Variable parameter macros (DEBUG)

have been written around printf to print debugging information, do not need to be a comment out. After the Internet query found there are many ways to debug printing, parameters variable and convenient one-time switch.

#define DEBUG (FMT,...) printf (fmt,__va_args__) Here "..." refers to a mutable parameter.

int main () {DEBUG ("Hello%d", ten); return 0;}

Sometimes, a module has output information, error messages, and so on. If you want to open a section individually, you can design:

  1: #define DRV_DEBUG       1
  2: #define DRV_DEBUG_IN    0x0001
  3: #define Drv_debug_out   0x0002
  4: #define DRV_DEBUG_ERR   0x0004
  5: #define Drv_debug_all   0xFFFF
  6: #if drv_debug
  7:      unsignedint drv_flags = Drv_debug_err | Drv_debug_out;
  8:      #define DRV_PRINT (flag, FMT, ...)        
  9: Do        {                                  
:            if (drv_flags & Flag) {           
One:                 printf(FMT, __va_args__);}  
:            } while(0)
: #Else
: #define DRV_PRINT (FMT,...)
: #endif

In this way, I just print out and err:

  void drv_write (char * msg_out)
  2: {
  3:drv_print (Drv_debug_out, "%s", msg_out); //Output
  4:drv_print (Drv_debug_err, "%s", msg_out); //Output
  5:drv_print (drv_debug_in, "%s", msg_out); //No output
  6:}
Further, can be designed for the entire system of different modules of the log output control! TCP/IP protocol stack implementation LWIP that's how it's done.

But found that the light has printf is not enough, although debugging information is out, but in so many debugging information can not immediately know where this information is printed from. So you can use a different method to print the file name and source location.

There are several macros in ANSI C

__line__: Inserting the current line number

__file__: Inserting the current original file name

__date__: Inserting the current compilation date
__time__: Inserting the current compile time

So that's what the macro looks like. Debug (fmt,...)    printf ("FILE:" __file__ "", line:%d: "FMT" \ n ", __line__,# #__VA_ARGS__)

Pay special attention to the following # #__VA_ARGS__这里的 # #是很有必要的, because he means that if there are no arguments, let the preprocessor ignore the preceding comma. The first paragraph above does not add parameters to the error. So the first paragraph must have parameters.

Drv_print (drv_debug_out, "Hello World");//There is a problem, you need to change the macro definition, preceded by # #

Variable parameter macros (DEBUG)