Split a string into an array in C++

Question

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How to split a string in C++?

I have an input file of data and each line is an entry. in each line each "field" is seperated by a white space " " so I need to split the line by space. other languages have a function called split (C#, PHP etc) but I cant find one for C++. How can I achieve this? Here is my code that gets the lines:

string line;
ifstream in(file);

while(getline(in, line)){

  // Here I would like to split each line and put them into an array

}

score 23 · Accepted Answer · edited May 23 '17 at 11:46

23

#include <sstream>  //for std::istringstream
#include <iterator> //for std::istream_iterator
#include <vector>   //for std::vector

while(std::getline(in, line))
{
    std::istringstream ss(line);
    std::istream_iterator<std::string> begin(ss), end;

    //putting all the tokens in the vector
    std::vector<std::string> arrayTokens(begin, end); 

    //arrayTokens is containing all the tokens - use it!
}

By the way, use qualified-names such as std::getline, std::ifstream like I did. It seems you've written using namespace std somewhere in your code which is considered a bad practice. So don't do that:

Why is "using namespace std" considered bad practice?

edited May 23 '17 at 11:46

Community

1
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answered Dec 09 '11 at 16:03

Nawaz

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Can you provide a link to a discussion on why it is a bad practise to use `using namespace x`? – jli Dec 09 '11 at 16:12
@jli: Added the link to my answer. See it. – Nawaz Dec 09 '11 at 16:13
2

@Nawaz thanks, Looking at my other questions, the syntax I am using and the way I am learning C++ from my instructors at uni is highly questionable :S!!!!! – Ahoura Ghotbi Dec 09 '11 at 16:29

score 6 · Answer 2 · answered Dec 09 '11 at 16:03

6

vector<string> v;
boost::split(v, line, ::isspace);

http://www.boost.org/doc/libs/1_48_0/doc/html/string_algo/usage.html#id3115768

answered Dec 09 '11 at 16:03

Benjamin Lindley

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score 5 · Answer 3 · edited Nov 16 '18 at 09:49

5

I have written a function for a similar requirement of mine, maybe you can use it!

std::vector<std::string> &split(const std::string &s, char delim, std::vector<std::string> &elems) 
{
    std::stringstream ss(s+' ');
    std::string item;
    while(std::getline(ss, item, delim)) 
    {
        elems.push_back(item);
    }
    return elems;
}

edited Nov 16 '18 at 09:49

Newbyte

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answered Dec 09 '11 at 16:07

Vijay

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score 3 · Answer 4 · edited Apr 13 '16 at 22:57

3

Try strtok. Look for it in the C++ reference:.

edited Apr 13 '16 at 22:57

pppery

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answered Dec 09 '11 at 16:04

LucianMLI

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`strtok` is a C library thing, whereas the poster is asking for how to do it correctly with C++. – jli Dec 09 '11 at 16:08
2

and c++ is not c?(... OMG all those years they all lied to me :D). Since when c library have stopped working in c++(or turned incorrect)? – LucianMLI Dec 12 '11 at 08:58
If you mix them, you add unnecessary dependances, among other issues. – jli Dec 12 '11 at 14:34
A link to the issues and DEPENDENCIES involved in using c in c++ please? ...I mean for all those years of wrongly compiling and using c code and libraries in c++ . – LucianMLI Dec 12 '11 at 18:21
http://stackoverflow.com/questions/4025869/using-mixing-c-in-c-code I guess the dependencies is not really the issue, but imo doing something like `#include ` `#include ` gets redundant. – jli Dec 12 '11 at 18:29
Also I just realized I spelled dependencies wrong in my second comment (damn phone soft keyboards). – jli Dec 12 '11 at 18:32

score 1 · Answer 5 · answered Dec 09 '11 at 16:11

The code below uses strtok() to split a string into tokens and stores the tokens in a vector.

#include <iostream>
#include <algorithm>
#include <vector>
#include <string>

using namespace std;


char one_line_string[] = "hello hi how are you nice weather we are having ok then bye";
char seps[]   = " ,\t\n";
char *token;



int main()
{
   vector<string> vec_String_Lines;
   token = strtok( one_line_string, seps );

   cout << "Extracting and storing data in a vector..\n\n\n";

   while( token != NULL )
   {
      vec_String_Lines.push_back(token);
      token = strtok( NULL, seps );
   }
     cout << "Displaying end result in  vector line storage..\n\n";

    for ( int i = 0; i < vec_String_Lines.size(); ++i)
    cout << vec_String_Lines[i] << "\n";
    cout << "\n\n\n";


return 0;
}

score 0 · Answer 6 · edited Dec 09 '11 at 16:20

0

C++ is best used with the almost-standard-library boost.

And an example : http://www.boost.org/doc/libs/1_48_0/doc/html/string_algo/usage.html#id3115768

edited Dec 09 '11 at 16:20

Flexo

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answered Dec 09 '11 at 16:03

Tristram Gräbener

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jli · Answer 7 · 2011-12-09T16:28:42.050

0

Either use a stringstream or read token by token from your ifstream.

To do it with a stringstream:

string line, token;
ifstream in(file);

while(getline(in, line))
{
    stringstream s(line);
    while (s >> token)
    {
        // save token to your array by value
    }
}

edited Dec 09 '11 at 16:28

answered Dec 09 '11 at 16:03

jli

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Of course you could use boost if you so desire, or another STL function to do the copying out of the stringstream. – jli Dec 09 '11 at 16:10
If the input ends in whitespace, this inner while-loop generates an additional empty token in the end. The idiomatic C++ `while(s >> token)` does not. – Cubbi Dec 09 '11 at 16:27
This is true. May as well edit to use that method. – jli Dec 09 '11 at 16:28

Split a string into an array in C++

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