Static Variables in C

In C, the static keyword has multiple uses, but fundamentally, it affects the storage duration and linkage of a variable or function.

When you declare a variable with static inside a function or globally, you're influencing these aspects:

Storage Duration

• Static Storage Duration: Variables declared as static have a lifespan that extends across the entire runtime of the program.
  • This is different from automatic variables (those declared without static inside functions), which are created and destroyed each time the function is called.
  • This means static variables maintain their value between function calls.

Linkage

• Internal Linkage: When static is used with global variables or functions, it restricts their visibility to the file in which they are declared.
  • This means they cannot be accessed or linked from other files, which helps in encapsulating the code and avoiding name conflicts across different files.

Zero-Initialization

#include <stdio.h>

int main() {
    static int some_num;
    printf("%d\n", some_num);  // 0
    return 0;
}

• static variables are automatically zero-initialized if they're not explicitly initialized.

  • This includes those defined inside functions.

• This ensures that they start from a known state, which is useful for variables that are meant to maintain their state across function calls or throughout the program's execution.