Pointers

Pointer

A pointer refers to the memory address of a variable.

The pointer of a variable is referred to using the address operator &.

String formatting

%p is used to specify the addresses, which are printed out in hexadecimal format.

printf("a = %d", a) prints the value of a in decimal. printf(&a = %p", a) prints the address of a.

To store an address of another variable, use a pointer variable. The variable is then considered to be pointing to the variable with the memory address.

Example

int a;
int *a_ptr = a;

The indirection operator * allows access of the value of a pointer variable. In the example above, then a is synonymous with *a_ptr

Incrementing Pointer

Incrementing a pointer results in an incrementation of the address by the size of the data type that the pointer is referring to. For example, if a pointer for an int variable (which takes up 4 bytes) is incremented, the address it is pointed to is incremented by 4 bytes.

Example

int a;
int *b = &a; // if the memory address here is ffbff0a4
 
*b++; // it increments by 4 to ffbff0a8

Common sizes for data types

int: 4 bytes float: 8 bytes char: 1 byte double: 8 bytes

Segmentation Fault

Do not use the indirection operator to access the value of a non-initialised pointer variable, as this will cause a segmentation fault. An example of this:

Example

int *n;
*n = 123;

Use Cases

• Pass addresses of two or more variables so function can pass back to caller new values for variables
• Pass address of first element of array to a function so function can access all elements in array.