Parsing a comma-delimited std::string

Question

If I have a std::string containing a comma-separated list of numbers, what's the simplest way to parse out the numbers and put them in an integer array?

I don't want to generalise this out into parsing anything else. Just a simple string of comma separated integer numbers such as "1,1,1,1,2,1,1,1,0".

Answer 1

void ExplodeString( const std::string& string, const char separator, std::list<int>& result ) {
    if( string.size() ) {
        std::string::const_iterator last = string.begin();
        for( std::string::const_iterator i=string.begin(); i!=string.end(); ++i ) {
            if( *i == separator ) {
                const std::string str(last,i);
                int id = atoi(str.c_str());
                result.push_back(id);
                last = i;
                ++ last;
            }
        }
        if( last != string.end() ) result.push_back( atoi(&*last) );
    }
}

Answer 2

std::string input="1,1,1,1,2,1,1,1,0";
std::vector<long> output;
for(std::string::size_type p0=0,p1=input.find(',');
        p1!=std::string::npos || p0!=std::string::npos;
        (p0=(p1==std::string::npos)?p1:++p1),p1=input.find(',',p0) )
    output.push_back( strtol(input.c_str()+p0,NULL,0) );

It would be a good idea to check for conversion errors in strtol(), of course. Maybe the code may benefit from some other error checks as well.

Answer 3

std::string str = "1,2,3,4,5,6";
std::vector<int> vect;

std::stringstream ss(str);

int i;

while (ss >> i)
{
 vect.push_back(i);

 if (ss.peek() == ',')
  ss.ignore();
}

Answer 4

#include <sstream>
#include <vector>

const char *input = "1,1,1,1,2,1,1,1,0";

int main() {
    std::stringstream ss(input);
    std::vector<int> output;
    int i;
    while (ss >> i) {
        output.push_back(i);
        ss.ignore(1);
    }
}

Bad input (for instance consecutive separators) will mess this up, but you did say simple.

Answer 5

Alternative solution using generic algorithms and Boost.Tokenizer:

struct ToInt
{
    int operator()(string const &str) { return atoi(str.c_str()); }
};

string values = "1,2,3,4,5,9,8,7,6";

vector<int> ints;
tokenizer<> tok(values);

transform(tok.begin(), tok.end(), back_inserter(ints), ToInt());

Answer 6

bool GetList (const std::string& src, std::vector<int>& res)
  {
    using boost::lexical_cast;
    using boost::bad_lexical_cast;
    bool success = true;
    typedef boost::tokenizer<boost::char_separator<char> > tokenizer;
    boost::char_separator<char> sepa(",");
    tokenizer tokens(src, sepa);
    for (tokenizer::iterator tok_iter = tokens.begin(); 
         tok_iter != tokens.end(); ++tok_iter) {
      try {
        res.push_back(lexical_cast<int>(*tok_iter));
      }
      catch (bad_lexical_cast &) {
        success = false;
      }
    }
    return success;
  }

Answer 7

Yet another, rather different, approach: use a special locale that treats commas as white space:

#include <locale>
#include <vector>

struct csv_reader: std::ctype<char> {
    csv_reader(): std::ctype<char>(get_table()) {}
    static std::ctype_base::mask const* get_table() {
        static std::vector<std::ctype_base::mask> rc(table_size, std::ctype_base::mask());

        rc[','] = std::ctype_base::space;
     rc['\n'] = std::ctype_base::space;
        return &rc[0];
    }
};

To use this, you imbue() a stream with a locale that includes this facet. Once you've done that, you can read numbers as if the commas weren't there at all. Just for example, we'll read comma-delimited numbers from input, and write then out one-per line on standard output:

#include <algorithm>
#include <iterator>
#include <iostream>

int main() {
    std::cin.imbue(std::locale(std::locale(), new csv_reader()));
    std::copy(std::istream_iterator<int>(std::cin), 
              std::istream_iterator<int>(),
              std::ostream_iterator<int>(std::cout, "\n"));
    return 0;
}

Answer 8

The String Toolkit Library (Strtk) has the following solution to your problem:

#include <string>
#include <deque>
#include <vector>
#include "strtk.hpp"
int main()
{ 
   std::string int_string = "1,2,3,4,5,6,7,8,9,10,11,12,13,14,15";
   std::vector<int> int_list;
   strtk::parse(int_string,",",int_list);

   std::string double_string = "123.456|789.012|345.678|901.234|567.890";
   std::deque<double> double_list;
   strtk::parse(double_string,"|",double_list);

   return 0;
}

More examples can be found Here