Differences Between The Internal And External Static Variables In C

Static variables are a category of variables that maintain their value across multiple function calls. Unlike regular variables, which are initialized and destroyed with each function call, static variables persist throughout the entire runtime of the program. The "static" keyword is used to declare static variables.

There exist two categories of static variables: Internal and External static variables.

Internal static variables:

Static variables declared within a function are defined using the static keyword. These variables are confined to the function's scope in which they are declared and cannot be accessed or altered directly from outside the function. They are commonly referred to as local variables.

Example:

Let's consider a C program to demonstrate the usage of internal static variables:

Example


#include <stdio.h>

void magicRoom() {

 static int magicBox = 5;

 printf("Magic Box in the room: %d\n", magicBox);

 magicBox++;

}

int main() {

 magicRoom();

 magicRoom();

 magicRoom();

 return 0;

}

Output:

Output


Magic Box in the room: [value]

Explanation:

In this instance, the program contains two functions: magicRoom and the primary function. Within the magicRoom function, there is an internal static variable called magicBox that is set to an initial value of 5.

It displays the value stored in magicBox and increases it each time the magicRoom function is invoked thrice within the main function.

Internal static variables are confined within the scope of the magicRoom function, ensuring encapsulation and preventing direct access from external sources. Initially set to 5, the magicBox value increments upon the first function call. Subsequently, each function call results in printing the updated magicBox value along with an increment.

External static variables:

Global static variables in C are declared with the static keyword at the global scope. They can be accessed from any part of the program, not limited to specific functions. These variables maintain their values throughout the entire program runtime.

Example:

Let's consider a C program to demonstrate the usage of external static variables:

Example


#include <stdio.h>

static int globalMagicNumber = 10;

void mathClass() {

 printf("Global Magic Number in Math class: %d\n", globalMagicNumber);

}

void scienceClass() {

 printf("Global Magic Number in Science class: %d\n", globalMagicNumber);

}

int main() {

 printf("Global Magic Number in the main program: %d\n", globalMagicNumber);

 mathClass();

 scienceClass();

 return 0;

}

Output:

Output


Magic Box in the room: [value]

Explanation:

In this scenario, the significance of external static variables is demonstrated. Within the program, there exist three functions: mathClass, scienceClass, and main. At the beginning of the program, an external static variable, globalMagicNumber, is defined and set to 10. This variable is globally accessible within the program, hence it is utilized in the mathClass, scienceClass, and main functions. The value assigned to globalMagicNumber remains consistent throughout the entire program execution.