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<h1><a href="./">C*</a></h1>
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<h1 id="pointers">Pointers</h1>
<p>Pointers, written <code>T*</code> (where <code>T</code> is the pointed-to type), are used to refer to other objects in memory.</p>
<p>C* pointers are mostly like C/C++ pointers, with the following differences: - They cannot be null by default. To create nullable pointers, they need to be marked as <a href="nullable-types">nullable</a>. - They don’t support pointer arithmetic. For pointer arithmetic, array pointers have to be used, see below. - When passing a <code>T*</code> where a <code>T</code> is expected, the pointer is automatically dereferenced. - When passing a <code>T</code> value where a <code>T*</code> is expected, the address is automatically passed.</p>
<p>To form a pointer, the <code>&</code> operator can be used. To dereference a pointer, the <code>*</code> operator can be used. Comparing pointers compares the stored memory addresses. To compare the pointed values, the pointers need to be dereferenced first.</p>
<div class="sourceCode" id="cb1"><pre class="sourceCode cs"><code class="sourceCode cs"><span id="cb1-1"><a href="#cb1-1" aria-hidden="true" tabindex="-1"></a><span class="dt">void</span> <span class="fu">main</span><span class="op">()</span> <span class="op">{</span></span>
<span id="cb1-2"><a href="#cb1-2" aria-hidden="true" tabindex="-1"></a> <span class="dt">int</span> i <span class="op">=</span> <span class="dv">6</span><span class="op">;</span></span>
<span id="cb1-3"><a href="#cb1-3" aria-hidden="true" tabindex="-1"></a> <span class="dt">int</span><span class="op">*</span> p <span class="op">=</span> <span class="op">&</span>i<span class="op">;</span> <span class="co">// Make p point to i</span></span>
<span id="cb1-4"><a href="#cb1-4" aria-hidden="true" tabindex="-1"></a> <span class="fu">println</span><span class="op">(</span>p<span class="op">);</span> <span class="co">// Prints 6</span></span>
<span id="cb1-5"><a href="#cb1-5" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb1-6"><a href="#cb1-6" aria-hidden="true" tabindex="-1"></a> <span class="dt">int</span><span class="op">*</span> q <span class="op">=</span> p<span class="op">;</span> <span class="co">// Copy p to q, both point to i now</span></span>
<span id="cb1-7"><a href="#cb1-7" aria-hidden="true" tabindex="-1"></a> <span class="fu">println</span><span class="op">(</span>p <span class="op">==</span> q<span class="op">);</span> <span class="co">// Prints true because both pointers point to the same memory address</span></span>
<span id="cb1-8"><a href="#cb1-8" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb1-9"><a href="#cb1-9" aria-hidden="true" tabindex="-1"></a> <span class="dt">int</span> j <span class="op">=</span> <span class="dv">6</span><span class="op">;</span></span>
<span id="cb1-10"><a href="#cb1-10" aria-hidden="true" tabindex="-1"></a> p <span class="op">=</span> <span class="op">&</span>j<span class="op">;</span> <span class="co">// Change p to point to j</span></span>
<span id="cb1-11"><a href="#cb1-11" aria-hidden="true" tabindex="-1"></a> <span class="fu">println</span><span class="op">(</span>p <span class="op">==</span> q<span class="op">);</span> <span class="co">// Prints false because pointers point to different memory addresses</span></span>
<span id="cb1-12"><a href="#cb1-12" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb1-13"><a href="#cb1-13" aria-hidden="true" tabindex="-1"></a> <span class="op">*</span>p <span class="op">=</span> <span class="dv">7</span><span class="op">;</span> <span class="co">// Change the value of j</span></span>
<span id="cb1-14"><a href="#cb1-14" aria-hidden="true" tabindex="-1"></a> <span class="fu">println</span><span class="op">(*</span>p <span class="op">+</span> <span class="op">*</span>q<span class="op">);</span> <span class="co">// Sums the values pointed to by p and q, prints 13</span></span>
<span id="cb1-15"><a href="#cb1-15" aria-hidden="true" tabindex="-1"></a><span class="op">}</span></span></code></pre></div>
<h2 id="array-pointers">Array pointers</h2>
<p>Array pointers, written <code>T[*]</code>, are pointers that point to an array of unknown length, or one step past the end of an array. They are the only pointer type that supports pointer arithmetic, since pointer arithmetic only makes sense for arrays.</p>
<div class="sourceCode" id="cb2"><pre class="sourceCode cs"><code class="sourceCode cs"><span id="cb2-1"><a href="#cb2-1" aria-hidden="true" tabindex="-1"></a><span class="dt">void</span> <span class="fu">main</span><span class="op">()</span> <span class="op">{</span></span>
<span id="cb2-2"><a href="#cb2-2" aria-hidden="true" tabindex="-1"></a> <span class="dt">int</span><span class="op">[</span><span class="dv">3</span><span class="op">]</span> a <span class="op">=</span> <span class="op">[</span><span class="dv">1</span><span class="op">,</span> <span class="dv">2</span><span class="op">,</span> <span class="dv">3</span><span class="op">];</span></span>
<span id="cb2-3"><a href="#cb2-3" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb2-4"><a href="#cb2-4" aria-hidden="true" tabindex="-1"></a> <span class="dt">int</span><span class="op">[*]</span> p <span class="op">=</span> a<span class="op">;</span> <span class="co">// p points to a</span></span>
<span id="cb2-5"><a href="#cb2-5" aria-hidden="true" tabindex="-1"></a> <span class="fu">println</span><span class="op">(</span>p<span class="op">[</span><span class="dv">0</span><span class="op">]);</span> <span class="co">// prints 1</span></span>
<span id="cb2-6"><a href="#cb2-6" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb2-7"><a href="#cb2-7" aria-hidden="true" tabindex="-1"></a> p<span class="op">++;</span> <span class="co">// increment pointer to next element</span></span>
<span id="cb2-8"><a href="#cb2-8" aria-hidden="true" tabindex="-1"></a> <span class="fu">println</span><span class="op">(</span>p<span class="op">[</span><span class="dv">0</span><span class="op">]);</span> <span class="co">// prints 2</span></span>
<span id="cb2-9"><a href="#cb2-9" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb2-10"><a href="#cb2-10" aria-hidden="true" tabindex="-1"></a> p <span class="op">=</span> <span class="op">&</span>p<span class="op">[</span><span class="dv">1</span><span class="op">];</span> <span class="co">// increment pointer to next element</span></span>
<span id="cb2-11"><a href="#cb2-11" aria-hidden="true" tabindex="-1"></a> <span class="fu">println</span><span class="op">(*</span>p<span class="op">);</span> <span class="co">// *p is equivalent to p[0], prints 3</span></span>
<span id="cb2-12"><a href="#cb2-12" aria-hidden="true" tabindex="-1"></a><span class="op">}</span></span></code></pre></div>
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