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C Macros

A macro is a segment of code which is replaced by the value of macro. Macro is defined by #define directive. There are two types of macros:

  1. Object-like Macros
  2. Function-like Macros

Object-like Macros

The object-like macro is an identifier that is replaced by value. It is widely used to represent numeric constants. For example:

  1. #define PI 3.14

Here, PI is the macro name which will be replaced by the value 3.14.

Function-like Macros

The function-like macro looks like function call. For example:

  1. #define MIN(a,b) ((a)<(b)?(a):(b))  

Here, MIN is the macro name.

Visit #define to see the full example of object-like and function-like macros.

C Predefined Macros

ANSI C defines many predefined macros that can be used in c program.

No. Macro Description
1 _DATE_ represents current date in “MMM DD YYYY” format.
2 _TIME_ represents current time in “HH:MM:SS” format.
3 _FILE_ represents current file name.
4 _LINE_ represents current line number.
5 _STDC_ It is defined as 1 when compiler complies with the ANSI standard.

C predefined macros example

File: simple.c

  1. #include <stdio.h>
  2. main() {
  3.    printf(“File :%s\n”, __FILE__ );
  4.    printf(“Date :%s\n”, __DATE__ );
  5.    printf(“Time :%s\n”, __TIME__ );
  6.    printf(“Line :%d\n”, __LINE__ );
  7.    printf(“STDC :%d\n”, __STDC__ );
  8. }


File :simple.c
Date :Dec 6 2015
Time :12:28:46
Line :6