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| <h5 class="subsubsection">3.2.4.1 Creating Obstacks</h5> |
| |
| <p>The utilities for manipulating obstacks are declared in the header |
| file <samp><span class="file">obstack.h</span></samp>. |
| <a name="index-obstack_002eh-301"></a> |
| <!-- obstack.h --> |
| <!-- GNU --> |
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| <div class="defun"> |
| — Data Type: <b>struct obstack</b><var><a name="index-struct-obstack-302"></a></var><br> |
| <blockquote><p>An obstack is represented by a data structure of type <code>struct |
| obstack</code>. This structure has a small fixed size; it records the status |
| of the obstack and how to find the space in which objects are allocated. |
| It does not contain any of the objects themselves. You should not try |
| to access the contents of the structure directly; use only the functions |
| described in this chapter. |
| </p></blockquote></div> |
| |
| <p>You can declare variables of type <code>struct obstack</code> and use them as |
| obstacks, or you can allocate obstacks dynamically like any other kind |
| of object. Dynamic allocation of obstacks allows your program to have a |
| variable number of different stacks. (You can even allocate an |
| obstack structure in another obstack, but this is rarely useful.) |
| |
| <p>All the functions that work with obstacks require you to specify which |
| obstack to use. You do this with a pointer of type <code>struct obstack |
| *</code>. In the following, we often say “an obstack” when strictly |
| speaking the object at hand is such a pointer. |
| |
| <p>The objects in the obstack are packed into large blocks called |
| <dfn>chunks</dfn>. The <code>struct obstack</code> structure points to a chain of |
| the chunks currently in use. |
| |
| <p>The obstack library obtains a new chunk whenever you allocate an object |
| that won't fit in the previous chunk. Since the obstack library manages |
| chunks automatically, you don't need to pay much attention to them, but |
| you do need to supply a function which the obstack library should use to |
| get a chunk. Usually you supply a function which uses <code>malloc</code> |
| directly or indirectly. You must also supply a function to free a chunk. |
| These matters are described in the following section. |
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