malloc function - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the malloc function do in C?

The malloc function allocates a block of memory of a specified size on the heap and returns a pointer to the beginning of this block.

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What header file must be included to use malloc?

You must include the <stdlib.h> header file to use malloc in C.

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What does malloc return if it fails to allocate memory?

malloc returns NULL if it cannot allocate the requested memory.

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How do you properly free memory allocated by malloc?

You use the free function and pass the pointer returned by malloc to release the allocated memory back to the system.

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Example: What does this code do?<br>

int *p = malloc(5 * sizeof(int));

This code allocates memory for an array of 5 integers on the heap and stores the pointer to this memory in p. The cast to (int *) is not necessary in C and is omitted here.

What is the correct way to allocate memory for 10 doubles using malloc?

A malloc(10);

B malloc(10 * sizeof(int));

C malloc(10 * sizeof(double));

D malloc(sizeof(double));

You must multiply the number of elements (10) by the size of each element (sizeof(double)) to allocate enough memory.

If malloc fails, what value does it return?

A Garbage value

B 0

C -1

D NULL

malloc returns NULL to indicate failure to allocate memory.

Which header file is required to use malloc?

A <code>&lt;stdlib.h&gt;</code>

B <code>&lt;string.h&gt;</code>

C <code>&lt;stdio.h&gt;</code>

D <code>&lt;malloc.h&gt;</code>

The <stdlib.h> header contains the declaration for malloc.

What must you do after you finish using memory allocated by malloc?

A Nothing, it frees automatically

B Call <code>free</code> with the pointer

C Call <code>delete</code>

D Set pointer to NULL

You must call free to release the allocated memory and avoid memory leaks.

What type of pointer does malloc return?

A void *

B int *

C char *

D float *

malloc returns a void * pointer which can be cast to any other pointer type.

Explain how malloc works and why it is important in C programming.

Think about how programs get memory dynamically.

Describe the steps to safely allocate and free memory using malloc.

Consider what happens if malloc fails and how to avoid memory leaks.