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PROLOG
This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface
may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface
may not be implemented on Linux.
NAME
calloc — a memory allocator
SYNOPSIS
#include <stdlib.h> void *calloc(size_t nelem, size_t elsize);
DESCRIPTION
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.1‐2017 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 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 and set errno to indicate the error.
ERRORS
The calloc() function shall fail if:
ENOMEM 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()
The Base Definitions volume of POSIX.1‐2017, <stdlib.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard
for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original
IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document.
The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .
Any typographical or formatting errors that appear in this page are most likely to have been introduced
during the conversion of the source files to man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .