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chromium / external / gitster / git-htmldocs / ec3b9a7c740602964acf4b5a31612500c3aefb74 / . / technical / api-allocation-growing.html
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Junio C Hamano3dac5042007-12-15 08:40:54[diff] [blame]305</style>
306<title>allocation growing API</title>
307</head>
308<body>
309<div id="header">
310<h1>allocation growing API</h1>
311</div>
312<div id="preamble">
313<div class="sectionbody">
Junio C Hamano4604fe52008-09-19 06:37:10[diff] [blame]314<div class="para"><p>Dynamically growing an array using realloc() is error prone and boring.</p></div>
315<div class="para"><p>Define your array with:</p></div>
316<div class="ilist"><ul>
Junio C Hamano3dac5042007-12-15 08:40:54[diff] [blame]317<li>
318<p>
319a pointer (<tt>ary</tt>) that points at the array, initialized to <tt>NULL</tt>;
320</p>
321</li>
322<li>
323<p>
324an integer variable (<tt>alloc</tt>) that keeps track of how big the current
325 allocation is, initialized to <tt>0</tt>;
326</p>
327</li>
328<li>
329<p>
330another integer variable (<tt>nr</tt>) to keep track of how many elements the
331 array currently has, initialized to <tt>0</tt>.
332</p>
333</li>
Junio C Hamano4604fe52008-09-19 06:37:10[diff] [blame]334</ul></div>
335<div class="para"><p>Then before adding <tt>n`th element to the array, call `ALLOC_GROW(ary, n,
Junio C Hamano3dac5042007-12-15 08:40:54[diff] [blame]336alloc)</tt>. This ensures that the array can hold at least <tt>n</tt> elements by
Junio C Hamano4604fe52008-09-19 06:37:10[diff] [blame]337calling <tt>realloc(3)</tt> and adjusting <tt>alloc</tt> variable.</p></div>
Junio C Hamano3dac5042007-12-15 08:40:54[diff] [blame]338<div class="listingblock">
339<div class="content">
340<pre><tt>sometype *ary;
341size_t nr;
342size_t alloc
343
344for (i = 0; i &lt; nr; i++)
345 if (we like ary[i] already)
346 return;
347
348/* we did not like any existing one, so add one */
349ALLOC_GROW(ary, nr + 1, alloc);
350ary[nr++] = value you like;</tt></pre>
351</div></div>
Junio C Hamano4604fe52008-09-19 06:37:10[diff] [blame]352<div class="para"><p>You are responsible for updating the <tt>nr</tt> variable.</p></div>
Junio C Hamano3dac5042007-12-15 08:40:54[diff] [blame]353</div>
354</div>
355<div id="footer">
356<div id="footer-text">
Junio C Hamanoec87f522008-12-10 08:35:25[diff] [blame]357Last updated 2008-12-10 08:33:36 UTC
Junio C Hamano3dac5042007-12-15 08:40:54[diff] [blame]358</div>
359</div>
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361</html>