std::string formatting like sprintf

Question

I have to format std::string with sprintf and send it into file stream. How can I do this?

Answer 1

I realize this has been answered many times, but this is more concise:

std::string format(const std::string fmt_str, ...)
{
    va_list ap;
    char *fp = NULL;
    va_start(ap, fmt_str);
    vasprintf(&fp, fmt_str.c_str(), ap);
    va_end(ap);
    std::unique_ptr formatted(fp);
    return std::string(formatted.get());
}

example:

#include 
#include 

int main()
{
    std::random_device r;
    std::cout << format("Hello %d!\n", r());
}

See also http://rextester.com/NJB14150