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

If you want the PRIO_* definitions to be used as bit (using | and &), you must give each one of them its own bit:

unsigned short PRIO_HIGH = 0x0001;
unsigned short PRIO_NORMAL = 0x0002;
unsigned short PRIO_LOW = 0x0004;

The macro can be improved by using the do { } while (0) notation. It makes the calls to write_log act more like a statement.

#define write_log(priority,format,args...) do { \
    if (priority & PRIO_LOG) { \
        printf(format, ## args); \
    } while(0)