Static variables

C

Reference manual

In C, static variables are used to preserve their values between function calls, making them retain their values across multiple invocations of the same function. They are defined using the static keyword and can be either local to a function or global.

Static variables are initialized to zero by default if no initial value is provided.

It’s essential to be aware of the scope and lifetime of static variables to avoid unintended side effects when using them.

Syntax

static data_type variable_name;

Local static variables

When a static variable is declared within a function, it is referred to as a local static variable. Local static variables are initialized only once, at the start of the program, and retain their values between function calls. They have block scope, meaning they are only accessible within the function where they are defined.

Global static variables

When a static variable is declared outside of any function or at the file scope, it is referred to as a global static variable. Global static variables are initialized only once at the start of the program, are available for the entire lifetime of the program and they are accessible from any function within the same source file.

Use cases

• Local static variables are often used when you need to maintain state or store information across multiple function calls within the same function.
• Global static variables are used when you want to limit the visibility of a variable to a single source file and ensure it retains its value throughout the program’s execution.

Example

In the following example the local static variable counter retains its value between calls to the example function, allowing it to count the number of function invocations.

#include <stdio.h>

void example(void)
{
    static int counter = 0;

    counter++;
    printf("Counter: %d\n", counter);
}

int main(void)
{
    example(); // Prints "Counter: 1"
    example(); // Prints "Counter: 2"
    example(); // Prints "Counter: 3"
    return (0);
}