1 .\" Copyright (c) 1993 by Thomas Koenig (ig25@rz.uni-karlsruhe.de)
3 .\" %%%LICENSE_START(VERBATIM)
4 .\" Permission is granted to make and distribute verbatim copies of this
5 .\" manual provided the copyright notice and this permission notice are
6 .\" preserved on all copies.
8 .\" Permission is granted to copy and distribute modified versions of this
9 .\" manual under the conditions for verbatim copying, provided that the
10 .\" entire resulting derived work is distributed under the terms of a
11 .\" permission notice identical to this one.
13 .\" Since the Linux kernel and libraries are constantly changing, this
14 .\" manual page may be incorrect or out-of-date. The author(s) assume no
15 .\" responsibility for errors or omissions, or for damages resulting from
16 .\" the use of the information contained herein. The author(s) may not
17 .\" have taken the same level of care in the production of this manual,
18 .\" which is licensed free of charge, as they might when working
21 .\" Formatted or processed versions of this manual, if unaccompanied by
22 .\" the source, must acknowledge the copyright and authors of this work.
25 .\" Modified Sat Jul 24 19:00:59 1993 by Rik Faith (faith@cs.unc.edu)
26 .\" Clarification concerning realloc, iwj10@cus.cam.ac.uk (Ian Jackson), 950701
27 .\" Documented MALLOC_CHECK_, Wolfram Gloger (wmglo@dent.med.uni-muenchen.de)
28 .\" 2007-09-15 mtk: added notes on malloc()'s use of sbrk() and mmap().
30 .TH MALLOC 3 2013-12-12 "GNU" "Linux Programmer's Manual"
32 malloc, free, calloc, realloc \- allocate and free dynamic memory
35 .B #include <stdlib.h>
37 .BI "void *malloc(size_t " "size" );
38 .BI "void free(void " "*ptr" );
39 .BI "void *calloc(size_t " "nmemb" ", size_t " "size" );
40 .BI "void *realloc(void " "*ptr" ", size_t " "size" );
48 bytes and returns a pointer to the allocated memory.
49 .IR "The memory is not initialized" .
56 or a unique pointer value that can later be successfully passed to
61 function frees the memory space pointed to by
63 which must have been returned by a previous call to
70 has already been called before, undefined behavior occurs.
73 is NULL, no operation is performed.
77 function allocates memory for an array of
81 bytes each and returns a pointer to the allocated memory.
82 The memory is set to zero.
91 or a unique pointer value that can later be successfully passed to
96 function changes the size of the memory block pointed to by
101 The contents will be unchanged in the range from the start of the region
102 up to the minimum of the old and new sizes.
103 If the new size is larger than the old size, the added memory will
108 is NULL, then the call is equivalent to
117 is not NULL, then the call is equivalent to
121 is NULL, it must have been returned by an earlier call to
126 If the area pointed to was moved, a
134 functions return a pointer to the allocated memory,
135 which is suitably aligned for any built-in type.
136 On error, these functions return NULL.
137 NULL may also be returned by a successful call to
142 or by a successful call to
152 function returns no value.
156 function returns a pointer to the newly allocated memory, which is suitably
157 aligned for any built-in type and may be different from
159 or NULL if the request fails.
162 was equal to 0, either NULL or a pointer suitable to be passed to
167 fails, the original block is left untouched; it is not freed or moved.
171 By default, Linux follows an optimistic memory allocation strategy.
174 returns non-NULL there is no guarantee that the memory really
176 In case it turns out that the system is out of memory,
177 one or more processes will be killed by the OOM killer.
178 For more information, see the description of
179 .IR /proc/sys/vm/overcommit_memory
181 .IR /proc/sys/vm/oom_adj
184 and the Linux kernel source file
185 .IR Documentation/vm/overcommit-accounting .
189 allocates memory from the heap, and adjusts the size of the heap
192 When allocating blocks of memory larger than
196 implementation allocates the memory as a private anonymous mapping using
199 is 128 kB by default, but is adjustable using
201 Allocations performed using
203 are unaffected by the
208 To avoid corruption in multithreaded applications,
209 mutexes are used internally to protect the memory-management
210 data structures employed by these functions.
211 In a multithreaded application in which threads simultaneously
212 allocate and free memory,
213 there could be contention for these mutexes.
214 To scalably handle memory allocation in multithreaded applications,
215 glibc creates additional
216 .IR "memory allocation arenas"
217 if mutex contention is detected.
218 Each arena is a large region of memory that is internally allocated
224 and managed with its own mutexes.
226 The UNIX 98 standard requires
236 Glibc assumes that this is done
237 (and the glibc versions of these routines do this); if you
238 use a private malloc implementation that does not set
240 then certain library routines may fail without having
250 are almost always related to heap corruption, such as overflowing
251 an allocated chunk or freeing the same pointer twice.
253 Recent versions of Linux libc (later than 5.4.23) and glibc (2.x)
256 implementation which is tunable via environment variables.
260 .\" http://g.oswego.edu/dl/html/malloc.html
261 .\" A Memory Allocator - by Doug Lea
263 .\" http://www.bozemanpass.com/info/linux/malloc/Linux_Heap_Contention.html
264 .\" Linux Heap, Contention in free() - David Boreham
266 .\" http://www.citi.umich.edu/projects/linux-scalability/reports/malloc.html
267 .\" malloc() Performance in a Multithreaded Linux Environment -
268 .\" Check Lever, David Boreham
275 .BR malloc_get_state (3),
278 .BR malloc_usable_size (3),
282 .BR posix_memalign (3)
284 This page is part of release 3.64 of the Linux
287 A description of the project,
288 and information about reporting bugs,
290 \%http://www.kernel.org/doc/man\-pages/.