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.
malloc — a memory allocator
void *malloc(size_t size);
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 malloc() function shall allocate unused space for an
object whose size in bytes is specified by size and whose value is
The order and contiguity of storage allocated by successive calls
to malloc() 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 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 points 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 size not equal to 0, malloc()
shall return a pointer to the allocated space. If size is 0, either a
null pointer or a unique pointer that can be successfully passed to
free() shall be returned. Otherwise, it shall return a null pointer and
set errno to indicate the error.
The malloc() function shall fail if:
- Insufficient storage space is available.
The following sections are informative.
calloc(), free(), getrlimit(),
The Base Definitions volume of POSIX.1‐2008,
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 .
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