {
const char* d = strchr(src, delim);
size_t len = (d)? d-src : strlen(src);
if (len or want_empty_tokens)
tokens.push_back( std::string(src, len) ); // capture token
if (d) src += len+1; else break;
}
return tokens;
}
Seems odd to me that with all us speed conscious nerds here on SO no one has presented a version that uses a compile time generated look up table for the delimiter (example implementation further down). Using a look up table and iterators should beat std::regex in efficiency, if you don't need to beat regex, just use it, its standard as of C++11 and super flexible.
Some have suggested regex already but for the noobs here is a packaged example that should do exactly what the OP expects:
std::vector<std::string> split(std::string::const_iterator it, std::string::const_iterator end, std::regex e = std::regex{"\\w+"}){
std::smatch m{};
std::vector<std::string> ret{};
while (std::regex_search (it,end,m,e)) {
ret.emplace_back(m.str());
std::advance(it, m.position() + m.length()); //next start position = match position + match length
}
return ret;
}
std::vector<std::string> split(const std::string &s, std::regex e = std::regex{"\\w+"}){ //comfort version calls flexible version
return split(s.cbegin(), s.cend(), std::move(e));
}
int main ()
{
std::string str {"Some people, excluding those present, have been compile time constants - since puberty."};
auto v = split(str);
for(const auto&s:v){
std::cout << s << std::endl;
}
std::cout << "crazy version:" << std::endl;
v = split(str, std::regex{"[^e]+"}); //using e as delim shows flexibility
for(const auto&s:v){
std::cout << s << std::endl;
}
return 0;
}
If we need to be faster and accept the constraint that all chars must be 8 bits we can make a look up table at compile time using metaprogramming:
template<bool...> struct BoolSequence{}; //just here to hold bools
template<char...> struct CharSequence{}; //just here to hold chars
template<typename T, char C> struct Contains; //generic
template<char First, char... Cs, char Match> //not first specialization
struct Contains<CharSequence<First, Cs...>,Match> :
Contains<CharSequence<Cs...>, Match>{}; //strip first and increase index
template<char First, char... Cs> //is first specialization
struct Contains<CharSequence<First, Cs...>,First>: std::true_type {};
template<char Match> //not found specialization
struct Contains<CharSequence<>,Match>: std::false_type{};
template<int I, typename T, typename U>
struct MakeSequence; //generic
template<int I, bool... Bs, typename U>
struct MakeSequence<I,BoolSequence<Bs...>, U>: //not last
MakeSequence<I-1, BoolSequence<Contains<U,I-1>::value,Bs...>, U>{};
template<bool... Bs, typename U>
struct MakeSequence<0,BoolSequence<Bs...>,U>{ //last
using Type = BoolSequence<Bs...>;
};
template<typename T> struct BoolASCIITable;
template<bool... Bs> struct BoolASCIITable<BoolSequence<Bs...>>{
/* could be made constexpr but not yet supported by MSVC */
static bool isDelim(const char c){
static const bool table[256] = {Bs...};
return table[static_cast<int>(c)];
}
};
using Delims = CharSequence<'.',',',' ',':','\n'>; //list your custom delimiters here
using Table = BoolASCIITable<typename MakeSequence<256,BoolSequence<>,Delims>::Type>;
With that in place making a getNextToken function is easy:
template<typename T_It>
std::pair<T_It,T_It> getNextToken(T_It begin,T_It end){
begin = std::find_if(begin,end,std::not1(Table{})); //find first non delim or end
auto second = std::find_if(begin,end,Table{}); //find first delim or end
return std::make_pair(begin,second);
}
Using it is also easy:
int main() {
std::string s{"Some people, excluding those present, have been compile time constants - since puberty."};
auto it = std::begin(s);
auto end = std::end(s);
while(it != std::end(s)){
auto token = getNextToken(it,end);
std::cout << std::string(token.first,token.second) << std::endl;
it = token.second;
}
return 0;
}
Here is a live example: http://ideone.com/GKtkLQ
I know this question is already answered but I want to contribute. Maybe my solution is a bit simple but this is what I came up with:
vector<string> get_words(string const& text, string const& separator)
{
vector<string> result;
string tmp = text;
size_t first_pos = 0;
size_t second_pos = tmp.find(separator);
while (second_pos != string::npos)
{
if (first_pos != second_pos)
{
string word = tmp.substr(first_pos, second_pos - first_pos);
result.push_back(word);
}
tmp = tmp.substr(second_pos + separator.length());
second_pos = tmp.find(separator);
}
result.push_back(tmp);
return result;
}
Please comment if there is a better approach to something in my code or if something is wrong.
UPDATE: added generic separator
you can take advantage of boost::make_find_iterator. Something similar to this:
template<typename CH>
inline vector< basic_string<CH> > tokenize(
const basic_string<CH> &Input,
const basic_string<CH> &Delimiter,
bool remove_empty_token
) {
typedef typename basic_string<CH>::const_iterator string_iterator_t;
typedef boost::find_iterator< string_iterator_t > string_find_iterator_t;
vector< basic_string<CH> > Result;
string_iterator_t it = Input.begin();
string_iterator_t it_end = Input.end();
for(string_find_iterator_t i = boost::make_find_iterator(Input, boost::first_finder(Delimiter, boost::is_equal()));
i != string_find_iterator_t();
++i) {
if(remove_empty_token){
if(it != i->begin())
Result.push_back(basic_string<CH>(it,i->begin()));
}
else
Result.push_back(basic_string<CH>(it,i->begin()));
it = i->end();
}
if(it != it_end)
Result.push_back(basic_string<CH>(it,it_end));
return Result;
}
Here's my Swiss® Army Knife of string-tokenizers for splitting up strings by whitespace, accounting for single and double-quote wrapped strings as well as stripping those characters from the results. I used RegexBuddy 4.x to generate most of the code-snippet, but I added custom handling for stripping quotes and a few other things.
#include <string>
#include <locale>
#include <regex>
std::vector<std::wstring> tokenize_string(std::wstring string_to_tokenize) {
std::vector<std::wstring> tokens;
std::wregex re(LR"(("[^"]*"|'[^']*'|[^"' ]+))", std::regex_constants::collate);
std::wsregex_iterator next( string_to_tokenize.begin(),
string_to_tokenize.end(),
re,
std::regex_constants::match_not_null );
std::wsregex_iterator end;
const wchar_t single_quote = L'\'';
const wchar_t double_quote = L'\"';
while ( next != end ) {
std::wsmatch match = *next;
const std::wstring token = match.str( 0 );
next++;
if (token.length() > 2 && (token.front() == double_quote || token.front() == single_quote))
tokens.emplace_back( std::wstring(token.begin()+1, token.begin()+token.length()-1) );
else
tokens.emplace_back(token);
}
return tokens;
}
I wrote a simplified version (and maybe a little bit efficient) of https://stackoverflow.com/a/50247503/3976739 for my own use. I hope it would help.
void StrTokenizer(string& source, const char* delimiter, vector<string>& Tokens)
{
size_t new_index = 0;
size_t old_index = 0;
while (new_index != std::string::npos)
{
new_index = source.find(delimiter, old_index);
Tokens.emplace_back(source.substr(old_index, new_index-old_index));
if (new_index != std::string::npos)
old_index = ++new_index;
}
}
If the maximum length of the input string to be tokenized is known, one can exploit this and implement a very fast version. I am sketching the basic idea below, which was inspired by both strtok() and the "suffix array"-data structure described Jon Bentley's "Programming Perls" 2nd edition, chapter 15. The C++ class in this case only gives some organization and convenience of use. The implementation shown can be easily extended for removing leading and trailing whitespace characters in the tokens.
Basically one can replace the separator characters with string-terminating '\0'-characters and set pointers to the tokens withing the modified string. In the extreme case when the string consists only of separators, one gets string-length plus 1 resulting empty tokens. It is practical to duplicate the string to be modified.
Header file:
class TextLineSplitter
{
public:
TextLineSplitter( const size_t max_line_len );
~TextLineSplitter();
void SplitLine( const char *line,
const char sep_char = ',',
);
inline size_t NumTokens( void ) const
{
return mNumTokens;
}
const char * GetToken( const size_t token_idx ) const
{
assert( token_idx < mNumTokens );
return mTokens[ token_idx ];
}
private:
const size_t mStorageSize;
char *mBuff;
char **mTokens;
size_t mNumTokens;
inline void ResetContent( void )
{
memset( mBuff, 0, mStorageSize );
// mark all items as empty:
memset( mTokens, 0, mStorageSize * sizeof( char* ) );
// reset counter for found items:
mNumTokens = 0L;
}
};
Implementattion file:
TextLineSplitter::TextLineSplitter( const size_t max_line_len ):
mStorageSize ( max_line_len + 1L )
{
// allocate memory
mBuff = new char [ mStorageSize ];
mTokens = new char* [ mStorageSize ];
ResetContent();
}
TextLineSplitter::~TextLineSplitter()
{
delete [] mBuff;
delete [] mTokens;
}
void TextLineSplitter::SplitLine( const char *line,
const char sep_char /* = ',' */,
)
{
assert( sep_char != '\0' );
ResetContent();
strncpy( mBuff, line, mMaxLineLen );
size_t idx = 0L; // running index for characters
do
{
assert( idx < mStorageSize );
const char chr = line[ idx ]; // retrieve current character
if( mTokens[ mNumTokens ] == NULL )
{
mTokens[ mNumTokens ] = &mBuff[ idx ];
} // if
if( chr == sep_char || chr == '\0' )
{ // item or line finished
// overwrite separator with a 0-terminating character:
mBuff[ idx ] = '\0';
// count-up items:
mNumTokens ++;
} // if
} while( line[ idx++ ] );
}
A scenario of usage would be:
// create an instance capable of splitting strings up to 1000 chars long:
TextLineSplitter spl( 1000 );
spl.SplitLine( "Item1,,Item2,Item3" );
for( size_t i = 0; i < spl.NumTokens(); i++ )
{
printf( "%s\n", spl.GetToken( i ) );
}
output:
Item1
Item2
Item3
What is the effective way to replace all occurrences of a character with another character in std::string?
std::string doesn't contain such function but you could use stand-alone replace function from algorithm header.
#include <algorithm>
#include <string>
void some_func() {
std::string s = "example string";
std::replace( s.begin(), s.end(), 'x', 'y'); // replace all 'x' to 'y'
}
The question is centered on character replacement, but, as I found this page very useful (especially Konrad's remark), I'd like to share this more generalized implementation, which allows to deal with substrings as well:
std::string ReplaceAll(std::string str, const std::string& from, const std::string& to) {
size_t start_pos = 0;
while((start_pos = str.find(from, start_pos)) != std::string::npos) {
str.replace(start_pos, from.length(), to);
start_pos += to.length(); // Handles case where 'to' is a substring of 'from'
}
return str;
}
Usage:
std::cout << ReplaceAll(string("Number Of Beans"), std::string(" "), std::string("_")) << std::endl;
std::cout << ReplaceAll(string("ghghjghugtghty"), std::string("gh"), std::string("X")) << std::endl;
std::cout << ReplaceAll(string("ghghjghugtghty"), std::string("gh"), std::string("h")) << std::endl;
Outputs:
Number_Of_Beans
XXjXugtXty
hhjhugthty
EDIT:
The above can be implemented in a more suitable way, in case performance is of your concern, by returning nothing (void) and performing the changes "in-place"; that is, by directly modifying the string argument str, passed by reference instead of by value. This would avoid an extra costly copy of the original string by overwriting it.
Code :
static inline void ReplaceAll2(std::string &str, const std::string& from, const std::string& to)
{
// Same inner code...
// No return statement
}
Hope this will be helpful for some others...
I thought I'd toss in the boost solution as well:
#include <boost/algorithm/string/replace.hpp>
// in place
std::string in_place = "blah#blah";
boost::replace_all(in_place, "#", "#");
// copy
const std::string input = "blah#blah";
std::string output = boost::replace_all_copy(input, "#", "#");
Imagine a large binary blob where all 0x00 bytes shall be replaced by "\1\x30" and all 0x01 bytes by "\1\x31" because the transport protocol allows no \0-bytes.
In cases where:
the replacing and the to-replaced string have different lengths,
there are many occurences of the to-replaced string within the source string and
the source string is large,
the provided solutions cannot be applied (because they replace only single characters) or have a performance problem, because they would call string::replace several times which generates copies of the size of the blob over and over.
(I do not know the boost solution, maybe it is OK from that perspective)
This one walks along all occurrences in the source string and builds the new string piece by piece once:
void replaceAll(std::string& source, const std::string& from, const std::string& to)
{
std::string newString;
newString.reserve(source.length()); // avoids a few memory allocations
std::string::size_type lastPos = 0;
std::string::size_type findPos;
while(std::string::npos != (findPos = source.find(from, lastPos)))
{
newString.append(source, lastPos, findPos - lastPos);
newString += to;
lastPos = findPos + from.length();
}
// Care for the rest after last occurrence
newString += source.substr(lastPos);
source.swap(newString);
}
A simple find and replace for a single character would go something like:
s.replace(s.find("x"), 1, "y")
To do this for the whole string, the easy thing to do would be to loop until your s.find starts returning npos. I suppose you could also catch range_error to exit the loop, but that's kinda ugly.
For completeness, here's how to do it with std::regex.
#include <regex>
#include <string>
int main()
{
const std::string s = "example string";
const std::string r = std::regex_replace(s, std::regex("x"), "y");
}
If you're looking to replace more than a single character, and are dealing only with std::string, then this snippet would work, replacing sNeedle in sHaystack with sReplace, and sNeedle and sReplace do not need to be the same size. This routine uses the while loop to replace all occurrences, rather than just the first one found from left to right.
while(sHaystack.find(sNeedle) != std::string::npos) {
sHaystack.replace(sHaystack.find(sNeedle),sNeedle.size(),sReplace);
}
As Kirill suggested, either use the replace method or iterate along the string replacing each char independently.
Alternatively you can use the find method or find_first_of depending on what you need to do. None of these solutions will do the job in one go, but with a few extra lines of code you ought to make them work for you. :-)
What about Abseil StrReplaceAll? From the header file:
// This file defines `absl::StrReplaceAll()`, a general-purpose string
// replacement function designed for large, arbitrary text substitutions,
// especially on strings which you are receiving from some other system for
// further processing (e.g. processing regular expressions, escaping HTML
// entities, etc.). `StrReplaceAll` is designed to be efficient even when only
// one substitution is being performed, or when substitution is rare.
//
// If the string being modified is known at compile-time, and the substitutions
// vary, `absl::Substitute()` may be a better choice.
//
// Example:
//
// std::string html_escaped = absl::StrReplaceAll(user_input, {
// {"&", "&"},
// {"<", "<"},
// {">", ">"},
// {"\"", """},
// {"'", "'"}});
#include <iostream>
#include <string>
using namespace std;
// Replace function..
string replace(string word, string target, string replacement){
int len, loop=0;
string nword="", let;
len=word.length();
len--;
while(loop<=len){
let=word.substr(loop, 1);
if(let==target){
nword=nword+replacement;
}else{
nword=nword+let;
}
loop++;
}
return nword;
}
//Main..
int main() {
string word;
cout<<"Enter Word: ";
cin>>word;
cout<<replace(word, "x", "y")<<endl;
return 0;
}
Old School :-)
std::string str = "H:/recursos/audio/youtube/libre/falta/";
for (int i = 0; i < str.size(); i++) {
if (str[i] == '/') {
str[i] = '\\';
}
}
std::cout << str;
Result:
H:\recursos\audio\youtube\libre\falta\
For simple situations this works pretty well without using any other library then std::string (which is already in use).
Replace all occurences of character a with character b in some_string:
for (size_t i = 0; i < some_string.size(); ++i) {
if (some_string[i] == 'a') {
some_string.replace(i, 1, "b");
}
}
If the string is large or multiple calls to replace is an issue, you can apply the technique mentioned in this answer: https://stackoverflow.com/a/29752943/3622300
here's a solution i rolled, in a maximal DRI spirit.
it will search sNeedle in sHaystack and replace it by sReplace,
nTimes if non 0, else all the sNeedle occurences.
it will not search again in the replaced text.
std::string str_replace(
std::string sHaystack, std::string sNeedle, std::string sReplace,
size_t nTimes=0)
{
size_t found = 0, pos = 0, c = 0;
size_t len = sNeedle.size();
size_t replen = sReplace.size();
std::string input(sHaystack);
do {
found = input.find(sNeedle, pos);
if (found == std::string::npos) {
break;
}
input.replace(found, len, sReplace);
pos = found + replen;
++c;
} while(!nTimes || c < nTimes);
return input;
}
I think I'd use std::replace_if()
A simple character-replacer (requested by OP) can be written by using standard library functions.
For an in-place version:
#include <string>
#include <algorithm>
void replace_char(std::string& in,
std::string::value_type srch,
std::string::value_type repl)
{
std::replace_if(std::begin(in), std::end(in),
[&srch](std::string::value_type v) { return v==srch; },
repl);
return;
}
and an overload that returns a copy if the input is a const string:
std::string replace_char(std::string const& in,
std::string::value_type srch,
std::string::value_type repl)
{
std::string result{ in };
replace_char(result, srch, repl);
return result;
}
This works! I used something similar to this for a bookstore app, where the inventory was stored in a CSV (like a .dat file). But in the case of a single char, meaning the replacer is only a single char, e.g.'|', it must be in double quotes "|" in order not to throw an invalid conversion const char.
#include <iostream>
#include <string>
using namespace std;
int main()
{
int count = 0; // for the number of occurences.
// final hold variable of corrected word up to the npos=j
string holdWord = "";
// a temp var in order to replace 0 to new npos
string holdTemp = "";
// a csv for a an entry in a book store
string holdLetter = "Big Java 7th Ed,Horstman,978-1118431115,99.85";
// j = npos
for (int j = 0; j < holdLetter.length(); j++) {
if (holdLetter[j] == ',') {
if ( count == 0 )
{
holdWord = holdLetter.replace(j, 1, " | ");
}
else {
string holdTemp1 = holdLetter.replace(j, 1, " | ");
// since replacement is three positions in length,
// must replace new replacement's 0 to npos-3, with
// the 0 to npos - 3 of the old replacement
holdTemp = holdTemp1.replace(0, j-3, holdWord, 0, j-3);
holdWord = "";
holdWord = holdTemp;
}
holdTemp = "";
count++;
}
}
cout << holdWord << endl;
return 0;
}
// result:
Big Java 7th Ed | Horstman | 978-1118431115 | 99.85
Uncustomarily I am using CentOS currently, so my compiler version is below . The C++ version (g++), C++98 default:
g++ (GCC) 4.8.5 20150623 (Red Hat 4.8.5-4)
Copyright (C) 2015 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
This is not the only method missing from the standard library, it was intended be low level.
This use case and many other are covered by general libraries such as:
POCO
Abseil
Boost
QtCore
QtCore & QString has my preference: it supports UTF8 and uses less templates, which means understandable errors and faster compilation. It uses the "q" prefix which makes namespaces unnecessary and simplifies headers.
Boost often generates hideous error messages and slow compile time.
POCO seems to be a reasonable compromise.
How about replace any character string with any character string using only good-old C string functions?
char original[256]="First Line\nNext Line\n", dest[256]="";
char* replace_this = "\n"; // this is now a single character but could be any string
char* with_this = "\r\n"; // this is 2 characters but could be of any length
/* get the first token */
char* token = strtok(original, replace_this);
/* walk through other tokens */
while (token != NULL) {
strcat(dest, token);
strcat(dest, with_this);
token = strtok(NULL, replace_this);
}
dest should now have what we are looking for.
Java has a convenient split method:
String str = "The quick brown fox";
String[] results = str.split(" ");
Is there an easy way to do this in C++?
The Boost tokenizer class can make this sort of thing quite simple:
#include <iostream>
#include <string>
#include <boost/foreach.hpp>
#include <boost/tokenizer.hpp>
using namespace std;
using namespace boost;
int main(int, char**)
{
string text = "token, test string";
char_separator<char> sep(", ");
tokenizer< char_separator<char> > tokens(text, sep);
BOOST_FOREACH (const string& t, tokens) {
cout << t << "." << endl;
}
}
Updated for C++11:
#include <iostream>
#include <string>
#include <boost/tokenizer.hpp>
using namespace std;
using namespace boost;
int main(int, char**)
{
string text = "token, test string";
char_separator<char> sep(", ");
tokenizer<char_separator<char>> tokens(text, sep);
for (const auto& t : tokens) {
cout << t << "." << endl;
}
}
Here's a real simple one:
#include <vector>
#include <string>
using namespace std;
vector<string> split(const char *str, char c = ' ')
{
vector<string> result;
do
{
const char *begin = str;
while(*str != c && *str)
str++;
result.push_back(string(begin, str));
} while (0 != *str++);
return result;
}
C++ standard library algorithms are pretty universally based around iterators rather than concrete containers. Unfortunately this makes it hard to provide a Java-like split function in the C++ standard library, even though nobody argues that this would be convenient. But what would its return type be? std::vector<std::basic_string<…>>? Maybe, but then we’re forced to perform (potentially redundant and costly) allocations.
Instead, C++ offers a plethora of ways to split strings based on arbitrarily complex delimiters, but none of them is encapsulated as nicely as in other languages. The numerous ways fill whole blog posts.
At its simplest, you could iterate using std::string::find until you hit std::string::npos, and extract the contents using std::string::substr.
A more fluid (and idiomatic, but basic) version for splitting on whitespace would use a std::istringstream:
auto iss = std::istringstream{"The quick brown fox"};
auto str = std::string{};
while (iss >> str) {
process(str);
}
Using std::istream_iterators, the contents of the string stream could also be copied into a vector using its iterator range constructor.
Multiple libraries (such as Boost.Tokenizer) offer specific tokenisers.
More advanced splitting require regular expressions. C++ provides the std::regex_token_iterator for this purpose in particular:
auto const str = "The quick brown fox"s;
auto const re = std::regex{R"(\s+)"};
auto const vec = std::vector<std::string>(
std::sregex_token_iterator{begin(str), end(str), re, -1},
std::sregex_token_iterator{}
);
Another quick way is to use getline. Something like:
stringstream ss("bla bla");
string s;
while (getline(ss, s, ' ')) {
cout << s << endl;
}
If you want, you can make a simple split() method returning a vector<string>, which is
really useful.
Use strtok. In my opinion, there isn't a need to build a class around tokenizing unless strtok doesn't provide you with what you need. It might not, but in 15+ years of writing various parsing code in C and C++, I've always used strtok. Here is an example
char myString[] = "The quick brown fox";
char *p = strtok(myString, " ");
while (p) {
printf ("Token: %s\n", p);
p = strtok(NULL, " ");
}
A few caveats (which might not suit your needs). The string is "destroyed" in the process, meaning that EOS characters are placed inline in the delimter spots. Correct usage might require you to make a non-const version of the string. You can also change the list of delimiters mid parse.
In my own opinion, the above code is far simpler and easier to use than writing a separate class for it. To me, this is one of those functions that the language provides and it does it well and cleanly. It's simply a "C based" solution. It's appropriate, it's easy, and you don't have to write a lot of extra code :-)
You can use streams, iterators, and the copy algorithm to do this fairly directly.
#include <string>
#include <vector>
#include <iostream>
#include <istream>
#include <ostream>
#include <iterator>
#include <sstream>
#include <algorithm>
int main()
{
std::string str = "The quick brown fox";
// construct a stream from the string
std::stringstream strstr(str);
// use stream iterators to copy the stream to the vector as whitespace separated strings
std::istream_iterator<std::string> it(strstr);
std::istream_iterator<std::string> end;
std::vector<std::string> results(it, end);
// send the vector to stdout.
std::ostream_iterator<std::string> oit(std::cout);
std::copy(results.begin(), results.end(), oit);
}
A solution using regex_token_iterators:
#include <iostream>
#include <regex>
#include <string>
using namespace std;
int main()
{
string str("The quick brown fox");
regex reg("\\s+");
sregex_token_iterator iter(str.begin(), str.end(), reg, -1);
sregex_token_iterator end;
vector<string> vec(iter, end);
for (auto a : vec)
{
cout << a << endl;
}
}
No offense folks, but for such a simple problem, you are making things way too complicated. There are a lot of reasons to use Boost. But for something this simple, it's like hitting a fly with a 20# sledge.
void
split( vector<string> & theStringVector, /* Altered/returned value */
const string & theString,
const string & theDelimiter)
{
UASSERT( theDelimiter.size(), >, 0); // My own ASSERT macro.
size_t start = 0, end = 0;
while ( end != string::npos)
{
end = theString.find( theDelimiter, start);
// If at end, use length=maxLength. Else use length=end-start.
theStringVector.push_back( theString.substr( start,
(end == string::npos) ? string::npos : end - start));
// If at end, use start=maxSize. Else use start=end+delimiter.
start = ( ( end > (string::npos - theDelimiter.size()) )
? string::npos : end + theDelimiter.size());
}
}
For example (for Doug's case),
#define SHOW(I,X) cout << "[" << (I) << "]\t " # X " = \"" << (X) << "\"" << endl
int
main()
{
vector<string> v;
split( v, "A:PEP:909:Inventory Item", ":" );
for (unsigned int i = 0; i < v.size(); i++)
SHOW( i, v[i] );
}
And yes, we could have split() return a new vector rather than passing one in. It's trivial to wrap and overload. But depending on what I'm doing, I often find it better to re-use pre-existing objects rather than always creating new ones. (Just as long as I don't forget to empty the vector in between!)
Reference: http://www.cplusplus.com/reference/string/string/.
(I was originally writing a response to Doug's question: C++ Strings Modifying and Extracting based on Separators (closed). But since Martin York closed that question with a pointer over here... I'll just generalize my code.)
Boost has a strong split function: boost::algorithm::split.
Sample program:
#include <vector>
#include <boost/algorithm/string.hpp>
int main() {
auto s = "a,b, c ,,e,f,";
std::vector<std::string> fields;
boost::split(fields, s, boost::is_any_of(","));
for (const auto& field : fields)
std::cout << "\"" << field << "\"\n";
return 0;
}
Output:
"a"
"b"
" c "
""
"e"
"f"
""
This is a simple STL-only solution (~5 lines!) using std::find and std::find_first_not_of that handles repetitions of the delimiter (like spaces or periods for instance), as well leading and trailing delimiters:
#include <string>
#include <vector>
void tokenize(std::string str, std::vector<string> &token_v){
size_t start = str.find_first_not_of(DELIMITER), end=start;
while (start != std::string::npos){
// Find next occurence of delimiter
end = str.find(DELIMITER, start);
// Push back the token found into vector
token_v.push_back(str.substr(start, end-start));
// Skip all occurences of the delimiter to find new start
start = str.find_first_not_of(DELIMITER, end);
}
}
Try it out live!
I know you asked for a C++ solution, but you might consider this helpful:
Qt
#include <QString>
...
QString str = "The quick brown fox";
QStringList results = str.split(" ");
The advantage over Boost in this example is that it's a direct one to one mapping to your post's code.
See more at Qt documentation
Here is a sample tokenizer class that might do what you want
//Header file
class Tokenizer
{
public:
static const std::string DELIMITERS;
Tokenizer(const std::string& str);
Tokenizer(const std::string& str, const std::string& delimiters);
bool NextToken();
bool NextToken(const std::string& delimiters);
const std::string GetToken() const;
void Reset();
protected:
size_t m_offset;
const std::string m_string;
std::string m_token;
std::string m_delimiters;
};
//CPP file
const std::string Tokenizer::DELIMITERS(" \t\n\r");
Tokenizer::Tokenizer(const std::string& s) :
m_string(s),
m_offset(0),
m_delimiters(DELIMITERS) {}
Tokenizer::Tokenizer(const std::string& s, const std::string& delimiters) :
m_string(s),
m_offset(0),
m_delimiters(delimiters) {}
bool Tokenizer::NextToken()
{
return NextToken(m_delimiters);
}
bool Tokenizer::NextToken(const std::string& delimiters)
{
size_t i = m_string.find_first_not_of(delimiters, m_offset);
if (std::string::npos == i)
{
m_offset = m_string.length();
return false;
}
size_t j = m_string.find_first_of(delimiters, i);
if (std::string::npos == j)
{
m_token = m_string.substr(i);
m_offset = m_string.length();
return true;
}
m_token = m_string.substr(i, j - i);
m_offset = j;
return true;
}
Example:
std::vector <std::string> v;
Tokenizer s("split this string", " ");
while (s.NextToken())
{
v.push_back(s.GetToken());
}
pystring is a small library which implements a bunch of Python's string functions, including the split method:
#include <string>
#include <vector>
#include "pystring.h"
std::vector<std::string> chunks;
pystring::split("this string", chunks);
// also can specify a separator
pystring::split("this-string", chunks, "-");
I posted this answer for similar question.
Don't reinvent the wheel. I've used a number of libraries and the fastest and most flexible I have come across is: C++ String Toolkit Library.
Here is an example of how to use it that I've posted else where on the stackoverflow.
#include <iostream>
#include <vector>
#include <string>
#include <strtk.hpp>
const char *whitespace = " \t\r\n\f";
const char *whitespace_and_punctuation = " \t\r\n\f;,=";
int main()
{
{ // normal parsing of a string into a vector of strings
std::string s("Somewhere down the road");
std::vector<std::string> result;
if( strtk::parse( s, whitespace, result ) )
{
for(size_t i = 0; i < result.size(); ++i )
std::cout << result[i] << std::endl;
}
}
{ // parsing a string into a vector of floats with other separators
// besides spaces
std::string s("3.0, 3.14; 4.0");
std::vector<float> values;
if( strtk::parse( s, whitespace_and_punctuation, values ) )
{
for(size_t i = 0; i < values.size(); ++i )
std::cout << values[i] << std::endl;
}
}
{ // parsing a string into specific variables
std::string s("angle = 45; radius = 9.9");
std::string w1, w2;
float v1, v2;
if( strtk::parse( s, whitespace_and_punctuation, w1, v1, w2, v2) )
{
std::cout << "word " << w1 << ", value " << v1 << std::endl;
std::cout << "word " << w2 << ", value " << v2 << std::endl;
}
}
return 0;
}
Adam Pierce's answer provides an hand-spun tokenizer taking in a const char*. It's a bit more problematic to do with iterators because incrementing a string's end iterator is undefined. That said, given string str{ "The quick brown fox" } we can certainly accomplish this:
auto start = find(cbegin(str), cend(str), ' ');
vector<string> tokens{ string(cbegin(str), start) };
while (start != cend(str)) {
const auto finish = find(++start, cend(str), ' ');
tokens.push_back(string(start, finish));
start = finish;
}
Live Example
If you're looking to abstract complexity by using standard functionality, as On Freund suggests strtok is a simple option:
vector<string> tokens;
for (auto i = strtok(data(str), " "); i != nullptr; i = strtok(nullptr, " ")) tokens.push_back(i);
If you don't have access to C++17 you'll need to substitute data(str) as in this example: http://ideone.com/8kAGoa
Though not demonstrated in the example, strtok need not use the same delimiter for each token. Along with this advantage though, there are several drawbacks:
strtok cannot be used on multiple strings at the same time: Either a nullptr must be passed to continue tokenizing the current string or a new char* to tokenize must be passed (there are some non-standard implementations which do support this however, such as: strtok_s)
For the same reason strtok cannot be used on multiple threads simultaneously (this may however be implementation defined, for example: Visual Studio's implementation is thread safe)
Calling strtok modifies the string it is operating on, so it cannot be used on const strings, const char*s, or literal strings, to tokenize any of these with strtok or to operate on a string who's contents need to be preserved, str would have to be copied, then the copy could be operated on
c++20 provides us with split_view to tokenize strings, in a non-destructive manner: https://topanswers.xyz/cplusplus?q=749#a874
The previous methods cannot generate a tokenized vector in-place, meaning without abstracting them into a helper function they cannot initialize const vector<string> tokens. That functionality and the ability to accept any white-space delimiter can be harnessed using an istream_iterator. For example given: const string str{ "The quick \tbrown \nfox" } we can do this:
istringstream is{ str };
const vector<string> tokens{ istream_iterator<string>(is), istream_iterator<string>() };
Live Example
The required construction of an istringstream for this option has far greater cost than the previous 2 options, however this cost is typically hidden in the expense of string allocation.
If none of the above options are flexable enough for your tokenization needs, the most flexible option is using a regex_token_iterator of course with this flexibility comes greater expense, but again this is likely hidden in the string allocation cost. Say for example we want to tokenize based on non-escaped commas, also eating white-space, given the following input: const string str{ "The ,qu\\,ick ,\tbrown, fox" } we can do this:
const regex re{ "\\s*((?:[^\\\\,]|\\\\.)*?)\\s*(?:,|$)" };
const vector<string> tokens{ sregex_token_iterator(cbegin(str), cend(str), re, 1), sregex_token_iterator() };
Live Example
Check this example. It might help you..
#include <iostream>
#include <sstream>
using namespace std;
int main ()
{
string tmps;
istringstream is ("the dellimiter is the space");
while (is.good ()) {
is >> tmps;
cout << tmps << "\n";
}
return 0;
}
If you're using C++ ranges - the full ranges-v3 library, not the limited functionality accepted into C++20 - you could do it this way:
auto results = str | ranges::views::tokenize(" ",1);
... and this is lazily-evaluated. You can alternatively set a vector to this range:
auto results = str | ranges::views::tokenize(" ",1) | ranges::to<std::vector>();
this will take O(m) space and O(n) time if str has n characters making up m words.
See also the library's own tokenization example, here.
MFC/ATL has a very nice tokenizer. From MSDN:
CAtlString str( "%First Second#Third" );
CAtlString resToken;
int curPos= 0;
resToken= str.Tokenize("% #",curPos);
while (resToken != "")
{
printf("Resulting token: %s\n", resToken);
resToken= str.Tokenize("% #",curPos);
};
Output
Resulting Token: First
Resulting Token: Second
Resulting Token: Third
If you're willing to use C, you can use the strtok function. You should pay attention to multi-threading issues when using it.
For simple stuff I just use the following:
unsigned TokenizeString(const std::string& i_source,
const std::string& i_seperators,
bool i_discard_empty_tokens,
std::vector<std::string>& o_tokens)
{
unsigned prev_pos = 0;
unsigned pos = 0;
unsigned number_of_tokens = 0;
o_tokens.clear();
pos = i_source.find_first_of(i_seperators, pos);
while (pos != std::string::npos)
{
std::string token = i_source.substr(prev_pos, pos - prev_pos);
if (!i_discard_empty_tokens || token != "")
{
o_tokens.push_back(i_source.substr(prev_pos, pos - prev_pos));
number_of_tokens++;
}
pos++;
prev_pos = pos;
pos = i_source.find_first_of(i_seperators, pos);
}
if (prev_pos < i_source.length())
{
o_tokens.push_back(i_source.substr(prev_pos));
number_of_tokens++;
}
return number_of_tokens;
}
Cowardly disclaimer: I write real-time data processing software where the data comes in through binary files, sockets, or some API call (I/O cards, camera's). I never use this function for something more complicated or time-critical than reading external configuration files on startup.
You can simply use a regular expression library and solve that using regular expressions.
Use expression (\w+) and the variable in \1 (or $1 depending on the library implementation of regular expressions).
Many overly complicated suggestions here. Try this simple std::string solution:
using namespace std;
string someText = ...
string::size_type tokenOff = 0, sepOff = tokenOff;
while (sepOff != string::npos)
{
sepOff = someText.find(' ', sepOff);
string::size_type tokenLen = (sepOff == string::npos) ? sepOff : sepOff++ - tokenOff;
string token = someText.substr(tokenOff, tokenLen);
if (!token.empty())
/* do something with token */;
tokenOff = sepOff;
}
I thought that was what the >> operator on string streams was for:
string word; sin >> word;
Here's an approach that allows you control over whether empty tokens are included (like strsep) or excluded (like strtok).
#include <string.h> // for strchr and strlen
/*
* want_empty_tokens==true : include empty tokens, like strsep()
* want_empty_tokens==false : exclude empty tokens, like strtok()
*/
std::vector<std::string> tokenize(const char* src,
char delim,
bool want_empty_tokens)
{
std::vector<std::string> tokens;
if (src and *src != '\0') // defensive
while( true ) {
const char* d = strchr(src, delim);
size_t len = (d)? d-src : strlen(src);
if (len or want_empty_tokens)
tokens.push_back( std::string(src, len) ); // capture token
if (d) src += len+1; else break;
}
return tokens;
}
Seems odd to me that with all us speed conscious nerds here on SO no one has presented a version that uses a compile time generated look up table for the delimiter (example implementation further down). Using a look up table and iterators should beat std::regex in efficiency, if you don't need to beat regex, just use it, its standard as of C++11 and super flexible.
Some have suggested regex already but for the noobs here is a packaged example that should do exactly what the OP expects:
std::vector<std::string> split(std::string::const_iterator it, std::string::const_iterator end, std::regex e = std::regex{"\\w+"}){
std::smatch m{};
std::vector<std::string> ret{};
while (std::regex_search (it,end,m,e)) {
ret.emplace_back(m.str());
std::advance(it, m.position() + m.length()); //next start position = match position + match length
}
return ret;
}
std::vector<std::string> split(const std::string &s, std::regex e = std::regex{"\\w+"}){ //comfort version calls flexible version
return split(s.cbegin(), s.cend(), std::move(e));
}
int main ()
{
std::string str {"Some people, excluding those present, have been compile time constants - since puberty."};
auto v = split(str);
for(const auto&s:v){
std::cout << s << std::endl;
}
std::cout << "crazy version:" << std::endl;
v = split(str, std::regex{"[^e]+"}); //using e as delim shows flexibility
for(const auto&s:v){
std::cout << s << std::endl;
}
return 0;
}
If we need to be faster and accept the constraint that all chars must be 8 bits we can make a look up table at compile time using metaprogramming:
template<bool...> struct BoolSequence{}; //just here to hold bools
template<char...> struct CharSequence{}; //just here to hold chars
template<typename T, char C> struct Contains; //generic
template<char First, char... Cs, char Match> //not first specialization
struct Contains<CharSequence<First, Cs...>,Match> :
Contains<CharSequence<Cs...>, Match>{}; //strip first and increase index
template<char First, char... Cs> //is first specialization
struct Contains<CharSequence<First, Cs...>,First>: std::true_type {};
template<char Match> //not found specialization
struct Contains<CharSequence<>,Match>: std::false_type{};
template<int I, typename T, typename U>
struct MakeSequence; //generic
template<int I, bool... Bs, typename U>
struct MakeSequence<I,BoolSequence<Bs...>, U>: //not last
MakeSequence<I-1, BoolSequence<Contains<U,I-1>::value,Bs...>, U>{};
template<bool... Bs, typename U>
struct MakeSequence<0,BoolSequence<Bs...>,U>{ //last
using Type = BoolSequence<Bs...>;
};
template<typename T> struct BoolASCIITable;
template<bool... Bs> struct BoolASCIITable<BoolSequence<Bs...>>{
/* could be made constexpr but not yet supported by MSVC */
static bool isDelim(const char c){
static const bool table[256] = {Bs...};
return table[static_cast<int>(c)];
}
};
using Delims = CharSequence<'.',',',' ',':','\n'>; //list your custom delimiters here
using Table = BoolASCIITable<typename MakeSequence<256,BoolSequence<>,Delims>::Type>;
With that in place making a getNextToken function is easy:
template<typename T_It>
std::pair<T_It,T_It> getNextToken(T_It begin,T_It end){
begin = std::find_if(begin,end,std::not1(Table{})); //find first non delim or end
auto second = std::find_if(begin,end,Table{}); //find first delim or end
return std::make_pair(begin,second);
}
Using it is also easy:
int main() {
std::string s{"Some people, excluding those present, have been compile time constants - since puberty."};
auto it = std::begin(s);
auto end = std::end(s);
while(it != std::end(s)){
auto token = getNextToken(it,end);
std::cout << std::string(token.first,token.second) << std::endl;
it = token.second;
}
return 0;
}
Here is a live example: http://ideone.com/GKtkLQ
I know this question is already answered but I want to contribute. Maybe my solution is a bit simple but this is what I came up with:
vector<string> get_words(string const& text, string const& separator)
{
vector<string> result;
string tmp = text;
size_t first_pos = 0;
size_t second_pos = tmp.find(separator);
while (second_pos != string::npos)
{
if (first_pos != second_pos)
{
string word = tmp.substr(first_pos, second_pos - first_pos);
result.push_back(word);
}
tmp = tmp.substr(second_pos + separator.length());
second_pos = tmp.find(separator);
}
result.push_back(tmp);
return result;
}
Please comment if there is a better approach to something in my code or if something is wrong.
UPDATE: added generic separator
you can take advantage of boost::make_find_iterator. Something similar to this:
template<typename CH>
inline vector< basic_string<CH> > tokenize(
const basic_string<CH> &Input,
const basic_string<CH> &Delimiter,
bool remove_empty_token
) {
typedef typename basic_string<CH>::const_iterator string_iterator_t;
typedef boost::find_iterator< string_iterator_t > string_find_iterator_t;
vector< basic_string<CH> > Result;
string_iterator_t it = Input.begin();
string_iterator_t it_end = Input.end();
for(string_find_iterator_t i = boost::make_find_iterator(Input, boost::first_finder(Delimiter, boost::is_equal()));
i != string_find_iterator_t();
++i) {
if(remove_empty_token){
if(it != i->begin())
Result.push_back(basic_string<CH>(it,i->begin()));
}
else
Result.push_back(basic_string<CH>(it,i->begin()));
it = i->end();
}
if(it != it_end)
Result.push_back(basic_string<CH>(it,it_end));
return Result;
}
Here's my Swiss® Army Knife of string-tokenizers for splitting up strings by whitespace, accounting for single and double-quote wrapped strings as well as stripping those characters from the results. I used RegexBuddy 4.x to generate most of the code-snippet, but I added custom handling for stripping quotes and a few other things.
#include <string>
#include <locale>
#include <regex>
std::vector<std::wstring> tokenize_string(std::wstring string_to_tokenize) {
std::vector<std::wstring> tokens;
std::wregex re(LR"(("[^"]*"|'[^']*'|[^"' ]+))", std::regex_constants::collate);
std::wsregex_iterator next( string_to_tokenize.begin(),
string_to_tokenize.end(),
re,
std::regex_constants::match_not_null );
std::wsregex_iterator end;
const wchar_t single_quote = L'\'';
const wchar_t double_quote = L'\"';
while ( next != end ) {
std::wsmatch match = *next;
const std::wstring token = match.str( 0 );
next++;
if (token.length() > 2 && (token.front() == double_quote || token.front() == single_quote))
tokens.emplace_back( std::wstring(token.begin()+1, token.begin()+token.length()-1) );
else
tokens.emplace_back(token);
}
return tokens;
}
I wrote a simplified version (and maybe a little bit efficient) of https://stackoverflow.com/a/50247503/3976739 for my own use. I hope it would help.
void StrTokenizer(string& source, const char* delimiter, vector<string>& Tokens)
{
size_t new_index = 0;
size_t old_index = 0;
while (new_index != std::string::npos)
{
new_index = source.find(delimiter, old_index);
Tokens.emplace_back(source.substr(old_index, new_index-old_index));
if (new_index != std::string::npos)
old_index = ++new_index;
}
}
If the maximum length of the input string to be tokenized is known, one can exploit this and implement a very fast version. I am sketching the basic idea below, which was inspired by both strtok() and the "suffix array"-data structure described Jon Bentley's "Programming Perls" 2nd edition, chapter 15. The C++ class in this case only gives some organization and convenience of use. The implementation shown can be easily extended for removing leading and trailing whitespace characters in the tokens.
Basically one can replace the separator characters with string-terminating '\0'-characters and set pointers to the tokens withing the modified string. In the extreme case when the string consists only of separators, one gets string-length plus 1 resulting empty tokens. It is practical to duplicate the string to be modified.
Header file:
class TextLineSplitter
{
public:
TextLineSplitter( const size_t max_line_len );
~TextLineSplitter();
void SplitLine( const char *line,
const char sep_char = ',',
);
inline size_t NumTokens( void ) const
{
return mNumTokens;
}
const char * GetToken( const size_t token_idx ) const
{
assert( token_idx < mNumTokens );
return mTokens[ token_idx ];
}
private:
const size_t mStorageSize;
char *mBuff;
char **mTokens;
size_t mNumTokens;
inline void ResetContent( void )
{
memset( mBuff, 0, mStorageSize );
// mark all items as empty:
memset( mTokens, 0, mStorageSize * sizeof( char* ) );
// reset counter for found items:
mNumTokens = 0L;
}
};
Implementattion file:
TextLineSplitter::TextLineSplitter( const size_t max_line_len ):
mStorageSize ( max_line_len + 1L )
{
// allocate memory
mBuff = new char [ mStorageSize ];
mTokens = new char* [ mStorageSize ];
ResetContent();
}
TextLineSplitter::~TextLineSplitter()
{
delete [] mBuff;
delete [] mTokens;
}
void TextLineSplitter::SplitLine( const char *line,
const char sep_char /* = ',' */,
)
{
assert( sep_char != '\0' );
ResetContent();
strncpy( mBuff, line, mMaxLineLen );
size_t idx = 0L; // running index for characters
do
{
assert( idx < mStorageSize );
const char chr = line[ idx ]; // retrieve current character
if( mTokens[ mNumTokens ] == NULL )
{
mTokens[ mNumTokens ] = &mBuff[ idx ];
} // if
if( chr == sep_char || chr == '\0' )
{ // item or line finished
// overwrite separator with a 0-terminating character:
mBuff[ idx ] = '\0';
// count-up items:
mNumTokens ++;
} // if
} while( line[ idx++ ] );
}
A scenario of usage would be:
// create an instance capable of splitting strings up to 1000 chars long:
TextLineSplitter spl( 1000 );
spl.SplitLine( "Item1,,Item2,Item3" );
for( size_t i = 0; i < spl.NumTokens(); i++ )
{
printf( "%s\n", spl.GetToken( i ) );
}
output:
Item1
Item2
Item3