Best way to cast numbers into strings in C++?

Question

Coming from a C# background, In C# I could write this:

int int1       = 0;
double double1 = 0;
float float1   = 0;

string str = "words" + int1 + double1 + float1;

..and the casting to strings is implicit. In C++ I understand the casting has to be explicit, and I was wondering how the problem was usually tackled by a C++ programmer?

There's plenty of info on the net already I know, but there seems to quite a number of ways to do it and I was wondering if there wasn't a standard practice in place?

If you were to write that above code in C++, how would you do it?

Lightness Races in Orbit · Accepted Answer · 2014-01-09T19:30:06.690

Strings in C++ are just containers of bytes, really, so we must rely on additional functionality to do this for us.

In the olden days of C++03, we'd typically use I/O streams' built-in lexical conversion facility (via formatted input):

int    int1    = 0;
double double1 = 0;
float  float1  = 0;

std::stringstream ss;
ss << "words" << int1 << double1 << float1;

std::string str = ss.str();

You can use various I/O manipulators to fine-tune the result, much as you would in a sprintf format string (which is still valid, and still seen in some C++ code).

There are other ways, that convert each argument on its own then rely on concatenating all the resulting strings. boost::lexical_cast provides this, as does C++11's to_string:

int    int1    = 0;
double double1 = 0;
float  float1  = 0;

std::string str = "words"
   + std::to_string(int1) 
   + std::to_string(double1) 
   + std::to_string(float1);

This latter approach doesn't give you any control over how the data is represented, though (demo).

Shouldn't we be closing this as an exact dupe rather than...? — legends2k, Jan 09 '14 at 19:29

score 4 · Answer 2 · answered Jan 09 '14 at 19:26

If you can use Boost.LexicalCast (available for C++98 even), then it's pretty straightforward:

#include <boost/lexical_cast.hpp>
#include <iostream>

int main( int argc, char * argv[] )
{
    int int1       = 0;
    double double1 = 0;
    float float1   = 0;

    std::string str = "words" 
               + boost::lexical_cast<std::string>(int1) 
               + boost::lexical_cast<std::string>(double1) 
               + boost::lexical_cast<std::string>(float1)
    ;

    std::cout << str;
}

Live Example.

Note that as of C++11, you can also use std::to_string as mentioned by @LigthnessRacesinOrbit.

score 2 · Answer 3 · answered Jan 09 '14 at 19:27

Being a C developer, I would use the C string functions, as they are perfectly valid in C++, and let you be VERY explicit with respect to the formatting of numbers (ie: integers, floating point, etc).

http://www.cplusplus.com/reference/cstdio/printf/

In the case of this, sprintf() or snprintf() is what you are looking for. The formats specifiers make it very obvious in the source code itself what your intent was as well.

XOR · Answer 4 · 2019-11-06T16:07:19.307

The best way to cast numbers into std::string in C++ is to use what is already available. The library sstream provide a stream implementation for std::string. It is like using a stream ( cout, cin ) for example

Its easy to use : http://www.cplusplus.com/reference/sstream/stringstream/?kw=stringstream

#include <sstream>
using std::stringstream;
#include <string>
using std::string;
#include <iostream>
using std::cout;
using std::endl;

int main(){
   stringstream ss;
   string str;
   int i = 10;

   ss << i;
   ss >> str;

   cout << str << endl;     
}

Best way to cast numbers into strings in C++?

4 Answers4