CODEWITHSUNDEEP
cmacrosc-preprocessor
Venkat Krishnan
Venkat Krishnan

Reputation: 117

C Macro expansion into multiple function definitions

I have 3 very similar log functions that will be called from different places.

void INFO (char *format, ...) {
   char log_buf[256] = {0};
   va_list args;
   va_start(args, format);
   vsprintf(log_buf, format, args);
   va_end(args);
   LIB_LOG_INFO(log_buf);
}

void ERROR (char *format, ...) {
   char log_buf[256] = {0};
   va_list args;
   va_start(args, format);
   vsprintf(log_buf, format, args);
   va_end(args);
   LIB_LOG_ERROR(log_buf);
}

void DEBUG (char *format, ...) {
   char log_buf[256] = {0};
   va_list args;
   va_start(args, format);
   vsprintf(log_buf, format, args);
   va_end(args);
   LIB_LOG_DEBUG(log_buf);
}

I cannot pass any extra arguments, so I cannot do an if-else to call the different LIB_LOG functions.

Is it possible to write a generic macro that will expand into these 3 function definitions at compile time? Only the names of the LIB_LOG functions are different.

Upvotes: 0

Views: 1318

Answers (1)

Lundin
Lundin

Reputation: 213678

First of all please note that variable argument functions in particular are almost certainly the wrong solution to any problem. They are to be regarded as a deprecated, dangerous feature - avoid them if possible.

The being said, you can solve your problem by making a single generic function that takes a function pointer parameter:

typedef void lib_log_func_t (char* buf);

void lib_log (lib_log_func_t* func, const char* format, ...)
{
  char log_buf[256] = {0};
  va_list args;
  vsprintf(log_buf, format, args);
  va_end(args);
  func(log_buf);
}

Then write 3 wrapper macros:

#define INFO(format, ...)  lib_log(LIB_LOG_INFO,  format, __VA_ARGS__)
#define ERROR(format, ...) lib_log(LIB_LOG_ERROR, format, __VA_ARGS__)
#define DEBUG(format, ...) lib_log(LIB_LOG_DEBUG, format, __VA_ARGS__)

Upvotes: 2

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