How do I separate the string into two , first one before ","or "." or " " etc and second one after that and then assign both of the to two different variables.
for example
string s="154558,ABCDEF; (This is to be inputted by the user ) string a = 154558; //It should be spilt like this after conversion string b =ABCDEF
I believe it can be something as simple as using rfind + substr
size_t pos = str.rfind('.')
new_str = str.substr(0, pos);
Essentially what the code is doing is searching for the first '.' and then using substr to extract the substring.
The two primary ways to split the string on ',' would be (1) create a std::basic_stringstream from the string and then use std::basic_istream::getline with the delimiter of ',' to separate the two strings, e.g.
#include <iostream>
#include <string>
#include <sstream>
int main (void) {
std::string s {"154558,ABCDEF"};
std::stringstream ss(s);
std::string sub {};
while (getline (ss, sub, ','))
std::cout << sub << '\n';
}
Example Use/Output
$ ./bin/str_split_ss
154558
ABCDEF
Or the second and equally easy way would be to use std::basic_string::find_first_of and find the position of ',' within the string and then use the position with std::basic_string::substr to extract the substring on either side of the comma, e.g.
#include <iostream>
#include <string>
int main (void) {
std::string s {"154558,ABCDEF"};
size_t pos = s.find_first_of (",");
if (pos != std::string::npos) {
std::cout << "first: " << s.substr(0, pos) <<
"\nsecond: " << s.substr(pos+1) << '\n';
}
}
Example Use/Output
$ ./bin/str_split_find_first_of
first: 154558
second: ABCDEF
Either way works fine. Look things over and let me know if you have further questions.
Related
Suppose i have a string as below
input = " \\PATH\MYFILES This is my sting "
output = MYFILES
from RHS when first char '\' is found get the word (ie MYFILES) and erase the rest.
Below is my approach i tired but its bad because there is a Runtime error as ABORTED TERMINATED WITH A CORE.
Please suggest cleanest and/or shortest way to get only a single word (ie MYFILES ) from the above string?
I have searching and try it from last two days but no luck .please help
Note: The input string in above example is not hardcoded as it ought to be .The string contain changes dynamically but char '\' available for sure.
std::regex const r{R"~(.*[^\\]\\([^\\])+).*)~"} ;
std::string s(R"(" //PATH//MYFILES This is my sting "));
std::smatch m;
int main()
{
if(std::regex_match(s,m,r))
{
std::cout<<m[1]<<endl;
}
}
}
To erase the part of a string, you have to find where is that part begins and ends. Finding somethig inside an std::string is very easy because the class have six buit-in methods for this (std::string::find_first_of, std::string::find_last_of, etc.). Here is a small example of how your problem can be solved:
#include <iostream>
#include <string>
int main() {
std::string input { " \\PATH\\MYFILES This is my sting " };
auto pos = input.find_last_of('\\');
if(pos != std::string::npos) {
input.erase(0, pos + 1);
pos = input.find_first_of(' ');
if(pos != std::string::npos)
input.erase(pos);
}
std::cout << input << std::endl;
}
Note: watch out for escape sequences, a single backslash is written as "\\" inside a string literal.
Let's say I have
string sentence{"Hello how are you."}
And I want string sentence to have "how are you" without the "Hello". How would I go about doing that.
I tried doing something like:
stringstream ss(sentence);
ss>> string junkWord;//to get rid of first word
But when I did:
cout<<sentence;//still prints out "Hello how are you"
It's pretty obvious that the stringstream doesn't change the actual string. I also tried using strtok but it doesn't work well with string.
Try the following
#include <iostream>
#include <string>
int main()
{
std::string sentence{"Hello how are you."};
std::string::size_type n = 0;
n = sentence.find_first_not_of( " \t", n );
n = sentence.find_first_of( " \t", n );
sentence.erase( 0, sentence.find_first_not_of( " \t", n ) );
std::cout << '\"' << sentence << "\"\n";
return 0;
}
The output is
"how are you."
str=str.substr(str.find_first_of(" \t")+1);
Tested:
string sentence="Hello how are you.";
cout<<"Before:"<<sentence<<endl;
sentence=sentence.substr(sentence.find_first_of(" \t")+1);
cout<<"After:"<<sentence<<endl;
Execution:
> ./a.out
Before:Hello how are you.
After:how are you.
Assumption is the line does not start with an empty space. In such a case this does not work.
find_first_of("<list of characters>").
the list of characters in our case is space and a tab. This will search for first occurance of any of the list of characters and return an iterator. After that adding +1 movers the position by one character.Then the position points to the second word of the line.
Substr(pos) will fetch the substring starting from position till the last character of the string.
You can for example take the remaining substring
string sentence{"Hello how are you."};
stringstream ss{sentence};
string junkWord;
ss >> junkWord;
cout<<sentence.substr(junkWord.length()+1); //string::substr
However, it also depends what you want to do further
There are countless ways to do this. I think I would go with this:
#include <iostream>
#include <string>
int main() {
std::string sentence{"Hello how are you."};
// First, find the index for the first space:
auto first_space = sentence.find(' ');
// The part of the string we want to keep
// starts at the index after the space:
auto second_word = first_space + 1;
// If you want to write it out directly, write the part of the string
// that starts at the second word and lasts until the end of the string:
std::cout.write(
sentence.data() + second_word, sentence.length() - second_word);
std::cout << std::endl;
// Or, if you want a string object, make a copy from the start of the
// second word. substr copies until the end of the string when you give
// it only one argument, like here:
std::string rest{sentence.substr(second_word)};
std::cout << rest << std::endl;
}
Of course, unless you have a really good reason not to, you should check that first_space != std::string::npos, which would mean the space was not found. The check is omitted in my sample code for clarity :)
You could use string::find() to locate the first space. Once you have its index, then get the sub string with string::substr() from the index after the index of the space up to the end of the string.
One liner:
std::string subStr = sentence.substr(sentence.find_first_not_of(" \t\r\n", sentence.find_first_of(" \t\r\n", sentence.find_first_not_of(" \t\r\n"))));
working example:
#include <iostream>
#include <string>
void main()
{
std::string sentence{ "Hello how are you." };
char whiteSpaces[] = " \t\r\n";
std::string subStr = sentence.substr(sentence.find_first_not_of(whiteSpaces, sentence.find_first_of(whiteSpaces, sentence.find_first_not_of(whiteSpaces))));
std::cout << subStr;
std::cin.ignore();
}
Here's how to use a stringstream to extract the junkword while ignoring any space before or after (using std::ws), then get the rest of the sentence, with robust error handling....
std::string sentence{"Hello how are you."};
std::stringstream ss{sentence};
std::string junkWord;
if (ss >> junkWord >> std::ws && std::getline(ss, sentence, '\0'))
std::cout << sentence << '\n';
else
std::cerr << "the sentence didn't contain ANY words at all\n";
See it running on ideone here....
#include <iostream> // cout
#include <string> // string
#include <sstream> // string stream
using namespace std;
int main()
{
string testString = "Hello how are you.";
istringstream iss(testString); // note istringstream NOT sstringstream
char c; // this will read the delima (space in this case)
string firstWord;
iss>>firstWord>>c; // read the first word and end after the first ' '
cout << "The first word in \"" << testString << "\" is \"" << firstWord << "\""<<endl;
cout << "The rest of the words is \"" <<testString.substr(firstWord.length()+1) << "\""<<endl;
return 0;
}
output
The first word in "Hello how are you." is "Hello"
The rest of the words is "how are you."
live testing at ideon
In a text file, I have several lines and each line looks like the below one (different numbers).
[275, 61],[279, 56],[285, 54],[292, 55],[298, 57],[315, 57],[321, 54],[328, 54],[335, 56]
When it comes to one line, I want to get each point separately.
For example:
first I should get [275, 61]
then I should get [279, 56]
and then [285, 54]
However when I tried the following;
istringstream linestream(line);
while (getline (linestream, item, ','))
{
...............
}
what it gives me is :
first [275
and then 61]
next [279
etc.
Can anyone tell me how to modify the while loop so that I get the required output ?
The behavior you see is the expected one since your delimiter is ','. If you want to delimit on every second ',' you need to concatenate your tokens back two by two.
For example "[275" + "," + " 61]"
Given your current output you should be able to do so with a simple for loop over your tokens.
The behaviour you are experiencing using getline is the correct one, since you are delimiting with ,.
In order to get the desired behaviour and if your compiler supports C++11 you could use the regular expressions library (i.e., regex) like the example below:
#include <iostream>
#include <string>
#include <regex>
int main() {
std::string str("[275, 61],[279, 56],[285, 54],[292, 55],[298, 57],[315, 57],[321, 54],[328, 54],[335, 56]");
std::regex e("\\[\\s*\\d+\\s*\\,\\s*\\d+\\s*\\]");
std::smatch sm;
std::regex_search(str, sm, e);
std::cout << "the matches were: ";
while (std::regex_search(str, sm, e)) {
for(auto x : sm) std::cout << x << " ";
std::cout << std::endl;
str = sm.suffix().str();
}
}
LIVE DEMO
Assuming that the text is coherent (no missed '[' or ']') You can manually search for position of '[' and position of ']', and then you can copy the sub-string between those for further analysis.
The following code demonstrate how you extract and print those sub-strings:
#include <stdio.h>
#include <string.h>
void main()
{
const char* test=" [275, 61],[279, 56],[285, 54],[292, 55],[298, 57],[315, 57],[321, 54],[328, 54],[335, 56] ";
char pair[20];
int i,pos1,pos2;
for (i=0,pos1=0,pos2=0; test[i]>0; i++)
{
if(test[i]=='[') pos1=i; //searching for '['
if(test[i]==']') pos2=i; //searching for ']'
//if(test[i]==']') printf("%.*s\n", pos2-pos1+1, test + pos1); //direct print from memory
if(test[i]==']') strncpy_s(pair,sizeof(pair), test + pos1, pos2-pos1+1); // copy result sub-string to "pair"
if(test[i]==']') printf("%s\n", pair); //print result on screen
}
}
I've been looking thousand of questions and answers about what I'm going to ask, but I still didn't find the way to do what I'm gonna to explain.
I have a text file from which I have to extract information about several things, all of them with the following format:
"string1":"string2"
And after that, there is more information, I mean:
The text file is something like this:
LINE 1
XXXXXXXXXXXXXXXXXXXXXXXXXXXX"string1":"string2"XXXXXXXXXXXXXXXXXXXXXXXXXX"string3":"string4"XXXXXXXXXXXXXXXXXXXXXXXXXXXX...('\n')
LINE 2
XXXXXXXXXXXXXXXXXXXXXXXXXXXX"string5":"string6"XXXXXXXXXXXXXXXXXXXXXXXXXX"string7":"string8"XXXXXXXXXXXXXXXXXXXXXXXXXXXX...
XXX represents irrelevant information I do not need, and theEntireString (string used in the code example) stores all the information of a single line, not all the information of the text file.
I have to find first the content of string1 and store the content of string2 into another string without the quotes. The problem is that I have to stop when I reache the last quote and I don't know how exactly do this. I suppose I have to use the functions find() and substr(), but despite having tried it repeatedly, I did not succeed.
What I have done is something like this:
string extractInformation(string theEntireString)
{
string s = "\"string1\":\"";
string result = theEntireString.find(s);
return result;
}
But this way I suppose I store into the string the last quote and the rest of the string.
"find" function just give you the position of matched string to get the resulting string you need to use the "subst" function. Try This
string start,end;
start = theEntireString.substr(1,theEntireString.find(":")-2);
end = theEntireString.substr(theEntireString.find(":")+2,theEntireString.size()-1);
That will solve you problem
Assuming either the key or value contains a quotation mark. The following will output the value after the ":". You can also use it in a loop to repeatedly extract the value field if you have multiple key-value pairs in the input string, provided that you keep a record of the position of last found instance.
#include <iostream>
using namespace std;
string extractInformation(size_t p, string key, const string& theEntireString)
{
string s = "\"" + key +"\":\"";
auto p1 = theEntireString.find(s);
if (string::npos != p1)
p1 += s.size();
auto p2 = theEntireString.find_first_of('\"',p1);
if (string::npos != p2)
return theEntireString.substr(p1,p2-p1);
return "";
}
int main() {
string data = "\"key\":\"val\" \"key1\":\"val1\"";
string res = extractInformation(0,"key",data);
string res1 = extractInformation(0,"key1",data);
cout << res << "," << res1 << endl;
}
Outputs:
val,val1
Two steps:
First we have to find the position of the : and splice the string into two parts:
string first = theEntireString.substr(0, theEntireString.find(":"));
string second = theEntireString.substr(theEntireString.find(":") + 1);
Now, we have to remove the "":
string final_first(first.begin() + 1, first.end() - 1);
string final_second(second.begin() + 1, second.end() - 1);
You don't need any string operation. I hope the XXXXX doesn't contain any '"', so You can read the both strings directly from the file:
ifstream file("input.txt");
for( string s1,s2; getline( getline( file.ignore( numeric_limits< streamsize >::max(), '"' ), s1, '"' ) >> Char<':'> >> Char<'"'>, s2, '"' ); )
cout << "S1=" << s1 << " S2=" << s2 << endl;
the little help-function Char is:
template< char C >
std::istream& Char( std::istream& in )
{
char c;
if( in >> c && c != C )
in.setstate( std::ios_base::failbit );
return in;
}
#include <regex>
#include <iostream>
using namespace std;
const string text = R"(
XXXXXXXXXXXXXXXXXXXXXXXXXXXX"string1":"string2"XXXXXXXXXXXXXXXXXXXXXXXXXX"string3" :"string4" XXXXXXXXXXXXXXXXXXXXXXXXXXXX...
XXXXXXXXXXXXXXXXXXXXXXXXXXXX"string5": "string6"XXXXXXXXXXXXXXXXXXXXXXXXXX"string7" : "string8" XXXXXXXXXXXXXXXXXXXXXXXXXXXX...
)";
int main() {
const regex pattern{R"~("([^"]*)"\s*:\s*"([^"]*)")~"};
for (auto it = sregex_iterator(begin(text), end(text), pattern); it != sregex_iterator(); ++it) {
cout << it->format("First: $1, Second: $2") << endl;
}
}
Output:
First: string1, Second: string2
First: string3, Second: string4
First: string5, Second: string6
First: string7, Second: string8
Running (with clang and libc++): http://coliru.stacked-crooked.com/a/f0b5fd383bc227fc
This is how raw string literals look in an editor that understand them: http://bl.ocks.org/anonymous/raw/9442865/
I have a string str ( "1 + 2 = 3" ). I want to obtain the individual numbers of the string in their decimal values( not ASCII ). I have tried atoi and c_str(). But both them require the entire string to consist of only numbers. I am writing my code in C++.
Any help would be great.
My challenge is to evaluate a prefix expression. I am reading from a file where each line contains a prefix expression. My code snippet to tokenize and and store the variables is as shown below. Each line of the file contains numbers and operators(+,-,*) which are separated by a space.
Ex - line = ( * + 2 3 4);
ifstream file;
string line;
file.open(argv[1]);
while(!file.eof())
{
getline(file,line);
if(line.length()==0)
continue;
else
{
vector<int> vec;
string delimiters = " ";
size_t current;
size_t next = -1;
do
{
current = next + 1;
next = line.find_first_of( delimiters, current );
if((line[next] <=57)&&(line[next] >=48))
vec.push_back(atoi((line.substr( current, next - current )).c_str()));
}while (next != string::npos);
cout << vec[0] << endl;
}
}
file.close();
In this case vec[0] prints 50 not 2.
You need to learn to delimit a string. Your delimiting characters would be mathematical operators (ie:
C: creating array of strings from delimited source string
http://www.gnu.org/software/libc/manual/html_node/Finding-Tokens-in-a-String.html
In the case of the second link, you would do something like:
const char delimiters[] = "+-=";
With this knowledge, you can create an array of strings, and call atoi() on each string to get the numeric equivalent. Then you can use the address (array index) of each delimiter to determine which operator is there.
For just things like addition and subtraction, this will be dead simple. If you want order of operations and multiplication, parentheses, etc, your process flow logic will be more complicated.
For a more in-depth example, please see this final link. A simple command-line calculator in C. That should make it crystal clear.
http://stevehanov.ca/blog/index.php?id=26
You will not fall into your if, since your next position will be at a delimiter.
string delimiters = " ";
...
next = line.find_first_of( delimiters, current );
if((line[next] <=57)&&(line[next] >=48))
...
Since your delimiters consist of " ", then line[next] will be a space character.
From the description of your problem, you are missing code that will save away your operators. There is no code to attempt to find the operators.
You don't have to assume ASCII for testing for a digit. You can use is_digit() for example, or you can compare against '9' and '0'.
When you print your vector element, you may be accessing the vector inappropriately, because no item may have ever been inserted into the array.
Don't use fin.eof() to control a loop. That function is only useful after a read has failed.
There are a number of ways to get ints from a std::string, I'm choosing std::stoi() from the C++11 standard in this case.
#include <fstream>
#include <iostream>
#include <iterator>
#include <sstream>
#include <string>
#include <vector>
typedef std::vector<int> ints;
bool is_known_operator(std::string const& token)
{
static char const* tokens[] = {"*", "/", "+", "-"};
return std::find(std::begin(tokens), std::end(tokens), token) != std::end(tokens);
}
ints tokenise(std::string const& line)
{
ints vec;
std::string token;
std::istringstream iss(line);
while (iss >> token)
{
if (is_known_operator(token))
{
std::cout << "Handle operator [" << token << "]" << std::endl;
}
else
{
try
{
auto number = std::stoi(token);
vec.push_back(number);
}
catch (const std::invalid_argument&)
{
std::cerr << "Unexpected item in the bagging area ["
<< token << "]" << std::endl;
}
}
}
return vec;
}
int main(int, const char *argv[])
{
std::ifstream file(argv[1]);
std::string line;
ints vec;
while (std::getline(file, line))
{
vec = tokenise(line);
}
std::cout << "The following " << vec.size() << " numbers were read:\n";
std::copy(vec.begin(), vec.end(), std::ostream_iterator<int>(std::cout, "\n"));
}