A storage class identifies the visibility of variables or functions in a C program. There are 4 different storage classes in a C language.
static
register
auto
extern
Register Storage Class
The register storage class is to define local variables and should be stored in a register instead of RAM. Here is an example syntax of the register storage class.
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{ register int rollNo; } |
Static Storage Class
Static storage class tells the compiler to keep local variables for a lifetime. Making local variables static allows them to maintain their values when function call. Here is a C program for static storage class.
Program:
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#include <stdio.h>
/* Declare a function */ void func(void);
static int count = 10; /* global variable */
main() {
while(count--) { func(); }
return 0; }
/* Define a function */ void func( void ) {
static int i = 5; /* Create local static variable */ i++;
printf("i is %d and count is %d\n", i, count); } |
Output:
i is 12 and count is 3
i is 13 and count is 2
i is 14 and count is 1
i is 15 and count is 0
Extern Storage Class
The external storage is generally used to give a reference to the global variables. It is visible for all the program files and cannot be initialized. Also, points the variable name at a storage location. Let's have a look at the short example of extern storage.
Program:
1rst File main.c
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#include <stdio.h>
int count ; extern void w_e();
main() { count = 5; w_e(); } |
2nd File second.c
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#include <stdio.h>
extern int count;
void w_e(void) { printf("Count is %d\n", count); } |
Extern storage class is used to declare count in second.c file.
Output:
count is 5