Lesson 8

Simulate pass by reference

• When we pass a variable, we pass the variable to the function. When we pass the address, we simulate pass-by-reference.

  • void pass_by_value(int a); copies the value into the function

  • void pass_by_reference(int *a); passes the address into the function affecting the original value if the function changes it.

• If we don’t plan on change the reference, we can simply use the const keyword (void pass_by_reference(const int *a);).

• A common pattern is to use pointers to bring back a value from the function:

    /*
    Return larger value, extract the smallest value via pointer
    */
    int max_min(int a, int b, int *smallest) {
        if (a > b) {
            *smallest = b;
            return a;
        }
  
        *smallest = a;
        return b;
    }
  

Array of pointers

• int arr[3] is an array of integers.

    int arr[3] = {1, 2, 3};
    printf("%d\n", arr[0]); // prints 1
  

• int *arr[3]; is an array of integer pointers.

    int arr[3] = {1, 2, 3};
    int *arrp[3] = {arr, arr + 1, arr + 2};
    printf("%d\n", *arrp[0]); // prints 1
  

• int (*arr)[3]; is a pointer that points to an array of 3 integers.

    int arr[3] = {1, 2, 3};
    int (*arrp)[3] = &arr;
    printf("%d\n", (*arrp)[0]); // prints 1
  

Pointer to pointer

• We can pointer to another pointer

    int a = 3;
    int *b = &a;
    int **c = &b;
    int ***d = &c;