'\" te .\" Portions Copyright (c) 2005, 2015, Oracle and/or its affiliates. All rights reserved. .\" Copyright 1989 AT&T .TH malloc 3C "9 Apr 2015" "SunOS 5.11" "Standard C Library Functions" .SH NAME malloc, calloc, free, memalign, realloc, valloc, alloca \- memory allocator .SH SYNOPSIS .LP .nf #include \fBvoid *\fR\fBmalloc\fR(\fBsize_t\fR \fIsize\fR); .fi .LP .nf \fBvoid *\fR\fBcalloc\fR(\fBsize_t\fR \fInelem\fR, \fBsize_t\fR \fIelsize\fR); .fi .LP .nf \fBvoid\fR \fBfree\fR(\fBvoid *\fR\fIptr\fR); .fi .LP .nf \fBvoid *\fR\fBmemalign\fR(\fBsize_t\fR \fIalignment\fR, \fBsize_t\fR \fIsize\fR); .fi .LP .nf \fBvoid *\fR\fBrealloc\fR(\fBvoid *\fR\fIptr\fR, \fBsize_t\fR \fIsize\fR); .fi .LP .nf \fBvoid *\fR\fBvalloc\fR(\fBsize_t\fR \fIsize\fR); .fi .LP .nf #include \fBvoid *\fR\fBalloca\fR(\fBsize_t\fR \fIsize\fR); .fi .SH DESCRIPTION .sp .LP The \fBmalloc()\fR and \fBfree()\fR functions provide a simple, general-purpose memory allocation package. The \fBmalloc()\fR function returns a pointer to a block of at least \fIsize\fR bytes suitably aligned for any use. If the space assigned by \fBmalloc()\fR is overrun, the results are undefined. .sp .LP The argument to \fBfree()\fR is a pointer to a block previously allocated by \fBmalloc()\fR, \fBcalloc()\fR, or \fBrealloc()\fR. After \fBfree()\fR is executed, this space is made available for further allocation by the application, though not returned to the system. Memory is returned to the system only upon termination of the application. If \fIptr\fR is a null pointer, no action occurs. If a random number is passed to \fBfree()\fR, the results are undefined. .sp .LP The \fBcalloc()\fR function allocates space for an array of \fInelem\fR elements of size \fIelsize\fR. The space is initialized to zeros. .sp .LP The \fBmemalign()\fR function allocates \fIsize\fR bytes on a specified alignment boundary and returns a pointer to the allocated block. The value of the returned address is guaranteed to be an even multiple of \fIalignment\fR. The value of \fIalignment\fR must be a power of two and must be greater than or equal to the size of a word. .sp .LP The \fBrealloc()\fR function changes the size of the block pointed to by \fIptr\fR to \fIsize\fR bytes and returns a pointer to the (possibly moved) block. The contents will be unchanged up to the lesser of the new and old sizes. If the new size of the block requires movement of the block, the space for the previous instantiation of the block is freed. If the new size is larger, the contents of the newly allocated portion of the block are unspecified. If size is 0, the space pointed to by \fIptr\fR is freed and a newly allocated block is returned, as if by a call to \fBmalloc(0)\fR. If \fIptr\fR is NULL, \fBrealloc()\fR behaves like \fBmalloc()\fR for the specified size. .sp .LP The \fBvalloc()\fR function has the same effect as \fBmalloc()\fR, except that the allocated memory will be aligned to a multiple of the value returned by \fBsysconf\fR(\fB_SC_PAGESIZE\fR). .sp .LP The \fBalloca()\fR function allocates \fIsize\fR bytes of space in the stack frame of the caller, and returns a pointer to the allocated block. This temporary space is automatically freed when the caller returns. If the allocated block is beyond the current stack limit, the resulting behavior is undefined. .SH RETURN VALUES .sp .LP Upon successful completion, each of the allocation functions returns a pointer to space suitably aligned (after possible pointer coercion) for storage of any type of object. .sp .LP If there is no available memory, \fBmalloc()\fR, \fBrealloc()\fR, \fBmemalign()\fR, \fBvalloc()\fR, and \fBcalloc()\fR return a null pointer. When \fBrealloc()\fR is called with \fIsize\fR > 0 and returns \fINULL\fR, the block pointed to by \fIptr\fR is left intact. If \fIsize\fR, \fInelem\fR, or \fIelsize\fR is 0, either a null pointer or a unique pointer that can be passed to \fBfree()\fR is returned. .sp .LP If \fBmalloc()\fR, \fBcalloc()\fR, or \fBrealloc()\fR returns unsuccessfully, \fBerrno\fR will be set to indicate the error. The \fBfree()\fR function does not set \fBerrno\fR. .SH ERRORS .sp .LP The \fBmalloc()\fR, \fBcalloc()\fR, and \fBrealloc()\fR functions will fail if: .sp .ne 2 .mk .na \fB\fBENOMEM\fR\fR .ad .RS 10n .rt The physical limits of the system are exceeded by \fIsize\fR bytes of memory which cannot be allocated. .RE .sp .ne 2 .mk .na \fB\fBEAGAIN\fR\fR .ad .RS 10n .rt There is not enough memory available to allocate \fIsize\fR bytes of memory; but the application could try again later. .RE .SH USAGE .sp .LP Portable applications should avoid using \fBvalloc()\fR but should instead use \fBmalloc()\fR or \fBmmap\fR(2). On systems with a large page size, the number of successful \fBvalloc()\fR operations might be 0. .sp .LP These default memory allocation routines are safe for use in multithreaded applications but are not scalable. Concurrent accesses by multiple threads are single-threaded through the use of a single lock. Multithreaded applications that make heavy use of dynamic memory allocation should be linked with allocation libraries designed for concurrent access, such as \fBlibumem\fR(3LIB) or \fBlibmtmalloc\fR(3LIB). Applications that want to avoid using heap allocations (with \fBbrk\fR(2)) can do so by using either \fBlibumem\fR(3LIB) or \fBlibmapmalloc\fR(3LIB). The allocation libraries \fBlibmalloc\fR(3LIB) and \fBlibbsdmalloc\fR(3LIB) are available for special needs. .sp .LP Comparative features of the various allocation libraries can be found in the \fBumem_alloc\fR(3MALLOC) manual page. .SH ATTRIBUTES .sp .LP See \fBattributes\fR(5) for descriptions of the following attributes: .sp .sp .TS tab() box; cw(2.75i) |cw(2.75i) lw(2.75i) |lw(2.75i) . ATTRIBUTE TYPEATTRIBUTE VALUE _ Interface StabilityCommitted _ MT-LevelSafe _ StandardSee below. .TE .sp .LP For \fBmalloc()\fR, \fBcalloc()\fR, \fBfree()\fR, \fBrealloc()\fR, and \fBvalloc()\fR, see \fBstandards\fR(5). .SH SEE ALSO .sp .LP \fBbrk\fR(2), \fBgetrlimit\fR(2), \fBlibbsdmalloc\fR(3LIB), \fBlibmalloc\fR(3LIB), \fBlibmapmalloc\fR(3LIB), \fBlibmtmalloc\fR(3LIB), \fBlibumem\fR(3LIB), \fBlibadimalloc\fR(3LIB), \fBumem_alloc\fR(3MALLOC), \fBwatchmalloc\fR(3MALLOC), \fBattributes\fR(5), \fBstandards\fR(5) .SH WARNINGS .sp .LP Undefined results will occur if the size requested for a block of memory exceeds the maximum size of a process's heap, which can be obtained with \fBgetrlimit\fR(2)