[ int const * ] vs [ int * const ] vs [ int * const * ]

Consts.h

/**
 * Most common & obvious usage
 */
void constInt () {
    int const x = 0;  // the x variable can not be modified
    const int y = 0;  // this has the same meaning
}

/**
 * A "constant pointer" to a changeable integer
 */
void constPointerToInt () {
    int a = 1;
    int b = 2;
    int * const c = &a;

    // The value of the integer pointed to by 'z' is changeable, but 'z'
    // cannot be reassigned.  This is valid:
    *c = 12345;

    // But this is NOT valid. I can't re-assign the pointer to another address:
    c = &b;  // Error: read-only variable is not assignable
}

/*
 * A changeable pointer to a 'constant integer'
 */
void pointerToConstInt () {

    // Given:
    int a = 1;
    int b = 2;
    int const * c = &a;

    // I can change WHERE c points to:
    c = &b;

    // But I cannot change the value at that address
    *c = 123;    // Error: Read-only variable is not assignable
}


/*
 * A CONSTANT pointer to a CONSTANT integer
 */
void constPointerToConstInt () {
    
    // Given:
    int a = 1;
    int b = 2;

    int const * const c = &a; // Notice the double-use of 'const'

    // I cannot modify WHERE 'c' points
    c = &b;      // Error: Read-only variable is not assignable

    // NOR can I modify the value it poitns to:
    *c = 123;    // Error: Read-only variable is not assignable
}