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:

#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:

#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 the current date in   
                        "MMM DD YYYY" format.

2 _TIME_ represents current time in                                        "HH:MM: SS" format.

3 _FILE_ represents the current file name.

4 _LINE_ represents current line number.

5 _STDC_ It is defined as 1 when
                         compiler compiles 
                        with the ANSI standard.

C predefined macros example

File: simple.c

#include<stdio.h>  
 int main(){    
   printf("File :%s\n", __FILE__ );    
   printf("Date :%s\n", __DATE__ );    
   printf("Time :%s\n", __TIME__ );    
   printf("Line :%d\n", __LINE__ );    
   printf("STDC :%d\n", __STDC__ );      
   return 0;  
 }    
Output:

File :simple.c
Date :Dec 6 2015
Time :12:28:46
Line :6
STDC :1