StringFromFormat

#include <cstdio>
#include <cstdarg>
#include <iostream>
#include <string>

#ifdef __GNUC__
#   if defined _WIN32 && !defined __USE_MINGW_ANSI_STDIO
__attribute__((__format__ (ms_printf, 1, 2)))
#   else
__attribute__((__format__ (printf, 1, 2)))
#   endif
#endif
std::string StringFromFormat(const char *format, ...)
{
    std::va_list args;
    va_start(args, format);
    std::size_t num = static_cast<std::size_t>(vsnprintf(NULL, 0, format, args));
    std::string result(num, '\0');
    vsprintf(&result[0], format, args);
    va_end(args);
    return result;
}

int main()
{
    using namespace std;
    cout << StringFromFormat("%d+%d=%d23423423423423sdfgsdfgsdfgsdfg42342342343434234", 1, 2, 3);
}