4.3BSD - /usr/man/cat3/alloca.0

MALLOC(3)                                                            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, allo‐
       cating  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.

       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 mem‐
       ory 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.


4th Berkeley Distribution        May 14, 1986                        MALLOC(3)