How do I convert a double into a string in C++?

Question

// The C way:
char buffer[32];
snprintf(buffer, sizeof(buffer), "%g", myDoubleVar);

// The C++03 way:
std::ostringstream sstream;
sstream << myDoubleVar;
std::string varAsString = sstream.str();

// The C++11 way:
std::string varAsString = std::to_string(myDoubleVar);

// The boost way:
std::string varAsString = boost::lexical_cast<std::string>(myDoubleVar);

The boost (tm) way:

std::string str = boost::lexical_cast<std::string>(dbl);

The Standard C++ way:

std::ostringstream strs;
strs << dbl;
std::string str = strs.str();

Note: Don't forget #include <sstream>

The Standard C++11 way (if you don't care about the output format):

#include <string>

auto str = std::to_string(42.5); 

to_string is a new library function introduced in N1803 (r0), N1982 (r1) and N2408 (r2) "Simple Numeric Access". There are also the stod function to perform the reverse operation.

If you do want to have a different output format than "%f", use the snprintf or ostringstream methods as illustrated in other answers.

You can use std::to_string in C++11

double d = 3.0;
std::string str = std::to_string(d);

If you use C++, avoid sprintf. It's un-C++y and has several problems. Stringstreams are the method of choice, preferably encapsulated as in Boost.LexicalCast which can be done quite easily:

template <typename T>
std::string to_string(T const& value) {
    stringstream sstr;
    sstr << value;
    return sstr.str();
}

Usage:

string s = to_string(42.5);