extern Storage Class in C

'extern' storage class

• In C, the extern storage class is used to declare variables or functions that are defined in another file and are accessible to multiple files.

• The extern keyword tells the compiler that the variable or function is defined elsewhere and should not allocate storage for it.

• Here's the syntax for declaring an extern variable:

extern data_type variable_name;

• Here's the syntax for declaring an extern function:

extern return_type function_name (parameters);

Example 1

Here's an example of using the extern storage class in C:

File main.c:

#include <stdio.h>

extern int x;

int main() {
   x = 10;
   printf("In main: x = %d\n", x);
   return 0;
}

File support.c:

#include <stdio.h>

int x;

void modify() {
   x = 20;
}

Explanation

The variable x is declared as extern in main.c and defined in support.c. The main.c file is able to access the value of x because of the extern declaration.

When the program is compiled and executed, the output will be:

In main: x = 10

This demonstrates how the extern storage class can be used to make a variable defined in one file accessible to other files in a program.