What is use of static function in C language programming?

Answer includes the use of static function in C programming with explanation and C code example.

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Answer:

For below reasons we should use static function in C program.

• Limit the scope/visibility of a function in a C programs.
• Reuse of the same function name in other C source files

Let’s explain both above uses with a program example in C.

MUST READ: Are static functions in C and C++ same?

1) Limit the scope/visibility of a function in a C program

In a C source file, generally, we have internal and public APIs and we make the visibility of public APIs only to client (e.g. main()). So, in C programming , we use static functions to restrict the access of internal APIs to client.

As an example, let’s have a music.h header file that contains declaration of two functions “static void buffer()” as an internal function for buffering music and PlayMusic() as a public functions . in music.c we will define these functions.

In the below C program, only PlayMusic() function will be accessible to main.c source file and buffer() function to file itself i.e. music.c only and not to main.c as it is a static function.

//music.h //header file

 
//music functions
static void buffer();
void playMusic();

//music.c //source file

    
#include "music.h" 

void buffer(){
printf("Buffering Music...\n");
}
void playMusic()  
{  
	buffer();
	printf("Play Music\n");  
}  

//Client – main.c

#include "music.h"
int main()
{
	//buffer();//compiler error :Not accessible here
	playMusic();	
	
	return 0;
}
  

Output:
Buffering Music…
Play Music

2) Re-use of the same function name in other source files

In C language programming , static function is also used to avoid ambiguity. If we have the same function name in different source files in an application.

For example, in above program lets include one more file “video.h” and “video.c” that have function with same name i.e. void buffer() as we have in music.h.

//Video.h – header file

//Video functions

static void buffer();

void playVideo();

//video.c – source file

#include "video.h"

void buffer(){

printf("Buffering Video...\n");

}

void playVideo()

{

buffer();

printf("Play Video\n");

}

In files music.h and video.h if the buffer() function is not static we’ll get compiler error in following program as compiler will find buffer in music.h first and then it goes to video.h and find the same and complain that buffer() is already defined in music.h.

#include "music.h"
#include "video.h"  
int main()
{
	//buffer();//compiler error :Not accessible here
	playMusic();	
	playVideo();
	return 0;
}

So, Once we make buffer() function as static no conflict will occur, hence function name can be reused in a same program.

Static function – Complete C Program Example:

//music.h

#include    

//music functions
static void buffer();
void playMusic();

//music.c

  
#include "music.h"  

void buffer(){
printf("Buffering Music...\n");
}
void playMusic()  
{  
	buffer();
	printf("Play Music\n");  
}  

//video.h

//Video functions
static void buffer();
void playVideo();

 
//video.c
 

#include "video.h"

void buffer(){
printf("Buffering Video...\n");
}
void playVideo()  
{  
	buffer();
	printf("Play Video\n");  
}  

#include "video.h"

void buffer(){
printf("Buffering Video...\n");
}
void playVideo()  
{  
	buffer();
	printf("Play Video\n");  
}  

//main.c

#include "music.h"
#include "video.h"  
int main()
{
	//buffer();//compiler error :Not accessible here
	playMusic();	
	playVideo();
	return 0;
}