Integer to hex string in C++

Question

How do I convert an integer to a hex string in C++?

I can find some ways to do it, but they mostly seem targeted towards C. It doesn't seem there's a native way to do it in C++. It is a pretty simple problem though; I've got an int which I'd like to convert to a hex string for later printing.

Answer 1

Use <iomanip>'s std::hex. If you print, just send it to std::cout, if not, then use std::stringstream

std::stringstream stream; stream << std::hex << your_int; std::string result( stream.str() ); 

You can prepend the first << with << "0x" or whatever you like if you wish.

Other manips of interest are std::oct (octal) and std::dec (back to decimal).

One problem you may encounter is the fact that this produces the exact amount of digits needed to represent it. You may use setfill and setw this to circumvent the problem:

stream << std::setfill ('0') << std::setw(sizeof(your_type)*2)         << std::hex << your_int; 

So finally, I'd suggest such a function:

template< typename T > std::string int_to_hex( T i ) {   std::stringstream stream;   stream << "0x"           << std::setfill ('0') << std::setw(sizeof(T)*2)           << std::hex << i;   return stream.str(); } 

Answer 2

To make it lighter and faster I suggest to use direct filling of a string.

template <typename I> std::string n2hexstr(I w, size_t hex_len = sizeof(I)<<1) {     static const char* digits = "0123456789ABCDEF";     std::string rc(hex_len,'0');     for (size_t i=0, j=(hex_len-1)*4 ; i<hex_len; ++i,j-=4)         rc[i] = digits[(w>>j) & 0x0f];     return rc; }