Getting this error currently:
main.cpp: In function ‘std::string class_name(const std::type_info&)’:
main.cpp:43:45: error: ‘pos’ was not declared in this scope
if (const size_t pos = name.find(prefix)); pos != string::npos)
I've been trying to mess around with this string but can't seem to get it to pass when I try to compile.
The code:
#include <string>
#include <map>
#include <array>
#include <vector>
#include <iostream>
#include <iomanip>
#include <sstream>
#include <typeinfo>
using namespace std;
void horizontal_line(size_t n = 80)
{
cout << endl << string(n, '-');
}
void pause(size_t n = 80)
{
horizontal_line(n);
cout << "\n[Enter] to continue.";
cin.get();
}
string currency(const float& amount)
{
ostringstream ss;
ss.imbue(std::locale(""));
ss << showbase << put_money(amount * 100);
return ss.str();
}
string class_name(const type_info& typeinfo)
{
static const string prefix("class ");
static const size_t length = prefix.size();
string name(typeinfo.name ());
if (const size_t pos = name.find(prefix)); pos != string::npos)
name.erase(pos, length);
return name;
}
Trying to get it to compile to show the output for a vehicle list but having some trouble with this portion, the output obviously wont compile at the moment with this error. (Obviously this isn't the full code)
The syntax you are trying to use to declare AND initialize pos inside the if statement:
if (const size_t pos = name.find(prefix)); pos != string::npos)
Is valid only in C++17 and later. Also, you have an erroneous ) before the ; that you need to remove, the correct statement is:
if (const size_t pos = name.find(prefix); pos != string::npos)
For earlier versions of C++, you need to separate the declaration of pos from the if statement:
const size_t pos = name.find(prefix);
if (pos != string::npos)
Alternatively, you can perform the assignment of pos inside the if statement, just not the declaration, however the syntax is slightly different:
size_t pos;
if ((pos = name.find(prefix)) != string::npos)
If I understand your code correctly, this is probably what you meant to do:
size_t pos = name.find(prefix);
if(pos != string::npos)
name.erase(pos, length);
You’ve a semicolon directly after the if. So the 2nd time pos appears, it’s not in an if block which is the only place pos would be in scope.
Related
I've been looking for ways to count the number of words in a string, but specifically for strings that may contain typos (i.e. "_This_is_a___test" as opposed to "This_is_a_test"). Most of the pages I've looked at only handle single spaces.
This is actually my first time programming in C++, and I don't have much other programming experience to speak of (2 years of college in C and Java). Although what I have is functional, I'm also aware it's complex, and I'm wondering if there is a more efficient way to achieve the same results?
This is what I have currently. Before I run the string through numWords(), I run it through a trim function that removes leading whitespace, then check that there are still characters remaining.
int numWords(string str) {
int count = 1;
for (int i = 0; i < str.size(); i++) {
if (str[i] == ' ' || str[i] == '\t' || str[i] == '\n') {
bool repeat = true;
int j = 1;
while (j < (str.size() - i) && repeat) {
if (str[i + j] != ' ' && str[i + j] != '\t' && str[i + j] != '\n') {
repeat = false;
i = i + j;
count++;
}
else
j++;
}
}
}
return count;
}
Also, I wrote mine to take a string argument, but most of the examples I've seen used (char* str) instead, which I wasn't sure how to use with my input string.
You don't need all those stringstreams to count word boundary
#include <string>
#include <cctype>
int numWords(std::string str)
{
bool space = true; // not in word
int count = 0;
for(auto c:str){
if(std::isspace(c))space=true;
else{
if(space)++count;
space=false;
}
}
return count;
}
One solution is to utilize std::istringstream to count the number of words and to skip over spaces automatically.
#include <sstream>
#include <string>
#include <iostream>
int numWords(std::string str)
{
int count = 0;
std::istringstream strm(str);
std::string word;
while (strm >> word)
++count;
return count;
}
int main()
{
std::cout << numWords(" This is a test ");
}
Output:
4
Albeit as mentioned std::istringstream is more "heavier" in terms of performance than writing your own loop.
Sam's comment made me write a function that does not allocate strings for words. But just creates string_views on the input string.
#include <cassert>
#include <cctype>
#include <vector>
#include <string_view>
#include <iostream>
std::vector<std::string_view> get_words(const std::string& input)
{
std::vector<std::string_view> words;
// the first word begins at an alpha character
auto begin_of_word = std::find_if(input.begin(), input.end(), [](const char c) { return std::isalpha(c); });
auto end_of_word = input.begin();
auto end_of_input = input.end();
// parse the whole string
while (end_of_word != end_of_input)
{
// as long as you see text characters move end_of_word one back
while ((end_of_word != end_of_input) && std::isalpha(*end_of_word)) end_of_word++;
// create a string view from begin of word to end of word.
// no new string memory will be allocated
// std::vector will do some dynamic memory allocation to store string_view (metadata of word positions)
words.emplace_back(begin_of_word, end_of_word);
// then skip all non readable characters.
while ((end_of_word != end_of_input) && !std::isalpha(*end_of_word) ) end_of_word++;
// and if we haven't reached the end then we are at the beginning of a new word.
if ( end_of_word != input.end()) begin_of_word = end_of_word;
}
return words;
}
int main()
{
std::string input{ "This, this is a test!" };
auto words = get_words(input);
for (const auto& word : words)
{
std::cout << word << "\n";
}
return 0;
}
You can use standard function std::distance with std::istringstream the following way
#include <iostream>
#include <sstream>
#include <string>
#include <iterator>
int main()
{
std::string s( " This is a test" );
std::istringstream iss( s );
auto count = std::distance( std::istream_iterator<std::string>( iss ),
std::istream_iterator<std::string>() );
std::cout << count << '\n';
}
The program output is
4
If you want you can place the call of std::distance in a separate function like
#include <iostream>
#include <sstream>
#include <string>
#include <iterator>
size_t numWords( const std::string &s )
{
std::istringstream iss( s );
return std::distance( std::istream_iterator<std::string>( iss ),
std::istream_iterator<std::string>() );
}
int main()
{
std::string s( " This is a test" );
std::cout << numWords( s ) << '\n';
}
If separators can include other characters apart from white space characters as for example punctuations then you should use methods of the class std::string or std::string_view find_first_of and find_first_not_of.
Here is a demonstration program.
#include <iostream>
#include <string>
#include <string_view>
size_t numWords( const std::string_view s, std::string_view delim = " \t" )
{
size_t count = 0;
for ( std::string_view::size_type pos = 0;
( pos = s.find_first_not_of( delim, pos ) ) != std::string_view::npos;
pos = s.find_first_of( delim, pos ) )
{
++count;
}
return count;
}
int main()
{
std::string s( "Is it a test ? Yes ! Now we will run it ..." );
std::cout << numWords( s, " \t!?.," ) << '\n';
}
The program output is
10
you can do it easily with regex
int numWords(std::string str)
{
std::regex re("\\S+"); // or `[^ \t\n]+` to exactly match the question
return std::distance(
std::sregex_iterator(str.begin(), str.end(), re),
std::sregex_iterator()
);
}
I want to split the strings on each line of my text file into an array, similar to the split() function in python. my desired syntax is a loop that enters every split-string into the next index of an array,
so for example if my string:
"ab,cd,ef,gh,ij"
, every time I encounter a comma then I would:
datafile >> arr1[i]
and my array would end up:
arr1 = [ab,cd,ef,gh,ij]
a mock code without reading a text file is provided below
#include <iostream>
#include <fstream>
#include <stdio.h>
#include <string.h>
#include <string>
using namespace std;
int main(){
char str[] = "ab,cd,ef,gh,ij"; //" ex str in place of file contents/fstream sFile;"
const int NUM = 5;
string sArr[NUM];//empty array
char *token = strtok(str, ",");
for (int i=0; i < NUM; i++)
while((token!=NULL)){
("%s\n", token) >> sArr[i];
token = strtok(NULL, ",");
}
cout >> sArr;
return 0;
}
In C++ you can read a file line by line and directly get a std::string.
You will found below an example I made with a split() proposal as you requested, and a main() example of reading a file:
Example
data file:
ab,cd,ef,gh
ij,kl,mn
c++ code:
#include <fstream>
#include <iostream>
#include <vector>
std::vector<std::string> split(const std::string & s, char c);
int main()
{
std::string file_path("data.txt"); // I assumed you have that kind of file
std::ifstream in_s(file_path);
std::vector <std::vector<std::string>> content;
if(in_s)
{
std::string line;
std::vector <std::string> vec;
while(getline(in_s, line))
{
for(const std::string & str : split(line, ','))
vec.push_back(str);
content.push_back(vec);
vec.clear();
}
in_s.close();
}
else
std::cout << "Could not open: " + file_path << std::endl;
for(const std::vector<std::string> & str_vec : content)
{
for(unsigned int i = 0; i < str_vec.size(); ++i)
std::cout << str_vec[i] << ((i == str_vec.size()-1) ? ("") : (" : "));
std::cout << std::endl;
}
return 0;
}
std::vector<std::string> split(const std::string & s, char c)
{
std::vector<std::string> splitted;
std::string word;
for(char ch : s)
{
if((ch == c) && (!word.empty()))
{
splitted.push_back(word);
word.clear();
}
else
word += ch;
}
if(!word.empty())
splitted.push_back(word);
return splitted;
}
output:
ab : cd : ef : gh
ij : kl : mn
I hope it will help.
So, a few things to fix. Firstly, arrays and NUM are kind of limiting - you have to fix up NUM whenever you change the input string, so C++ provides std::vector which can resize itself to however many strings it finds. Secondly, you want to call strtok until it returns nullptr once, and you can do that with one loop. With both your for and NUM you call strtok too many times - even after it has returned nullptr. Next, to put the token into a std::string, you would assign using my_string = token; rather than ("%s\n", token) >> my_string - which is a broken mix of printf() formatting and C++ streaming notation. Lastly, to print the elements you've extracted, you can use another loop. All these changes are illustrated below.
char str[] = "ab,cd,ef,gh,ij";
std::vector<std::string> strings;
char* token = strtok(str, ",");
while ((token != nullptr))
{
strings.push_back(token);
token = strtok(NULL, ",");
}
for (const auto& s : strings)
cout >> s >> '\n';
Your code is overly complicated and wrong.
You probably want this:
#include <iostream>
#include <string>
#include <string.h>
using namespace std;
int main() {
char str[] = "ab,cd,ef,gh,ij"; //" ex str in place of file contents/fstream sFile;"
const int NUM = 5;
string sArr[NUM];//empty array
char *token = strtok(str, ",");
int max = 0;
while ((token != NULL)) {
sArr[max++] = token;
token = strtok(NULL, ",");
}
for (int i = 0; i < max; i++)
cout << sArr[i] << "\n";
return 0;
}
This code is still poor and no bound checking is done.
But anyway, you should rather do it the C++ way as suggested in the other answers.
Use boost::split
#include <boost/algorithm/string.hpp>
[...]
std::vector<std::string> strings;
std::string val("ab,cd,ef,gh,ij");
boost::split(strings, val, boost::is_any_of(","));
You could do something like this
std::string str = "ab,cd,ef,gh,ij";
std::vector<std::string> TokenList;
std::string::size_type lastPos = 0;
std::string::size_type pos = str.find_first_of(',', lastPos);
while(pos != std::string::npos)
{
std::string temp(str, lastPos, pos - lastPos);
TokenList.push_back(temp);
lastPos = pos + 1;
pos = str.find_first_of(',', lastPos);
}
if(lastPos != str.size())
{
std::string temp(str, lastPos, str.size());
TokenList.push_back(temp);
}
for(int i = 0; i < TokenList.size(); i++)
std::cout << TokenList.at(i) << std::endl;
I want to split a string by any occurrence of and.
First of all I have to make it clear that I do not intend to use any regex as a delimiter.
I run the following code:
#include <iostream>
#include <regex>
#include <boost/algorithm/string.hpp>
int main()
{
std::vector<std::string> results;
std::string text=
"Alexievich, Svetlana and Lindahl,Tomas and Campbell,William";
boost::split(
results,
text,
boost::is_any_of(" and "),
boost::token_compress_off
);
for(auto result:results)
{
std::cout<<result<<"\n";
}
return 0;
}
and the results are different from what I expect:
Alexievich,
Svetl
Li
hl,Tom
s
C
mpbell,Willi
m
It seems every character in the delimiter acts separately while I need to have the whole and as a delimiter.
Please do not link to this boost example unless you are sure that it will work for my case.
<algorithm> contains search - right tool for this task.
vector<string> results;
const string text{ "Alexievich, Svetlana and Lindahl,Tomas and Campbell,William" };
const string delim{ " and " };
for (auto p = cbegin(text); p != cend(text); ) {
const auto n = search(p, cend(text), cbegin(delim), cend(delim));
results.emplace_back(p, n);
p = n;
if (cend(text) != n) // we found delim, skip over it.
p += delim.length();
}
The old-fashioned way:
#include <iostream>
#include <string>
#include <vector>
int main()
{
std::vector<std::string> results;
std::string text=
"Alexievich, Svetlana and Lindahl,Tomas and Campbell,William";
size_t pos = 0;
for (;;) {
size_t next = text.find("and", pos);
results.push_back(text.substr(pos, next - pos));
if (next == std::string::npos) break;
pos = next + 3;
}
for(auto result:results)
{
std::cout<<result<<"\n";
}
return 0;
}
Packaging into a reusable function is left as an exercise for the reader.
I was trying to create a program to calculate the simplified version of a polynomial expression. I want to separate all of the variables, and constants (with plus signs) but my program seems to not be recognizing some of the plus signs in my string:
string al("2x+2+6y+8^7");
vector<string> variableStorage;
for (auto &c : al)
{
static int count = 0;
static int lastcount = 0;
if(c == '+' || count == al.length()-1)
{
static int spot(0);
variableStorage.push_back(al.substr(lastcount, count));
lastcount = count+1;
++spot;
}
++count;
}
for(auto c : variableStorage)
cout << c << endl;
When I run this program, I get the following output:
2x
2+6y
6y+8^7
8^7
But my desired output is:
2x
2
6y
8^7
I tried checking my math for any mistakes, but it seems good as far as I can see.
Split the string (tokenize) at the +s
#include <string>
#include <vector>
using namespace std;
// This code from another SO question about splitting strings in C++
// http://stackoverflow.com/questions/236129/how-to-split-a-string-in-c
template < class ContainerT >
void tokenize(const std::string& str, ContainerT& tokens,
const std::string& delimiters = " ", bool trimEmpty = false)
{
std::string::size_type pos, lastPos = 0;
while(true)
{
pos = str.find_first_of(delimiters, lastPos);
if(pos == std::string::npos)
{
pos = str.length();
if(pos != lastPos || !trimEmpty)
tokens.push_back(ContainerT::value_type(str.data()+lastPos,
(ContainerT::value_type::size_type)pos-lastPos ));
break;
}
else
{
if(pos != lastPos || !trimEmpty)
tokens.push_back(ContainerT::value_type(str.data()+lastPos,
(ContainerT::value_type::size_type)pos-lastPos ));
}
lastPos = pos + 1;
}
};
int main( void )
{
string al("2x+2+6y+8^7");
vector<string> variableStorage;
tokenize( al, viariableStorage );
for(auto c : variableStorage)
cout << c << endl;
//Your items are in variableStorage at this point
return( 0 );
}
The code above is not tested, it's late and I'm feeling lazy. I hope it gets the concept across.
substr takes starting position and length. So you should be calling al.substr(lastcount, count-lastcount)
Is there any inbuilt function available to get strings between two delimiter string in C++?
Input string
(23567)=(58765)+(67888)+(65678)
Expected Output
23567
58765
67888
65678
include <iostream>
#include <stdexcept>
#include <string>
#include <sstream>
#include <vector>
std::vector<std::string> tokenize(const std::string& input)
{
std::vector<std::string> result;
std::istringstream stream(input);
std::string thingie; // please choose a better name, my inspiration is absent today
while(std::getline(stream, thingie, '('))
{
if(std::getline(stream, thingie, ')'))
result.push_back(thingie);
else
throw std::runtime_error("expected \')\' to match \'(\'.");
}
return result;
}
void rtc()
{
ifstream myfile(test.txt);
if(myfile.is_open())
while (!myfile.eof())
{
getline(myfile,line);
auto tokens = tokenize(line);
for(auto&& item : tokens)
std::cout << item << '\n';
}
Error C4430 missing type specifier int assumed note:c++ does not support default int
ErrorC2440initializing cannot convertfrom std::vector<_ty>to int
Error C2059syntac error empty declaration
Error C2143syntax error missing;before&&
Error C2059syntax error:')'
Use std::getline:
#include <iostream>
#include <stdexcept>
#include <string>
#include <sstream>
#include <vector>
std::vector<std::string> tokenize(const std::string& input)
{
std::vector<std::string> result;
std::istringstream stream(input);
std::string thingie; // please choose a better name, my inspiration is absent today
while(std::getline(stream, thingie, '('))
{
if(std::getline(stream, thingie, ')'))
result.push_back(thingie);
else
throw std::runtime_error("expected \')\' to match \'(\'.");
}
return result;
}
int main()
{
std::string test = "(23567)=(58765)+(67888)+(65678)";
auto tokens = tokenize(test);
for(auto&& item : tokens)
std::cout << item << '\n';
}
Live example here.
For those not entirely convinced by the awesome robustness of this solution, I specialized this for double inputs between the parentheses, and used boost::lexical_cast to verify the input:
#include <iostream>
#include <stdexcept>
#include <string>
#include <sstream>
#include <vector>
#include <boost/lexical_cast.hpp>
std::vector<double> tokenize(const std::string& input)
{
std::vector<double> result;
std::istringstream stream(input);
std::string thingie; // please choose a better name, my inspiration is absent today
while(std::getline(stream, thingie, '('))
{
if(std::getline(stream, thingie, ')'))
{
try
{
result.push_back(boost::lexical_cast<double>(thingie));
}
catch(...)
{
throw std::runtime_error("This wasn't just a number, was it?");
}
}
else
throw std::runtime_error("expected \')\' to match \'(\'.");
}
return result;
}
int main()
{
std::string test = "(23567)=(58765)+(67888)+(65678)";
auto tokens = tokenize(test);
for(auto&& item : tokens)
std::cout << item << '\n';
test = "(2h567)=(58765)+(67888)+(65678)";
tokens = tokenize(test);
}
Live example here. Now go cry about how bad strtok really is, or how bad/unportable the general <regex> implementations are currently. Also, for those who doubt boost::lexical_cast performance-wise, please see the results for yourself.
strpbrk can be used to find the start of each token
or strcspn can be used to count the characters until the next token
then strspn can be used to find the length of each token.
const char tokenChars[] = "0123456789";
char token = input; // say input is "(23567)=(58765)+(67888)+(65678)"
while( 0 != (token = strpbrk( token, tokenChars )) ) // find token
{
size_t tokenLen = strspn( token, token_chars ); // find length of token
// print out tokenLen characters of token here!
token+= tokenLen; // go to end of token
}
http://www.cplusplus.com/reference/cstring/strspn/
http://www.cplusplus.com/reference/cstring/strcspn/
http://www.cplusplus.com/reference/cstring/strpbrk/
Here's the answer if you wanna use pointers:
char test[32] = "(23567)=(58765)+(67888)+(65678)";
char *output = NULL;
char *pos = (char *)test;
int length = 0;
while (*pos != '\0') {
if(*pos == '(' || *pos == ')' || *pos == '+' || *pos == '=') {
*pos = '\0';
if (length > 0) {
output = new char[length + 1];
strncpy_s(output, length + 1, pos - length, length + 1);
length = 0;
cout << output << endl;
delete [] output;
output = NULL;
}
} else {
length++;
}
pos++;
}
While some of the commentators may hate it I like this:
for (p = std::strtok(input, "+"); p != NULL; p = std::strtok(NULL, "+"))
{
// do more stuff
}
This won't work off the bat - the delimiters need expanding - it demonstrates the ease of use.
const char input[] = "(2av67q)=(ble ble)+(67888)+(qpa)";
int s = 0;
for(int i = 0; input[i]; i++)
{
if ( input[i] == ')' )
{
cout << endl;
s = 0;
}
else if ( input[i] == '(' )
{
s = 1;
continue;
}
else
{
if ( s == 1 )
{
cout << input[i];
}
}
}
result:
2av67q
ble ble
67888
qpa
Here is a solution using a regular expression:
std::vector<std::string> get_numbers(std::string const& s)
{
static std::regex regex(R"(^\((\d+)\)=\((\d+)\)(?:\+\((\d+)\))+$)",
std::regex_constants::ECMAScript
| std::regex_constants::optimize);
std::vector<std::string> results;
std::sregex_iterator matches(s.cbegin(), s.cend(), regex);
for (auto first = matches->cbegin(), last = matches->cend();
last != first;
++first)
{
results.push_back(first->str());
}
return results;
}