Duanxx C + + Learning: Debugging code with __FILE__,__LINE__,__VA_ARGS__

__file__,__line__

When we debug C + + code, what we want to know is, of course, the first line of the file that the program is currently on, and there are two macros: __file__ and __line__, which returns the path to the current file, and the current line.

Here the test code is as follows:

#include <cstdio>int main () {  printf ("%s:%d", __file__,__line__);  printf ("\ n");  return 0;}

The results under Windows Run as:

The results of the Linux system operation are as follows:

As you can see, under Windows, __FILE__ returns the Full path , and with g++ compiled under Linux, the return is only file name .

__va_args__

This is a variable parameter macro that was supported from C99, which previously supported only variable parameters of a function in the C language.

For example, our most common printf function:

void printf (const char* format, ...);

Here's the ellipsis ..., yes . variable Parameters .

The __VA_ARGS__ macro is the variable parameter that implements the macro:

#define DEBUG (...) printf (__va_args__)

The test code is as follows:

#include <cstdio> #define DEBUG (...) printf (__va_args__) int main () {  debug ("Duanxx%d\n", 123);  return 0;}

Running results under Windows:

Running results under Linux:

A single line of debug macros

With the instructions above, you can write the following debug macro:

#define DEBUG (FMT, ...)   fprintf (stdout, "%s:%d duanxx Debug   " FMT "\ n", __file__, __line__, # #__VA_ARGS__)

Test code:

#include <cstdio> #define DEBUG (FMT, ...)   fprintf (stdout, "%s:%d duanxx debug   " FMT "\ n", __file__, __line__, # #__VA_ARGS__) int main () {  debug ("Duanxx%d\n ", 123);  return 0;}

Results under Windows:

Results under Linux:

Duanxx C + + Learning: Debugging code with __FILE__,__LINE__,__VA_ARGS__