C Programming Tutorial
The #include preprocessor directive is used to paste code of given file into current file. It is used include system-defined and user-defined header files. If included file is not found, compiler renders error.
By the use of #include directive, we provide information to the preprocessor where to look for the header files. There are two variants to use #include directive.
- #include
- #include "filename
The #include
The #include "filename" tells the compiler to look in the current directory from where program is running.
#include directive example
Let's see a simple example of #include directive. In this program, we are including stdio.h file because printf() function is defined in this file.
#include<stdio.h>
int main(){
printf("Hello C");
return 0;
}
Output:
Hello C
#include notes:
Note 1: In #include directive, comments are not recognized. So in case of #include <a//b>, a//b is treated as filename.
Note 2: In #include directive, backslash is considered as normal text not escape sequence. So in case of #include #include <a\nb>, a\nb is treated as filename.
Note 3: You can use only comment after filename otherwise it will give error.
Example
Let's look at an example of how to use #include directives in your C program.
In the following example, we are using the #include directive to include the stdio.h header file which is required to use the printf standard C library function in your application.
/* Example using #include directive by C programming */
#include <stdio.h>
int main()
{
/*
* Output "c programming began in 2018" using the C standard library printf function
* defined in the stdio.h header file
*/
printf("c programming began in %d\n", 2018);
return 0;
}
In this example, the program will output the following:
c programming began in 2018
Header Files
This is a list of the header files that you can include in your program if you want to use the functions available in the C standard library:
| Header File | Type of Functions |
|---|---|
| <assert.h> | Diagnostics Functions |
| <ctype.h> | Character Handling Functions |
| <locale.h> | Localization Functions |
| <math.h> | Mathematics Functions |
| <setjmp.h> | Nonlocal Jump Functions |
| <signal.h> | Signal Handling Functions |
| <stdarg.h> | Variable Argument List Functions |
| <stdio.h> | Input/Output Functions |
| <stdlib.h> | General Utility Functions |
| <string.h> | String Functions |
| <time.h> | Date and Time Functions |
