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POSIX_MEMALIGN(3) Linux Programmer's Manual POSIX_MEMALIGN(3) NAME posix_memalign, memalign, valloc - Allocate aligned memory SYNOPSIS #include <stdlib.h> int posix_memalign(void **memptr, size_t alignment, size_t size); void *memalign(size_t boundary, size_t size); void *valloc(size_t size); DESCRIPTION The function posix_memalign() allocates size bytes and places the ad- dress of the allocated memory in *memptr. The address of the allocated memory will be a multiple of alignment, which must be a power of two and a multiple of sizeof(void *). The obsolete function memalign() allocates size bytes and returns a pointer to the allocated memory. The memory address will be a multiple of boundary, which must be a power of two. The obsolete function valloc() allocates size bytes and returns a pointer to the allocated memory. The memory address will be a multiple of the page size. It is equivalent to memalign(sysconf(_SC_PAGE- SIZE),size). For all three routines, the memory is not zeroed. RETURN VALUE memalign() and valloc() return the pointer to the allocated memory, or NULL if the request fails. posix_memalign() returns zero on success, or one of the error values listed in the next section on failure. Note that errno is not set. ERRORS EINVAL The alignment parameter was not a power of two, or was not a multiple of sizeof(void *). ENOMEM There was insufficient memory to fulfill the allocation request. NOTES posix_memalign() verifies that alignment matches the requirements de- tailed above. memalign() may not check that the boundary parameter is correct. POSIX requires that memory obtained from posix_memalign() can be freed using free(). Some systems provide no way to reclaim memory allocated with memalign() or valloc() (because one can only pass to free() a pointer gotten from malloc(), while e.g. memalign() would call mal- loc() and then align the obtained value). GNU libc allows memory ob- tained from any of these three routines to be reclaimed with free(). GNU libc malloc() always returns 8-byte aligned memory addresses, so these routines are only needed if you require larger alignment values. AVAILABILITY The functions memalign() and valloc() have been available in all Linux libc libraries. The function posix_memalign() is available since glibc 2.1.91. CONFORMING TO The function valloc() appeared in 3.0 BSD. It is documented as being obsolete in BSD 4.3, and as legacy in SUSv2. It no longer occurs in SUSv3. The function memalign() appears in SunOS 4.1.3 but not in BSD 4.4. The function posix_memalign() comes from POSIX 1003.1d. SEE ALSO malloc(3), free(3), getpagesize(2), brk(2) GNU 2001-10-11 POSIX_MEMALIGN(3)
NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | NOTES | AVAILABILITY | CONFORMING TO | SEE ALSO
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