Difference Wiki

Malloc vs. Calloc: What's the Difference?

Edited by Aimie Carlson || By Janet White || Published on February 22, 2024
Malloc allocates uninitialized memory, while calloc allocates zero-initialized memory; both are used for dynamic memory allocation in C.

Key Differences

Malloc (Memory Allocation) is a function used in C programming for dynamic memory allocation, allocating a specified number of bytes. Calloc (Contiguous Allocation) also allocates memory dynamically, but it initializes the allocated memory to zero. This initialization is the key difference between malloc and calloc.
Malloc takes a single argument: the total size in bytes to allocate, and it returns a pointer to the beginning of the allocated memory. Calloc, on the other hand, takes two arguments: the number of elements and the size of each element, and it allocates contiguous memory for the array, initializing all bits to zero.
The memory block allocated by malloc contains garbage values as it does not initialize the allocated memory. This could lead to unpredictable behavior if the memory is accessed before being explicitly initialized. Calloc, by initializing the memory, avoids such issues, providing a block of memory with all zeros.
Malloc is generally faster than calloc because it does not set the allocated memory to zero. For scenarios where initialization is not necessary, malloc is preferred. Calloc is used when memory needs to be zero-initialized, especially important for array allocation and structures.
Error handling in both functions is similar; they return a NULL pointer if the memory allocation fails. However, calloc's additional step of initializing memory might make it slightly slower and more resource-intensive compared to malloc.

Comparison Chart


Allocates memory without initialization
Allocates memory and initializes to zero

Function Arguments

Takes one argument: total size in bytes
Takes two arguments: number and size of elements


Generally faster, as no initialization is performed
Slower due to initialization process

Use Cases

Preferred when initialization is not necessary
Used when zero-initialization is needed

Memory Contents

Contains garbage values initially
Contains all zeros initially

Malloc and Calloc Definitions


Faster than calloc as it skips initialization.
Malloc(2048); for rapid allocation of 2048 bytes.


Calloc allocates and initializes memory to zero.
Int *array = calloc(10, sizeof(int)); creates an array of 10 integers, all initialized to zero.


Malloc allocates a specified size of memory dynamically.
Int *array = malloc(10 * sizeof(int)); allocates memory for an array of 10 integers.


Slower than malloc due to initialization.
Calloc(100, sizeof(char)); for a zero-initialized char array.


Does not initialize the allocated memory.
Char *buffer = malloc(50); allocates 50 bytes without initialization.


Takes two arguments for allocation.
Float *matrix = calloc(4, sizeof(float)); allocates and zeroes a float array.


Suitable for when initialization is not needed.
Double *values = malloc(5 * sizeof(double)); for quick allocation.


Eliminates the need for manual initialization.
Char *string = calloc(50, sizeof(char)); ensures a zeroed string.


Requires manual initialization if needed.
Int *nums = malloc(100 * sizeof(int)); followed by a loop to initialize.


Preferred for safety in array and structure allocation.
Struct Point *points = calloc(5, sizeof(struct Point)); for initializing structures.


(computing) A subroutine in the C programming language's standard library for performing dynamic memory allocation.


(computing) To allocate memory using the C programming language malloc subroutine.


What is malloc used for?

For dynamic memory allocation without initialization.

Does calloc return NULL on failure?

Yes, similar to malloc.

How do malloc and calloc handle memory allocation errors?

Both return a NULL pointer on failure.

Can malloc and calloc memory be resized?

Yes, using realloc.

When should I use calloc over malloc?

When you need memory to be zero-initialized.

How many arguments does calloc require?

Two arguments: the number of elements and size of each.

Is it necessary to free memory allocated by malloc and calloc?

Yes, to avoid memory leaks.

In what scenarios is calloc preferable?

In scenarios where initialized memory is important for safety.

What is calloc used for?

For dynamic memory allocation with zero-initialization.

Is malloc faster than calloc?

Yes, as it doesn't initialize memory.

How many arguments does malloc take?

One argument: the size in bytes.

What type of data can malloc allocate?

Any type, as it allocates raw memory.

Can the memory allocated by malloc contain random values?

Yes, it contains garbage values initially.

What happens if malloc fails?

It returns NULL.

Can calloc be used for non-zero initialization?

No, it only initializes memory to zero.

Are malloc and calloc interchangeable?

They can be, but their use depends on initialization needs.

Do malloc and calloc allocate memory from the heap?

Yes, both allocate memory from the heap.

What type of applications commonly use malloc?

Applications that require dynamic memory management.

Does calloc's initialization affect performance?

Yes, it can be slower due to zero-initialization.

Is zero-initialization the main difference between malloc and calloc?

Yes, that's the key distinction.
About Author
Written by
Janet White
Janet White has been an esteemed writer and blogger for Difference Wiki. Holding a Master's degree in Science and Medical Journalism from the prestigious Boston University, she has consistently demonstrated her expertise and passion for her field. When she's not immersed in her work, Janet relishes her time exercising, delving into a good book, and cherishing moments with friends and family.
Edited by
Aimie Carlson
Aimie Carlson, holding a master's degree in English literature, is a fervent English language enthusiast. She lends her writing talents to Difference Wiki, a prominent website that specializes in comparisons, offering readers insightful analyses that both captivate and inform.

Trending Comparisons

Popular Comparisons

New Comparisons