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(libc.info)Allocation in an Obstack

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Allocation in an Obstack
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   The most direct way to allocate an object in an obstack is with
`obstack_alloc', which is invoked almost like `malloc'.

 - Function: void * obstack_alloc (struct obstack *OBSTACK-PTR, int
          SIZE)
     This allocates an uninitialized block of SIZE bytes in an obstack
     and returns its address.  Here OBSTACK-PTR specifies which obstack
     to allocate the block in; it is the address of the `struct obstack'
     object which represents the obstack.  Each obstack function or
     macro requires you to specify an OBSTACK-PTR as the first argument.

     This function calls the obstack's `obstack_chunk_alloc' function if
     it needs to allocate a new chunk of memory; it calls
     `obstack_alloc_failed_handler' if allocation of memory by
     `obstack_chunk_alloc' failed.

   For example, here is a function that allocates a copy of a string STR
in a specific obstack, which is in the variable `string_obstack':

     struct obstack string_obstack;
     
     char *
     copystring (char *string)
     {
       size_t len = strlen (string) + 1;
       char *s = (char *) obstack_alloc (&string_obstack, len);
       memcpy (s, string, len);
       return s;
     }

   To allocate a block with specified contents, use the function
`obstack_copy', declared like this:

 - Function: void * obstack_copy (struct obstack *OBSTACK-PTR, void
          *ADDRESS, int SIZE)
     This allocates a block and initializes it by copying SIZE bytes of
     data starting at ADDRESS.  It calls `obstack_alloc_failed_handler'
     if allocation of memory by `obstack_chunk_alloc' failed.

 - Function: void * obstack_copy0 (struct obstack *OBSTACK-PTR, void
          *ADDRESS, int SIZE)
     Like `obstack_copy', but appends an extra byte containing a null
     character.  This extra byte is not counted in the argument SIZE.

   The `obstack_copy0' function is convenient for copying a sequence of
characters into an obstack as a null-terminated string.  Here is an
example of its use:

     char *
     obstack_savestring (char *addr, int size)
     {
       return obstack_copy0 (&myobstack, addr, size);
     }

Contrast this with the previous example of `savestring' using `malloc'
(Note: Basic Allocation).