Pointers: Addresses and the Null Contract

intermediate20 min readLesson 68 of 204

Pointers as optional object handles: dereferencing, const placement, and what a pointer parameter promises.

A pointer stores the address of an object (or nothing, when nullptr). Unlike a reference, a pointer can be reseated, compared, and incremented — and it can be null, which makes it the tool for "maybe no object".

int main_cj_pointer() {
    int value = 41;
    int* p = &value;          // p holds the address of value
    *p += 1;                  // dereference: value is now 42
    p = nullptr;              // p now points at nothing

    if (p) {                  // ALWAYS check before dereferencing
        std::cout << *p;
    }
    return 0;
}

Reading pointer declarations out loud

int* p — "p is a pointer to int".
const int* p — pointer to const int: the pointee is read-only.
int* const p — const pointer to int: the pointer cannot reseat.
const int* const p — neither pointer nor pointee may change.

Read the declaration from right to left and const never surprises you.

Pointer + const& decide most interfaces

void rename(std::string* out, const std::string& fallback);
// out: optional (caller may pass nullptr) and written through
// fallback: required, read-only

A reference says "I need an object". A pointer says "I might not get one". Document which contract each parameter has.

Now practice

Pointers and the null contractHandle optional objects honestly: sum through possibly-null pointers, return an optional max.2 challenges · · ~25 min