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PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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CALLOC(3P) POSIX Programmer's Manual CALLOC(3P)
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.
calloc — a memory allocator
#include <stdlib.h>
void *calloc(size_t nelem, size_t elsize);
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.
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.
The calloc() function shall fail if:
ENOMEM Insufficient memory is available.
The following sections are informative.
None.
There is now no requirement for the implementation to support the
inclusion of <malloc.h>.
None.
None.
free(3p), malloc(3p), realloc(3p)
The Base Definitions volume of POSIX.1‐2017, stdlib.h(0p)
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 .
IEEE/The Open Group 2017 CALLOC(3P)
Pages that refer to this page: stdlib.h(0p), free(3p), malloc(3p), realloc(3p)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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