wrapper printf function that filters according to user preferences

Question

My program writes to a log and to stdout. Every message, however, has a certain priority and the user specifies in Preferences which priorities go to which stream (log or stdout

Answer 1

You want to call vprintf() instead of printf() using the variable arguments "varargs" capabilities of C.

#include 

int write_log(int priority, const char *format, ...)
{
    va_list args;
    va_start(args, format);

    if(priority & PRIO_LOG)
            vprintf(format, args);

    va_end(args);
}

For more information, see something along the lines of this.