Predefined Macros & other pre-processor directives

Recap - Preprocessor directive

Preprocessor is a king of automated editor that modifies a copy of the original source code
The #include directive causes the preprocessor to fetch the contents of some other file to be included in the present file
In C programming there are two common formats for #include:
This file may in turn #include some other file(s) which may in turn do the same
Most commonly #included files have a ".h" extension, indicating that they are header files.
The #define directive is used to "define" preprocessor "variables"

Other C Preprocessor

#undef

Undefines a macro or preprocessor variable

#ifdef

Returns true if some preprocessor variable or macro is defined

#ifndef

Returns true if some preprocessor variable or macro is not defined

#if

#else

elif

pragma

it is used to issue some special commands to the compiler

Predefined Macros in C

__DATE__→ The current date as character literal in "MMM DD YYY" format.
__TIME__→ This contains the current time as a character literal in "HH:MM:SS" format.
__FILE__→ The current filename as a string literal.
__LINE__→ The current line number as a decimal constant.
__STDC__→ Defined as 1(one) when the compiler complies with the ANSI standard.

FILE

#include <stdio.h>
int main()
{
printf("File name is %s\n",__FILE__);
return 0;
}

The file name is code.c

DATE

#include <stdio.h>
int main()
{
printf("Today's date is %s\n",__DATE__);
return 0;
}

Today's date is Jul 10 2022

TIME

#include <stdio.h>
int main()
{
printf("Time now is %s\n",__TIME__);
return 0;
}

Time now is 10:49:55

LINE

#include <stdio.h>
int main()
{
printf("Line no is %d\n",__LINE__);
return 0;
}

Line no is 4

STDC

#include <stdio.h>
int main()
{
printf("ANSI: %d\n",__STDC__);
return 0;
}

ANSI: 1

C Programming