How to pass variable number of arguments to printf/sprintf

Use vfprintf, like so:

void Error(const char* format, ...)
{
    va_list argptr;
    va_start(argptr, format);
    vfprintf(stderr, format, argptr);
    va_end(argptr);
}

This outputs the results to stderr. If you want to save the output in a string instead of displaying it use vsnprintf. (Avoid using vsprintf: it is susceptible to buffer overflows as it doesn’t know the size of the output buffer.)