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wrapper printf function that filters according to user preferences

Asked 2009-10-04T13:07:08.493
30

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). 

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

The preferences is handled by some flags:

unsigned short PRIO_LOG = (PRIO_HIGH | PRIO_NORMAL);
unsigned short PRIO_STD = (PRIO_HIGH);

The write_log function should work with the same parameters as the printf function, with the added parameter of unsigned short priority.

write_log((PRIO_NORMAL|PRIO_LOW), "HELLO %s, take %d", "World", 1);

(Even if PRIO_NORMAL|PRIO_LOW makes little sense...)

Checking the flags is easy: if(priority & PRIO_LOG) (Returns >1 if any flag is set in both arguments)

I cannot however find out how I would go about passing the string literal and the format arguments to the printf function. Can anyone help or give me a pointer (possible to an alternative method that achieves the same effect)? It would be much appreciated.

c filter printf wrapper
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1 Answer

11

I think Jeff's idea is the way to go, but you can also accomplish this with a macro without using vprintf. This might require gcc:

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

Check here for info about how this works.

answered 2009-10-04T18:42:15.990

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