# Pointer to Pointer & NULL — C Programming

Source: https://www.geekswithgeeks.com/en/c/c-pointer-advanced

> Indirection, one more level, and how pointers fail safely.

## A pointer to a pointer

`int **pp` holds the address of an `int *`. Dereferencing once (`*pp`) gives the inner pointer; twice (`**pp`) gives the actual int. Common in dynamic 2D arrays and functions that need to reassign a caller's pointer.

## NULL means "points nowhere"

An uninitialised pointer holds garbage. Assigning `NULL` explicitly marks it as pointing nowhere, and it's good practice to check before dereferencing.

```c
int *p = NULL;

if (p != NULL) {
    printf("%d\n", *p);
} else {
    printf("p points nowhere\n");
}
```

Output:

```
p points nowhere
```

## Two classic pointer bugs

**Wild pointer**: used before being assigned a valid address. **Dangling pointer**: still points to memory that has already been freed. Both cause undefined behavior — always initialise, and set to `NULL` after freeing.