`calloc`

Article
02/07/2023

Allocates an array in memory with elements initialized to 0.

Syntax

void *calloc(
   size_t number,
   size_t size
);

Parameters

number
Number of elements.

size
Length in bytes of each element.

Return value

calloc returns a pointer to the allocated space. The storage space pointed to by the return value is suitably aligned for storage of any type of object. To get a pointer to a type other than void, use a type cast on the return value.

Remarks

The calloc function allocates storage space for an array of number elements, each of length size bytes. Each element is initialized to 0.

calloc sets errno to ENOMEM if a memory allocation fails or if the amount of memory requested exceeds _HEAP_MAXREQ. For information on this and other error codes, see errno, _doserrno, _sys_errlist, and _sys_nerr.

In the Microsoft implementation, if number or size is zero, calloc returns a pointer to an allocated block of non-zero size. An attempt to read or write through the returned pointer leads to undefined behavior.

calloc uses the C++ _set_new_mode function to set the new handler mode. The new handler mode indicates whether, on failure, calloc is to call the new handler routine as set by _set_new_handler. By default, calloc doesn't call the new handler routine on failure to allocate memory. You can override this default behavior so that, when calloc fails to allocate memory, it calls the new handler routine in the same way that the new operator does when it fails for the same reason. To override the default, call

_set_new_mode(1);

early in your program, or link with NEWMODE.OBJ (see Link options).

When the application is linked with a debug version of the C run-time libraries, calloc resolves to _calloc_dbg. For more information about how the heap is managed during the debugging process, see The CRT debug heap.

calloc is marked __declspec(noalias) and __declspec(restrict), meaning that the function is guaranteed not to modify global variables, and that the pointer returned isn't aliased. For more information, see noalias and restrict.

By default, this function's global state is scoped to the application. To change this behavior, see Global state in the CRT.

Requirements

Routine	Required header
`calloc`	`<stdlib.h>` and `<malloc.h>`

For more compatibility information, see Compatibility.

Example

// crt_calloc.c
// This program uses calloc to allocate space for
// 40 long integers. It initializes each element to zero.

#include <stdio.h>
#include <malloc.h>

int main( void )
{
   long *buffer;

   buffer = (long *)calloc( 40, sizeof( long ) );
   if( buffer != NULL )
      printf( "Allocated 40 long integers\n" );
   else
      printf( "Can't allocate memory\n" );
   free( buffer );
}

Allocated 40 long integers