String handling inside Preprocessor macro

Question

I need to change a implementation of Macro(LOGGING_MACRO) printf into syslog.

Macro Usage :

LOGGING_MACRO(5,("Value of x,y=%d,%d\n",x,y));

Def1 :

#define LOGGING_MACRO(loglevel,str) printf str;

Def2 :

#define LOGGING_MACRO(loglevel,str) syslog(loglevel,str);

Note : I cannot change the macro format :(

Def2 throws error as syslog will not accept 'str'(2nd arg) with front & back braces. [But working fine in Def1 with printf ]

Kindly suggest how to remove the 1st & last braces from 'str' inside the macro before passing 'str' to syslog.

Give an example how you call your macro, because this approach printf str; is completelly failed. — unalignedmemoryaccess
– unalignedmemoryaccess, Commented Apr 21, 2017 at 7:01
This is not possible what you are asking directly, but if you use local variable then it can be done. Edit: No, it can't. You failed your usage. — unalignedmemoryaccess
– unalignedmemoryaccess, Commented Apr 21, 2017 at 7:05
Any other ways i can edit content of 'str' inside a macro ??? — Balaganesh.V
– Balaganesh.V, Commented Apr 21, 2017 at 7:08

unalignedmemoryaccess · Accepted Answer · 2017-04-21 07:40:07Z

Example below will work in single thread application:

char* custom_log(const char *fmt, ...) { static char outputString[200]; //Adjust your size for maximal log value va_list args; va_start(args, fmt); vsprintf(outputString, fmt, args); va_end(args); return outputString; }

Then modify your macro to:

#define LOGGING_MACRO(loglevel,str) syslog(loglevel, custom_log str)

Remember, this works only in single-thread mode and make sure, custom_log function is visible where custom_log function is called.

For multi-thread, you might update it like this:

#define LOGGING_MACRO(loglevel,str) do {\ mutex_lock(); /*Lock your mutex for debug print*/ \ syslog(loglevel, custom_log str); /*Debug*/ \ mutex_unlock(); /*Unlock mutex*/ \ } while (0)

Keep in mind that you have to write mutex_lock and mutex_unlock functions for your requirements in your system to lock only debug functions between multi threads.

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