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MALLOC(3)                  Library Functions 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  simple 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.

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 stor-
       ing 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.

       Alloca is machine dependent; it's use is discouraged.



4th Berkeley Distribution       19 January 1983                      MALLOC(3)