How to split a space separated string into multiple strings in C++?

Question

Somewhat my code looks like below:

static int myfunc(const string& stringInput)
{
    string word;
    stringstream ss;

    ss << stringInput;
    while(ss >> word)
    {
        ++counters[word];
    }
    ...
}

The purpose here is to get an input string (separated by white space ' ') into the string variable word, but the code here seems to have a lot of overhead -- convert the input string to a string stream and read from the string stream into the target string.

Is there a more elegant way to accomplish the same purpose?

I think this question has been asked a few times already: stackoverflow.com/questions/1894886/… stackoverflow.com/questions/4328685/… stackoverflow.com/questions/536148/… stackoverflow.com/questions/1511029/… stackoverflow.com/questions/3162108/… — Jared Krumsie
– Jared Krumsie, Commented Dec 30, 2011 at 20:23
Thank you, sixletter and Jared. Your threads provided me with a lot of good knowledge on this topic. Sorry I didn't do a thorough search in this forum before posting. Thanks again! — Qiang Xu
– Qiang Xu, Commented Dec 30, 2011 at 20:33

alex tingle · Accepted Answer · 2011-12-30 19:58:52Z

4

You are asking how to split a string. Boost has a helpful utility boost::split()

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

Here's an example that puts the resulting words into a vector:

#include <boost/algorithm/string.hpp>
std::vector<std::string> strs;
boost::split(strs, "string to split", boost::is_any_of("\t "));

edited Dec 30, 2011 at 19:58

answered Dec 30, 2011 at 19:53

alex tingle

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5 Comments

Qiang Xu Over a year ago

Thanks, but I intend to discard the use of stream if possible.

Qiang Xu Over a year ago

Thank you, alex. Yeah, this is what I want. But I am not sure whether my g++ compiler comes with boost library, how to check the existence of boost? Btw, any additional -l command to use in compiling the source code? If there is no boost available, is there a similar utility function in STL?

alex tingle Over a year ago

Sorry for the ninja edit there. I mistook your question, at first.

Qiang Xu Over a year ago

By the way, alex. Just find another split()'s implementation in the classical "Accelerated C++" by Andrew Koenig. The implementation is provided in Section 5.6 (Taking strings apart) of Chapter 5.

ildjarn Over a year ago

@Qiang : You tagged your own question stream but you're trying to avoid streams? That's slightly misleading.

Sudeep · Accepted Answer · 2012-10-21 17:59:07Z

3

Code in c++
#include<sstream>
#include<vector>
using namespace std;    
string diskNames="vbbc anmnsa mansdmns";
string temp;
vector <string> cds;
stringstream s (diskNames);
while(s>> temp)
cds.push_back(temp);

answered Oct 21, 2012 at 17:59

Sudeep

531 silver badge9 bronze badges

Comments

Loki Astari · Accepted Answer · 2011-12-30 20:40:40Z

2

Use stream iterators and a standard function:

static int myfunc(std::string const& stringInput)
{
    std::stringstream ss(stringInput);

    std::for_each(std::istream_iterator<std::string>(ss),
                  std::istream_iterator<std::string>(),
                  [&counters](std::string const& word) { ++counters[word];}
                 )
    ...
}

If you don't have lambda then:

struct Helper
{
     void operator()(std::string const& word) const {++counters[word];}
     Helper(CounterType& c) : counters(c) {}
     CounterType& counters;
};

static int myfunc(std::string const& stringInput)
{
    std::stringstream ss(stringInput);

    std::for_each(std::istream_iterator<std::string>(ss),
                  std::istream_iterator<std::string>(),
                  Helper(counters)
                 )
    ...
}

edited Dec 30, 2011 at 20:40

answered Dec 30, 2011 at 20:33

Loki Astari

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1 Comment

Qiang Xu Over a year ago

Thank you, Loki. Your code looks awesome. Still, I prefer a way not to involve stream. :-)

Aaron McDaid · Accepted Answer · 2011-12-30 19:38:40Z

0

Use ostringstream, maybe

istringstream(stringInput); // initialize with the string

answered Dec 30, 2011 at 19:38

Aaron McDaid

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1 Comment

Qiang Xu Over a year ago

Yep, this saves a little bit. But the basic idea is still the same: construct a stringstream, and read from this stream. Could we not use the streamstream at all? And still read the space separated string into word?

Peter · Accepted Answer · 2011-12-30 21:04:38Z

0

In Visual C++ 11 you can use regex_token_iterator from TR1.

sregex_token_iterator::regex_type white_space_separators("[[:space:]]+",regex_constants::optimize);

for(sregex_token_iterator i(s.begin(),s.()end,white_space_separators,-1),end; i!=end; i++)
{
 cout << *i << endl;
 // or use i.start, i.end which is faster access
}

If you concerned about performance (and overheads like string copying), you can write your own routine:

#include <ctype.h>

#include <string>
#include <iostream>
using namespace std;

int main()
{
 string s = "Text for tokenization  ";

 const char *start = s.c_str();
 const char *end = start + s.size();
 const char *token = start;

 while (start!=end)
 {
   if(isspace(*start))
   {
    if (token < start)
    {
      // Instead of constructing string, you can 
      // just use [token,start] part of the input buffer
      cout << string(token,start) << ' ';
    }

    start++;
    token = start;
   }
   else
   {
    start++;
   }
 } 

 if (token < start)
 {
    cout << string(token,start) << ' ';
 }

}

edited Dec 30, 2011 at 21:04

answered Dec 30, 2011 at 20:48

Peter

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1 Comment

Qiang Xu Over a year ago

Thank you, Petro. Your split routine is quite similar to Andrew Koenig's in his "Accelerated C++". Both are nice functions.

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