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malloc(3c)

Name
     malloc, calloc, free, memalign, realloc,  valloc,  alloca  -
     memory allocator

Synopsis
     #include <stdlib.h>

     void *malloc(size_t size);


     void *calloc(size_t nelem, size_t elsize);


     void free(void *ptr);


     void *memalign(size_t alignment, size_t size);


     void *realloc(void *ptr, size_t size);


     void *valloc(size_t size);


     #include <alloca.h>

     void *alloca(size_t size);

Description
     The  malloc()  and  free()  functions  provide   a   simple,
     general-purpose  memory  allocation  package.  The  malloc()
     function returns a pointer to a block of at least size bytes
     suitably  aligned for any use. If the space assigned by mal-
     loc() is overrun, the results are undefined.


     The argument to free() is a pointer to  a  block  previously
     allocated  by malloc(), calloc(), or realloc(). After free()
     is executed, this space is made available for further  allo-
     cation  by  the application, though not returned to the sys-
     tem. Memory is returned to the system only upon  termination
     of  the  application.  If   ptr is a null pointer, no action
     occurs. If a random number is passed to free(), the  results
     are undefined.


     The calloc() function allocates space for an array of  nelem
     elements of size elsize. The space is initialized to zeros.

     The memalign() function allocates size 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 alignment. The value of alignment must
     be a power of two and must be greater than or equal  to  the
     size of a word.


     The realloc() function changes the size of the block pointed
     to by ptr to size bytes and returns a pointer to the (possi-
     bly 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 pre-
     vious  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 ptr is freed and a newly allocated block is  returned,
     as  if  by  a  call  to malloc(0). If ptr is NULL, realloc()
     behaves like malloc() for the specified size.


     The valloc() function  has  the  same  effect  as  malloc(),
     except that the allocated memory will be aligned to a multi-
     ple of the value returned by sysconf(_SC_PAGESIZE).


     The alloca() function allocates size 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  unde-
     fined.

Return Values
     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.


     If  there  is  no  available  memory,  malloc(),  realloc(),
     memalign(),  valloc(),  and  calloc() return a null pointer.
     When realloc() is called with size > 0 and returns NULL, the
     block  pointed  to by ptr is left intact. If size, nelem, or
     elsize is 0, either a null pointer or a unique pointer  that
     can be passed to free() is returned.


     If malloc(), calloc(), or realloc() returns  unsuccessfully,
     errno will be set to indicate the error. The free() function
     does not set errno.

Errors
     The malloc(), calloc(), and realloc()  functions  will  fail
     if:

     ENOMEM
               The physical limits of the system are exceeded  by
               size bytes of memory which cannot be allocated.


     EAGAIN
               There is not enough memory available  to  allocate
               size  bytes  of  memory; but the application could
               try again later.

Usage
     Portable applications should avoid using valloc() but should
     instead  use  malloc()  or  mmap(2). On systems with a large
     page size, the  number  of  successful  valloc()  operations
     might be 0.


     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
     libumem(3LIB) or libmtmalloc(3LIB). Applications  that  want
     to  avoid  using heap allocations (with brk(2)) can do so by
     using either libumem(3LIB) or libmapmalloc(3LIB). The  allo-
     cation  libraries libmalloc(3LIB) and libbsdmalloc(3LIB) are
     available for special needs.


     Comparative features of the various allocation libraries can
     be found in the umem_alloc(3MALLOC) manual page.

Attributes
     See attributes(5) for descriptions of the  following  attri-
     butes:



     tab() box; cw(2.75i) |cw(2.75i) lw(2.75i) |lw(2.75i)  ATTRI-
     BUTE  TYPEATTRIBUTE  VALUE  _ Interface StabilityCommitted _
     MT-LevelSafe _ StandardSee below.



     For malloc(), calloc(), free(), realloc(), and valloc(), see
     standards(5).

See Also
     brk(2), getrlimit(2),  libbsdmalloc(3LIB),  libmalloc(3LIB),
     libmapmalloc(3LIB),     libmtmalloc(3LIB),    libumem(3LIB),
     libadimalloc(3LIB),                     umem_alloc(3MALLOC),
     watchmalloc(3MALLOC), attributes(5), standards(5)

Warnings
     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 getrlimit(2)
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