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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.
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 obstackobject 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_allocfunction if it needs to allocate a new chunk of memory; it callsobstack_alloc_failed_handlerif allocation of memory byobstack_chunk_allocfailed.
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:
This allocates a block and initializes it by copying size bytes of data starting at address. It calls
obstack_alloc_failed_handlerif allocation of memory byobstack_chunk_allocfailed.
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 (see Basic Allocation).