eolas/zk/Pointers_in_C.md

tags
C

A pointer is a reference to the address of a variable in memory.

int x = 27;
int *ptr = &x;

printf("%i\n", x);
// 27


printf("%p\n", *ptr);
// 0x7ffeb44f7eac

The & and * is frankly confusing.

In the previous example, int *ptr = &x, ptr is a variable that holds the memory address of x. * signals that it is a pointer variable, & is what does the retrieval.

In the following:

int x = 27;
int *ptr = &x;
int value = *ptr;

We again set ptr to the memory address of x, but we use * on the last line to de-reference the pointer and get the original value back. Thus value becomes equal to 27.

Pointers are necessary because C uses a call by value system for function arguments.