format a std::string with printf-style formatting

format_string.h

// utility function to do printf-style formatting on a std::string

#include <string>

template<typename ... Args>
static std::string format_string(const char* format, Args... args)
{
	if (format) {
		// get size from test run
		const size_t sz = std::snprintf(nullptr, 0, format, args ...);
		if(sz <= 0){
			return {};
		}

		// make a buffer
		std::vector<char> buf(sz + 1); // allow +1 for null terminator

		// write to buffer, and construct std::string retval from it
		std::snprintf(buf.data(), sz + 1, format, args...);
		return std::string(buf.data(), sz);
	}

	return {};
}