MALLOC(3C)           INTERACTIVE UNIX System           MALLOC(3C)



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

          SYNOPSIS
               char *malloc (size)
               unsigned size;

               void free (ptr)
               char *ptr;

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

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

          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.

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

               Undefined results will occur if the space assigned by malloc
               is overrun or if some random number is handed to free.

               The malloc function allocates the first big enough, contigu-
               ous reach of free space found in a circular search from the
               last block allocated or freed, coalescing adjacent free
               blocks as it searches.  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.  If no free block of size bytes is
               available in the storage arena, then realloc will ask malloc
               to enlarge the arena by size bytes and will then move the
               data to the new space.

               Realloc also works if ptr points to a block freed since the
               last call of malloc, realloc, or calloc; thus sequences of
               free, malloc, and realloc can exploit the search strategy of
               malloc to do storage compaction.

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


          Rev. C Software Development Set                            Page 1

          MALLOC(3C)           INTERACTIVE UNIX System           MALLOC(3C)



               Each of the allocation routines returns a pointer to space
               suitably aligned (after possible pointer coercion) for
               storage of any type of object.

          SEE ALSO
               brk(2), malloc(3X).

          DIAGNOSTICS
               The malloc, realloc and calloc functions return a NULL
               pointer if there is no available memory, or if the arena has
               been detectably corrupted by storing outside the bounds of a
               block.  When this happens the block pointed to by ptr may be
               destroyed.

          NOTES
               Search time increases when many objects have been allocated;
               that is, if a program allocates but never frees, then each
               successive allocation takes longer.  For an alternate, more
               flexible implementation, see malloc(3X).




































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