Question

Explain the difference in the C memory model between global and local variables. How is each allocated and accessed?

Answer 1

There are 4 sections in memory: data, heap, stack, and code.

In C, There are 2 kind of variables that get created.. The local and the global variables.. The local variables are created on the stack, while the global variables are created in the data section. The global variables can be accessed from anywhere in the coe and their values can be changed as well by any piece of code.. While the local variables are accessible only in the scope of the function, which is containing the variable declaration..

Here is an example:

int myGlobal = 5;

void func1() {
        
        int temp = 1; // This is a local variable only accessible in func1
        printf("Temp: %d\n", temp);
        
        // we can change the value of temp as well here.
}

int main() {
        
        // We can read the value of global variable here, as well as change it.
        printf("Global: %d\n", myGlobal);

        myGlobal = 10;
        printf("Global: %d\n", myGlobal);
        
        func1();
        
        // At this point, our call to func1 is completed, and thus temp variable
        // is not anymore present.
}

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