Variable-parameter macros

Reference from:

Http://www.cnblogs.com/lixiaohui-ambition/archive/2012/08/21/2649052.html

http://blog.csdn.net/aobai219/article/details/6092292

Http://www.cnblogs.com/MarvinGeng/archive/2012/07/19/2598923.html

Thank Lizezheng, Tonggetongge, Marvingeng Guide!

Variable-parameter macros:

1. Variable-parameter macros are supported by the C99 specification, as follows:

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

The default number represents a table of parameters that can be changed. Use the reserved name __va_args__ to pass parameters to the macro. When the macro's call is expanded, the actual parameters are passed to printf () .

If the default number is preceded by a comma, it is written in the following form:

#define DEBUG (format, ...) printf (format, # #__VA_ARGS__)

' # # ' means that if the variable parameter is ignored or empty, the preprocessor (preprocessor) is removed from the comma in front of it.

2. Compiler built-in macro definition:

Standard scheduled macros for ANSI C:

__date__: Replace with the current date in the format of "Month Day Year", type string

__FILE__: Replace with current source file name includes path, type is string

__LINE__: Replaced with the current line number, can be set in conjunction with #line, #line之后的数字代表 the line number of the next line, followed by the line number, and so on, the type is an integer value.

__STDC__: This identity is assigned a value of 1 when a program is required to strictly adhere to the ANSI C standard

__TIME__: Replace with the current time in "time: minutes: Seconds" format, type string

__TIMESTAMP__: Replace with the format "Day of the Week: minute: Second year" as the last time the current source file was modified, type string

For a detailed description, see:

Https://msdn.microsoft.com/en-us/library/b0084kay (vs.80). aspx

3. A combination of the two can generate useful debug output macros, such as:

1 #define __debug__  2#ifdef __debug__  3#define DEBUG (format, ...) printf ("Line:%4d time     :" __time__ "    " format "\ n", __line__,# #__VA_ARGS__)  4#else  5#define DEBUG (format,...)  6 #endif

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Variable-parameter macros