Pointer

A pointer is a variable that stores the memory address of another variable. Declare a pointer by specifying the variable type followed by an asterisk *:

int* ptr;

The address of a variable is obtained with the address-of operator (&):

int var = 1;
int* ptr = &var;

The value at the address is accessed with the dereference operator (*). Reading and writing through the pointer reads and writes the original variable:

std::cout << *ptr << "\n";  // 1
*ptr = 2;
std::cout << var << "\n";   // 2

A pointer can be reassigned to point at a different variable:

int a = 1;
int b = 2;
int* ptr = &a;
ptr = &b;
*ptr = 3;  // b is now 3, a is unchanged.

Members of a pointed-to object are accessed with the stab operator (->), which is syntactic sugar for dereferencing then using the dot operator:

struct Point { int x; int y; };

Point p = {1, 2};
Point* ptr = &p;
ptr->x = 5;   // Same as (*ptr).x = 5;

const can apply to the pointed-to value, the pointer itself, or both:

int var = 1;
const int* a = &var;        // Cannot modify *a, can reassign a.
int* const b = &var;        // Can modify *b, cannot reassign b.
const int* const c = &var;  // Cannot modify *c, cannot reassign c.

A null pointer can be assigned by using the nullptr keyword and can be checked before dereferencing:

int* ptr = nullptr;

if (ptr != nullptr) {
  *ptr = 1;
}