Allocate space for an array


#include <stdlib.h>

void* calloc ( size_t n, 
               size_t size );


The number of array elements to allocate.
The size, in bytes, of one array element.



Use the -l c option to qcc to link against this library. This library is usually included automatically.


The calloc() function allocates space from the heap for an array of n objects, each of size bytes, and initializes them to 0. Use free() or realloc() to free the block of memory.

Because the malloc() implementation uses signed, 32-bit integers to represent the size internally, you can't allocate more than 2 GB in a single allocation. If the size is greater than 2 GB, calloc() indicates an error of ENOMEM.

If n or size is zero, the default behavior is to return a non-NULL pointer that's valid only to a corresponding call to free() or realloc(). Don't assume that this pointer points to any valid memory. You can control this behavior via the MALLOC_OPTIONS environmental variable; if the value of MALLOC_OPTIONS contains a V, calloc() returns a NULL pointer. This environment variable also affects malloc() and realloc(). This is known as the "System V" behavior.


A pointer to the start of the allocated memory, or NULL if an error occurred ( errno is set).


Not enough memory.
No error.


#include <stdlib.h>
#include <stdio.h>

int main( void )
    char* buffer;

    buffer = (char* )calloc( 80, sizeof(char) );
    if( buffer == NULL ) {
        printf( "Can't allocate memory for buffer!\n" );
        return EXIT_FAILURE;

    free( buffer );

    return EXIT_SUCCESS;

Environment variables:

Control the way calloc(), malloc(), and realloc() behave if you specify a size of 0 (or a value of 0 for the n argument to calloc()). The V ("System V") and R ("use the realloc() behavior of QNX Neutrino 6.4.0 and earlier") columns below indicate how the functions behave if the value of MALLOC_OPTIONS includes that letter:
Function Default V R
calloc(n, 0) Non-NULL NULL No effect
malloc(0) Non-NULL NULL No effect
realloc(NULL, 0) Non-NULL NULL No effect
realloc(non-NULL, 0) Non-NULL NULL NULL

In all the above cases, if the function returns a non-NULL pointer, it's valid only for a corresponding call to free() or realloc().


ANSI, POSIX 1003.1

Cancellation point No
Interrupt handler No
Signal handler No
Thread Yes

Last modified: 2013-12-23

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