MALLOC(3)	    UNIX Programmer's Manual		MALLOC(3)


NAME
     malloc, free, realloc, calloc, alloca - memory allocator

SYNOPSIS
     char *malloc(size)
     unsigned size;

     free(ptr)
     char *ptr;

     char *realloc(ptr, size)
     char *ptr;
     unsigned size;

     char *calloc(nelem, elsize)
     unsigned nelem, elsize;

     char *alloca(size)
     int size;

DESCRIPTION
     Malloc and free provide a general-purpose memory allocation
     package.  Malloc returns a pointer to a block of at least
     size bytes beginning on a word boundary.

     The argument to free is a pointer to a block previously
     allocated by malloc; this space is made available for
     further allocation, but its contents are left undisturbed.

     Needless to say, grave disorder will result if the space
     assigned by malloc is overrun or if some random number is
     handed to free.

     Malloc maintains multiple lists of free blocks according to
     size, allocating space from the appropriate list.	It calls
     sbrk (see brk(2)) to get more memory from the system when
     there is no suitable space already free.

     Realloc changes the size of the block pointed to by ptr to
     size 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.

     In order to be compatible with older versions, realloc also
     works if ptr points to a block freed since the last call of
     malloc, realloc or calloc; sequences of free, malloc and
     realloc were previously used to attempt storage compaction.
     This procedure is no longer recommended.

     Calloc allocates space for an array of nelem elements of
     size elsize. The space is initialized to zeros.


Printed 11/26/99	  May 14, 1986				1


MALLOC(3)	    UNIX Programmer's Manual		MALLOC(3)


     Alloca allocates size bytes of space in the stack frame of
     the caller.  This temporary space is automatically freed on
     return.

     Each of the allocation routines returns a pointer to space
     suitably aligned (after possible pointer coercion) for
     storage of any type of object.  If the space is of pagesize
     or larger, the memory returned will be page-aligned.

SEE ALSO
     brk(2), pagesize(2)

DIAGNOSTICS
     Malloc, realloc and calloc return a null pointer (0) if
     there is no available memory or if the arena has been
     detectably corrupted by storing outside the bounds of a
     block.  Malloc may be recompiled to check the arena very
     stringently on every transaction; those sites with a source
     code license may check the source code to see how this can
     be done.

BUGS
     When realloc returns 0, the block pointed to by ptr may be
     destroyed.

     The current implementation of malloc does not always fail
     gracefully when system memory limits are approached.  It may
     fail to allocate memory when larger free blocks could be
     broken up, or when limits are exceeded because the size is
     rounded up.  It is optimized for sizes that are powers of
     two.

     Alloca is machine dependent; its use is discouraged.


Printed 11/26/99	  May 14, 1986				2


 
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