C Macro question

[ddm at pizzashack.org (Derek D. Martin)]

At some point hitherto, Frank Ramsay hath spake thusly:
> I'm horrible with Macros in C does anyone know how to make a macro
> that w

?

> Now I have a ton of these so altering them manually would take much
> longer than I have.  Does anyone know of a macro or function that
> takes var args for printf and re-formats them to a more logfile
> friendly format?

Well, I'm not exactly sure what you're looking for, but I've written
functions and macros that do something that sounds similar.  They take
a format string, followed by variable arguments, and use them to
create a message to send to syslog().

The function that does the logging is declared as such:

  /* log a standard log message with the given priority */
  void      log_msg( int priority, char *msg, ... );

Then I have two macros that use this function, defined like this:

  #define   error_msg( format, args... ) log_msg( LOG_ERR, format, ##args )
  #define   debug_msg( format, args... ) log_msg( LOG_DEBUG, format, ##args )

The log_msg() function uses vnsprintf() to stick all the args in a
suitable buffer, ? la:

     /* stuff for variable arg list */
     va_start( arg_item, msg );
     vsnprintf( buff, ( length + MAX_MSG_LEN ), msg, arg_item );

     va_end( arg_item );

If that's not what you're looking for, it should at least illustrate
how to do what you're trying to do. 

FYI, this (the macro stuff, that is) is documented in an obscure part
of the Gnu C preprocessor documentation.  It may be a Gnu-specific
extension...  I haven't been able to find any other place (i.e. text
books) where this feature is described.

-- 
Derek Martin               ddm at pizzashack.org    
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