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.
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: the value returned shall be
either a null pointer or a unique pointer.
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 or a unique pointer
value that can be successfully passed to free() shall be returned.
Otherwise, it shall return a null pointer and set errno to indicate
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The Open
Group Base Specifications Issue 7, Copyright (C) 2013 by the
Institute of Electrical and Electronics Engineers, Inc and The Open
Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
applied.) 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.unix.org/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
IEEE/The Open Group 2013 CALLOC(3P)