Passing address, but it is working like call by value in C?

Question

Hello I am a beginner in C programming language. Recently I read about call by value and call by address. I have learned that in call by address changes in the called functi

Answer 1

The function is assigning a new address to the pointer but the pointer itself is being passed by value, as all arguments are in C. To change the value of a pointer variable the address of the pointer itself must be passed:

void change_by_add(int **ptr)
{
    *ptr = &y;
}

change_by_add(&p);

See C FAQ Question 4.8.

Passing by reference does not exist in C but can be achieved by passing the address of the variable who's value is to be changed to a function. For example:

void add_to_int(int* a_value, int a_increment)
{
    *a_value += a_increment;
}