Macros in C Program

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:

Object-like Macros 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.

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: micro-test.c

#include <stdio.h>  
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__ );  
}  

Output:

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