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    <p>The rule is correct. However, one should be very careful in applying it.</p> <p>I suggest to apply it in a more formal way for C99+ declarations.</p> <p>The most important thing here is to recognize the following recursive structure of all declarations (<code>const</code>, <code>volatile</code>, <code>static</code>, <code>extern</code>, <code>inline</code>, <code>struct</code>, <code>union</code>, <code>typedef</code> are removed from the picture for simplicity but can be added back easily):</p> <pre><code>base-type [derived-part1: *'s] [object] [derived-part2: []'s or ()] </code></pre> <p>Yep, that's it, four parts.</p> <pre><code>where base-type is one of the following (I'm using a bit compressed notation): void [signed/unsigned] char [signed/unsigned] short [int] signed/unsigned [int] [signed/unsigned] long [long] [int] float [long] double etc object is an identifier OR ([derived-part1: *'s] [object] [derived-part2: []'s or ()]) * is *, denotes a reference/pointer and can be repeated [] in derived-part2 denotes bracketed array dimensions and can be repeated () in derived-part2 denotes parenthesized function parameters delimited with ,'s [] elsewhere denotes an optional part () elsewhere denotes parentheses </code></pre> <p>Once you've got all 4 parts parsed,</p> <p>&nbsp;&nbsp;[<code>object</code>] is [<code>derived-part2</code> (containing/returning)] [<code>derived-part2</code> (pointer to)] <code>base-type</code> <sup>1</sup>.</p> <p>If there's recursion, you find your <code>object</code> (if there's any) at the bottom of the recursion stack, it'll be the inner-most one and you'll get the full declaration by going back up and collecting and combining derived parts at each level of recursion.</p> <p>While parsing you may move <code>[object]</code> to after <code>[derived-part2]</code> (if any). This will give you a linearized, easy to understand, declaration (see <sup>1</sup> above).</p> <p>Thus, in</p> <pre><code>char* (**(*foo[3][5])(void))[7][9]; </code></pre> <p>you get:</p> <ol> <li><code>base-type</code> = <code>char</code></li> <li>level 1: <code>derived-part1</code> = <code>*</code>, <code>object</code> = <code>(**(*foo[3][5])(void))</code>, <code>derived-part2</code> = <code>[7][9]</code></li> <li>level 2: <code>derived-part1</code> = <code>**</code>, <code>object</code> = <code>(*foo[3][5])</code>, <code>derived-part2</code> = <code>(void)</code></li> <li>level 3: <code>derived-part1</code> = <code>*</code>, <code>object</code> = <code>foo</code>, <code>derived-part2</code> = <code>[3][5]</code></li> </ol> <p>From there:</p> <ol> <li>level 3: <code>*</code> <code>[3][5]</code> <code>foo</code></li> <li>level 2: <code>**</code> <code>(void)</code> <code>*</code> <code>[3][5]</code> <code>foo</code></li> <li>level 1: <code>*</code> <code>[7][9]</code> <code>**</code> <code>(void)</code> <code>*</code> <code>[3][5]</code> <code>foo</code></li> <li>finally, <code>char</code> <code>*</code> <code>[7][9]</code> <code>**</code> <code>(void)</code> <code>*</code> <code>[3][5]</code> <code>foo</code></li> </ol> <p>Now, reading right to left:</p> <p><code>foo</code> is an array of 3 arrays of 5 pointers to a function (taking no params) returning a pointer to a pointer to an array of 7 arrays of 9 pointers to a char.</p> <p>You could reverse the array dimensions in every <code>derived-part2</code> in the process as well.</p> <p>That's your spiral rule.</p> <p>And it's easy to see the spiral. You dive into the ever more deeply nested <code>[object]</code> from the left and then resurface on the right only to note that on the upper level there's another pair of left and right and so on.</p>
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    1. POThe spiral rule about declarations — when is it in error?
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    1. USAlexey Frunze
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    1. COInteresting. First you say that the rule is correct, then you give an explication of how to read a declaration which doesn't use it, and in fact contradicts it.
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    2. COYou might mention that when you recurse (I'd use the term nest, but it comes down to the same thing), nested parts of the declaration don't contain your `base-part` (except in function parameters, where you have a complete declaration nested in another declaration).
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    3. CO@JamesKanze That which you want to mention should be immediately apparent. Observe that there's no `base-type` anywhere under `object is...`.
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