Menu
×
   ❮   
HTML CSS JAVASCRIPT SQL PYTHON JAVA PHP HOW TO W3.CSS C C++ C# BOOTSTRAP REACT MYSQL JQUERY EXCEL XML DJANGO NUMPY PANDAS NODEJS R TYPESCRIPT ANGULAR GIT POSTGRESQL MONGODB ASP AI GO KOTLIN SASS VUE DSA GEN AI SCIPY AWS CYBERSECURITY DATA SCIENCE
     ❯   

C stdlib realloc() Function

❮ C stdlib Library


Example

Increase allocated memory:

// Allocate memory for a number of items
int numItems = 10;
int *myArray = malloc(numItems * sizeof(int));

// Write into the memory
for(int i = 0; i < numItems; i++) {
  myArray[i] = i + 1;
}

// Reallocate the memory
numItems = 20;
myArray = realloc(myArray, numItems * sizeof(int));

// Display the contents of the memory
for(int i = 0; i < numItems; i++) {
  printf("%d ", myArray[i]);
}

// Free the memory
free(myArray);
myArray = NULL;
Try it Yourself »

Definition and Usage

The realloc() function changes the size of a block of memory and returns a pointer to the block of memory. If there is not enough memory at the current location then the block of memory will be moved to a different location and a different pointer will be returned. The values in newly allocated memory are unpredictable.

The realloc() function is defined in the <stdlib.h> header file.

To learn more about memory allocation, see our C Memory Management tutorial.


Syntax

realloc(void * ptr, size_t size);

The size_t data type is a non-negative integer.

Parameter Values

Parameter Description
ptr Specifies a block of memory to be reallocated.
size Specifies the new size of the block of memory measured in bytes.

Technical Details

Returns: A void * pointer to the block of memory.

❮ C stdlib Library

×

Contact Sales

If you want to use W3Schools services as an educational institution, team or enterprise, send us an e-mail:
sales@w3schools.com

Report Error

If you want to report an error, or if you want to make a suggestion, send us an e-mail:
help@w3schools.com

W3Schools is optimized for learning and training. Examples might be simplified to improve reading and learning. Tutorials, references, and examples are constantly reviewed to avoid errors, but we cannot warrant full correctness of all content. While using W3Schools, you agree to have read and accepted our terms of use, cookie and privacy policy.

Copyright 1999-2024 by Refsnes Data. All Rights Reserved. W3Schools is Powered by W3.CSS.