1.\" 2.\" The contents of this file are subject to the terms of the 3.\" Common Development and Distribution License (the "License"). 4.\" You may not use this file except in compliance with the License. 5.\" 6.\" You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE 7.\" or http://www.opensolaris.org/os/licensing. 8.\" See the License for the specific language governing permissions 9.\" and limitations under the License. 10.\" 11.\" When distributing Covered Code, include this CDDL HEADER in each 12.\" file and include the License file at usr/src/OPENSOLARIS.LICENSE. 13.\" If applicable, add the following below this CDDL HEADER, with the 14.\" fields enclosed by brackets "[]" replaced with your own identifying 15.\" information: Portions Copyright [yyyy] [name of copyright owner] 16.\" 17.\" 18.\" Copyright 1989 AT&T 19.\" Copyright (c) 2005, Sun Microsystems, Inc. All Rights Reserved. 20.\" Copyright 2017 Nexenta Systems, Inc. 21.\" 22.Dd July 28, 2017 23.Dt MALLOC 3C 24.Os 25.Sh NAME 26.Nm malloc , 27.Nm calloc , 28.Nm free , 29.Nm freezero , 30.Nm memalign , 31.Nm realloc , 32.Nm reallocarray , 33.Nm recallocarray , 34.Nm valloc , 35.Nm alloca 36.Nd memory allocator 37.Sh SYNOPSIS 38.In stdlib.h 39.Ft void * 40.Fo malloc 41.Fa "size_t size" 42.Fc 43.Ft void * 44.Fo calloc 45.Fa "size_t nelem" 46.Fa "size_t elsize" 47.Fc 48.Ft void 49.Fo free 50.Fa "void *ptr" 51.Fc 52.Ft void 53.Fo freezero 54.Fa "void *ptr" 55.Fa "size_t size" 56.Fc 57.Ft void * 58.Fo memalign 59.Fa "size_t alignment" 60.Fa "size_t size" 61.Fc 62.Ft void * 63.Fo realloc 64.Fa "void *ptr" 65.Fa "size_t size" 66.Fc 67.Ft void * 68.Fo reallocarray 69.Fa "void *ptr" 70.Fa "size_t nelem" 71.Fa "size_t elsize" 72.Fc 73.Ft void * 74.Fo recallocarray 75.Fa "void *ptr" 76.Fa "size_t oldnelem" 77.Fa "size_t newnelem" 78.Fa "size_t elsize" 79.Fc 80.Ft void * 81.Fo valloc 82.Fa "size_t size" 83.Fc 84.In alloca.h 85.Ft void * 86.Fo alloca 87.Fa "size_t size" 88.Fc 89.Sh DESCRIPTION 90The 91.Fn malloc 92and 93.Fn free 94functions provide a simple, general-purpose memory allocation package. 95The 96.Fn malloc 97function returns a pointer to a block of at least 98.Fa size 99bytes suitably aligned for any use. 100If the space assigned by 101.Fn malloc 102is overrun, the results are undefined. 103.Pp 104The argument to 105.Fn free 106is a pointer to a block previously allocated by 107.Fn malloc , 108.Fn calloc , 109.Fn realloc , 110.Fn reallocarray , 111or 112.Fn recallocarray . 113After 114.Fn free 115is executed, this space is made available for further allocation by the 116application, though not returned to the system. 117Memory is returned to the system only upon termination of the application. 118If 119.Fa ptr 120is a null pointer, no action occurs. 121If a random number is passed to 122.Fn free , 123the results are undefined. 124.Pp 125The 126.Fn freezero 127function is similar to the 128.Fn free 129function except it ensures memory is explicitly discarded. 130If 131.Fa ptr 132is 133.Dv NULL , 134no action occurs. 135If 136.Fa ptr 137is not 138.Dv NULL , 139the 140.Fa size 141argument must be equal or smaller than the size of the earlier allocation that 142returned 143.Fa ptr . 144.Fn freezero 145guarantees the memory range starting at 146.Fa ptr 147with length 148.Fa size 149is discarded while deallocating the whole object originally allocated. 150.Pp 151The 152.Fn calloc 153function allocates space for an array of 154.Fa nelem 155elements of size 156.Fa elsize . 157The space is initialized to zeros. 158.Pp 159The 160.Fn memalign 161function allocates 162.Fa size 163bytes on a specified alignment boundary and returns a pointer to the allocated 164block. 165The value of the returned address is guaranteed to be an even multiple of 166.Fa alignment . 167The value of 168.Fa alignment 169must be a power of two and must be greater than or equal to the size of a word. 170.Pp 171The 172.Fn realloc 173function changes the size of the block pointed to by 174.Fa ptr 175to 176.Fa size 177bytes and returns a pointer to the 178.Pq possibly moved 179block. 180The contents will be unchanged up to the lesser of the new and old sizes. 181If the new size of the block requires movement of the block, the space for the 182previous instantiation of the block is freed. 183If the new size is larger, the contents of the newly allocated portion of the 184block are unspecified. 185If 186.Fa ptr 187is 188.Dv NULL , 189.Fn realloc 190behaves like 191.Fn malloc 192for the specified size. 193If 194.Fa size 195is 0 and 196.Fa ptr 197is not a null pointer, the space pointed to is freed. 198.Pp 199The 200.Fn reallocarray 201function is similar to 202.Fn realloc , 203but operates on 204.Fa nelem 205elements of size 206.Fa elsize 207and checks for overflow in 208.Fa nelem Ns * Ns Fa elsize 209calculation. 210.Pp 211The 212.Fn recallocarray 213function is similar to 214.Fn reallocarray 215except it ensures newly allocated memory is cleared similar to 216.Fn calloc . 217If 218.Fa ptr 219is 220.Dv NULL , 221.Fa oldnelem 222is ignored and the call is equivalent to 223.Fn calloc . 224If 225.Fa ptr 226is not 227.Dv NULL , 228.Fa oldnelem 229must be a value such that 230.Fa oldnelem Ns * Ns Fa elsize 231is the size of the earlier allocation that returned 232.Fa ptr , 233otherwise the behaviour is undefined. 234.Pp 235The 236.Fn valloc 237function has the same effect as 238.Fn malloc , 239except that the allocated memory will be aligned to a multiple of the value 240returned by 241.Nm sysconf Ns Pq Dv _SC_PAGESIZE . 242.Pp 243The 244.Fn alloca 245function allocates 246.Fa size 247bytes of space in the stack frame of the caller, and returns a pointer to the 248allocated block. 249This temporary space is automatically freed when the caller returns. 250If the allocated block is beyond the current stack limit, the resulting behavior 251is undefined. 252.Sh RETURN VALUES 253Upon successful completion, each of the allocation functions returns a pointer 254to space suitably aligned 255.Pq after possible pointer coercion 256for storage of any type of object. 257.Pp 258If there is no available memory, 259.Fn malloc , 260.Fn calloc , 261.Fn realloc , 262.Fn reallocarray , 263.Fn recallocarray , 264.Fn memalign , 265and 266.Fn valloc 267return a null pointer. 268.Pp 269When 270.Fn realloc 271is called with 272.Fa size 273> 0 and returns 274.Dv NULL , 275the block pointed to by 276.Fa ptr 277is left intact. 278If 279.Fa size , 280.Fa nelem , 281or 282.Fa elsize 283is 0, either a null pointer or a unique pointer that can be passed to 284.Fn free 285is returned. 286.Pp 287If 288.Fn malloc , 289.Fn calloc , 290.Fn realloc , 291.Fn reallocarray , 292or 293.Fn recallocarray 294returns unsuccessfully, 295.Va errno 296will be set to indicate the error. 297The 298.Fn free 299and 300.Fn freezero 301functions do not set 302.Va errno . 303.Sh ERRORS 304The 305.Fn malloc , 306.Fn calloc , 307.Fn realloc , 308and 309.Fn reallocarray 310functions will fail if: 311.Bl -tag -width Er 312.It Er ENOMEM 313The physical limits of the system are exceeded by 314.Fa size 315bytes of memory which cannot be allocated, or there's integer overflow in 316.Fn reallocarray . 317.It Er EAGAIN 318There is not enough memory available to allocate 319.Fa size 320bytes of memory; but the application could try again later. 321.El 322.Pp 323The 324.Fn recallocarray 325function will fail if: 326.Bl -tag -width Er 327.It Er EINVAL 328.Fa ptr 329is not 330.Dv NULL 331and multiplying 332.Fa oldnelem 333and 334.Fa elsize 335results in integer overflow. 336.El 337.Sh USAGE 338Portable applications should avoid using 339.Fn valloc 340but should instead use 341.Fn malloc 342or 343.Xr mmap 2 . 344On systems with a large page size, the number of successful 345.Fn valloc 346operations might be 0. 347.Pp 348These default memory allocation routines are safe for use in multithreaded 349applications but are not scalable. 350Concurrent accesses by multiple threads are single-threaded through the use of a 351single lock. 352Multithreaded applications that make heavy use of dynamic memory allocation 353should be linked with allocation libraries designed for concurrent access, such 354as 355.Xr libumem 3LIB 356or 357.Xr libmtmalloc 3LIB . 358Applications that want to avoid using heap allocations 359.Pq with Xr brk 2 360can do so by using either 361.Xr libumem 3LIB 362or 363.Xr libmapmalloc 3LIB . 364The allocation libraries 365.Xr libmalloc 3LIB 366and 367.Xr libbsdmalloc 3LIB 368are available for special needs. 369.Pp 370Comparative features of the various allocation libraries can be found in the 371.Xr umem_alloc 3MALLOC 372manual page. 373.Sh INTERFACE STABILITY 374The 375.Fn malloc , 376.Fn calloc , 377.Fn free , 378.Fn realloc , 379.Fn valloc 380functions are 381.Sy Standard. 382.Pp 383The 384.Fn freezero , 385.Fn reallocarray , 386and 387.Fn recallocarray 388functions are 389.Sy Committed . 390.Pp 391The 392.Fn memalign 393and 394.Fn alloca 395functions are 396.Sy Stable . 397.Sh MT-LEVEL 398.Sy Safe. 399.Sh SEE ALSO 400.Xr brk 2 , 401.Xr getrlimit 2 , 402.Xr libbsdmalloc 3LIB , 403.Xr libmalloc 3LIB , 404.Xr libmapmalloc 3LIB , 405.Xr libmtmalloc 3LIB , 406.Xr libumem 3LIB , 407.Xr umem_alloc 3MALLOC , 408.Xr watchmalloc 3MALLOC , 409.Xr attributes 5 410.Sh WARNINGS 411Undefined results will occur if the size requested for a block of memory 412exceeds the maximum size of a process's heap, which can be obtained with 413.Xr getrlimit 2 . 414.Pp 415The 416.Fn alloca 417function is machine-, compiler-, and most of all, system-dependent. 418Its use is strongly discouraged. 419