Converting a float to std::string in C++

Question

This is a seemingly simple problem, but I'm having difficulty coming up with an answer. I have a float value that needs to be put into a std::string, like so:

float val = 2.5;
std::string my_val = val; // error here

Obviously they're of different types. How do I convert from float to string?

All help is appreciated.

Answer 1

Unless you're worried about performance, use string streams:

std::ostringstream ss;
ss << myFloat;
std::string s(ss.str());

If you're okay with Boost, lexical_cast<> is a convenient alternative:

std::string s = boost::lexical_cast<std::string>(myFloat);

Efficient alternatives are e.g. FastFormat or simply the C-style functions.

Answer 2

Check the must-read C++ FAQ by Marshall Cline and the question:

• How do I convert a value (a number, for example) to a std::string?

Answer 3

If you're worried about performance, check out the Boost::lexical_cast library.

Answer 4

You can define a template which will work not only just with doubles, but with other types as well.

template <typename T> string tostr(const T& t) { ostringstream os; os<<t; return os.str(); } 

Then you can use it for other types.

double x = 14.4;
int y = 21;

string sx = tostr(x);
string sy = tostr(y);