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Note

C: Storage Classes

What a storage class is, using static to persist a variable's value across calls, and extern for cross-file globals.

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#include <stdio.h>
/* A class of storing variables. It tells the compiler where to store the data. ie-stack or heap. Or if variable data storage is already declared elsewhere */


void print_plus_one(void){
    static int a = 0; /* static storage class */
    printf("%d\n", a);


    a++; /* increment the static value*/
}


int main(void){
    print_plus_one(); /* prints "0" */
    print_plus_one(); /* prints "1" */
    print_plus_one(); /* prints "2" */
    print_plus_one(); /* prints "3" */


    return 0;
}




/* Note that, normally the variable a will only be local to the print_plus_one function, and be stored on the stack. But using the "static" keyword it tells the compiler to store it on the heap instead. Hence making it behave more like a global variable. */




/* There's another storage class called "extern", which tells the compiler that the definition of the variable is in a different file. This allows you to reference a global variable from a file even if its defined somewhere else. */