eolas/zk/Pointers_in_C.md

---
tags:
  - C
---

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

```c
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:

```c
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](./C_is_call_by_value.md)
system for function arguments.