Convenient C's printf in C++

vprintf.cpp

// this is a buffer-overflow-safe version of sprintf
// source: http://stackoverflow.com/a/69911
// if you need something more mature, consider https://github.com/fmtlib/fmt
// the advantage of this snippet is that it can be really easily added to smallish
// codes/libraries. Usage is like C's vprintf et al. but with a C++ std::string as a result.
std::string vformat (const char *fmt, va_list ap) {
    // Allocate a buffer on the stack that's big enough for us almost
    // all the time.  Be prepared to allocate dynamically if it doesn't fit.
    size_t size = 1024;
    char stackbuf[1024];
    std::vector<char> dynamicbuf;
    char *buf = &stackbuf[0];
    va_list ap_copy;

    while (1) {
        // Try to vsnprintf into our buffer.
        va_copy(ap_copy, ap);
        int needed = vsnprintf (buf, size, fmt, ap);
        va_end(ap_copy);

        // NB. C99 (which modern Linux and OS X follow) says vsnprintf
        // failure returns the length it would have needed.  But older
        // glibc and current Windows return -1 for failure, i.e., not
        // telling us how much was needed.

        if (needed <= (int)size && needed >= 0) {
            // It fit fine so we're done.
            return std::string (buf, (size_t) needed);
        }

        // vsnprintf reported that it wanted to write more characters
        // than we allotted.  So try again using a dynamic buffer.  This
        // doesn't happen very often if we chose our initial size well.
        size = (needed > 0) ? (needed+1) : (size*2);
        dynamicbuf.resize (size);
        buf = &dynamicbuf[0];
    }
}

std::string sformat(const char *fmt, ...) {
	va_list ap;
	va_start (ap, fmt);
	std::string buf = vformat (fmt, ap);
	va_end (ap);
	return buf;
}