The Open Group Base Specifications Issue 7
IEEE Std 1003.1-2008, 2016 Edition
Copyright © 2001-2016 The IEEE and The Open Group

#### NAME

> calloc - a memory allocator

#### SYNOPSIS

> ``#include <stdlib.h>
> void *calloc(size_t` nelem`, size_t` elsize`);
> ``

#### DESCRIPTION

> [CX] The functionality described on this reference page is aligned with the ISO C standard. Any conflict between the requirements described here and the ISO C standard is unintentional. This volume of POSIX.1-2008 defers to the ISO C standard.

> The calloc() function shall allocate unused space for an array of nelem elements each of whose size in bytes is elsize. The space shall be initialized to all bits 0.

> The order and contiguity of storage allocated by successive calls to calloc() is unspecified. The pointer returned if the allocation succeeds shall be suitably aligned so that it may be assigned to a pointer to any type of object and then used to access such an object or an array of such objects in the space allocated (until the space is explicitly freed or reallocated). Each such allocation shall yield a pointer to an object disjoint from any other object. The pointer returned shall point to the start (lowest byte address) of the allocated space. If the space cannot be allocated, a null pointer shall be returned. If the size of the space requested is 0, the behavior is implementation-defined: either a null pointer shall be returned, or the behavior shall be as if the size were some non-zero value, except that the behavior is undefined if the returned pointer is used to access an object.

#### RETURN VALUE

> Upon successful completion with both nelem and elsize non-zero, calloc() shall return a pointer to the allocated space. If either nelem or elsize is 0, then either:

> - A null pointer shall be returned [CX] and errno may be set to an implementation-defined value, or

> - A pointer to the allocated space shall be returned. The application shall ensure that the pointer is not used to access an object.

> Otherwise, it shall return a null pointer [CX] and set errno to indicate the error.

#### ERRORS

> The calloc() function shall fail if:

> [ENOMEM]
>   [CX] Insufficient memory is available.

The following sections are informative.

#### EXAMPLES

> None.

#### APPLICATION USAGE

> There is now no requirement for the implementation to support the inclusion of <malloc.h>.

#### RATIONALE

> None.

#### FUTURE DIRECTIONS

> None.

#### SEE ALSO

> free, malloc, realloc

> XBD <stdlib.h>

#### CHANGE HISTORY

> First released in Issue 1. Derived from Issue 1 of the SVID.

#### Issue 6

> Extensions beyond the ISO C standard are marked.

> The following new requirements on POSIX implementations derive from alignment with the Single UNIX Specification:

> - The setting of errno and the [ENOMEM] error condition are mandatory if an insufficient memory condition occurs.

#### Issue 7

> POSIX.1-2008, Technical Corrigendum 2, XSH/TC2-2008/0053 [526] is applied.

End of informative text.

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