C

Introduction

Types

Conditional

Iteration

Memory management

Pointers

A pointer is a variable that stores a memory location (or an address of a variable).

datatype *ptr_name;

Example:

int *ptr;

Operators

* (asterisk)

The unary operator * (asterisk) is used for two things:

• To declare a pointer variable (see example above);

• To access the value stored in a pointer. This is called "deferencing".

& (ampersand)

To get the address of a variable, we use the unary operator & (ampersand). For example, &x gives us the address of variable x.

Example:

int x = 5; // variable declaration
int *ptr; // pointer declaration
ptr = &x; // pointer assignment
printf("%d", *ptr); // prints 5 by dereferencing ptr

Dynamic memory allocation

malloc()

Allocate memory in the heap.

type *ptr = (type*) malloc(byte_size * sizeof *ptr)

Example:

int *ptr = (int*) malloc(10 * sizeof *ptr);

calloc()

Allocate memory in the heap and initialize it to zero.

type *ptr = (type*) calloc(num_elements, element_size)

Example:

int *ptr = (int*) calloc(10, sizeof *ptr);

realloc()

Reallocate memory in the heap.

type *ptr = (type*) realloc(ptr, new_size)

Example:

int *ptr = (int*) malloc(10 * sizeof *ptr);
ptr = (int*) realloc(ptr, 20 * sizeof ptr);

free()

Free memory in the heap.

free(ptr)

Tips

• Always check if allocation was successful:

int *ptr = (int*) malloc(10 * sizeof *ptr);
if (!ptr)
{
    fprintf(stderr, "Memory allocation failed");
    exit(EXIT_FAILURE);
}

• It must be as mallocs or callocs as frees;

• Don't forget to count the null terminator when allocating memory for strings.

Functions

Structures

Multi-file