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8.1 KiB
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200 lines
8.1 KiB
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Generated
<!DOCTYPE html>
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<html>
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<head>
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<meta charset="utf-8">
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<title>Go в примерах: Указатели (Pointers)</title>
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<body>
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<div class="example" id="pointers">
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<h2><a href="./">Go в примерах</a>: Указатели (Pointers)</h2>
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<table>
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<tr>
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<td class="docs">
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<p>Go поддерживает <em><a href="http://en.wikipedia.org/wiki/Pointer_(computer_programming)">указатели</a></em>,
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позволяя вам передавать ссылки на значения и записи
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в вашей программе.</p>
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<td class="code empty leading">
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<td class="docs">
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</td>
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<td class="code leading">
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<a href="http://play.golang.org/p/VHnMkOQfQea" target="_blank"><img title="Run code" src="play.png" class="run" /></a><img title="Copy code" src="clipboard.png" class="copy" />
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<div class="highlight"><pre><span class="kn">package</span> <span class="nx">main</span>
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</pre></div>
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</td>
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<tr>
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<td class="docs">
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<td class="code leading">
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<div class="highlight"><pre><span class="kn">import</span> <span class="s">"fmt"</span>
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</pre></div>
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</td>
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</tr>
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<tr>
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<td class="docs">
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<p>Мы покажем, как работают указатели, на примере 2 функций:
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<code>zeroval</code> и <code>zeroptr</code>. В <code>zeroval</code> определен только 1
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аргумент с типом <code>int</code>, который передается по значению.
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<code>zeroval</code> получает копию <code>ival</code> при вызове функции.</p>
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</td>
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<td class="code leading">
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<div class="highlight"><pre><span class="kd">func</span> <span class="nx">zeroval</span><span class="p">(</span><span class="nx">ival</span> <span class="kt">int</span><span class="p">)</span> <span class="p">{</span>
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<span class="nx">ival</span> <span class="p">=</span> <span class="mi">0</span>
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<span class="p">}</span>
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</pre></div>
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</td>
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</tr>
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<tr>
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<td class="docs">
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<p><code>zeroptr</code> получает в качестве аргумента параметр <code>*int</code>,
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который является указателем на <code>int</code>. Запись <code>*iptr</code> в
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теле функции <em>разыменовывает</em> указатель с его адреса
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памяти на текущее значение по этому адресу. Присвоение
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значения разыменованному указателю изменяет значение
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по указанному адресу.</p>
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</td>
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<td class="code leading">
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<div class="highlight"><pre><span class="kd">func</span> <span class="nx">zeroptr</span><span class="p">(</span><span class="nx">iptr</span> <span class="o">*</span><span class="kt">int</span><span class="p">)</span> <span class="p">{</span>
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<span class="o">*</span><span class="nx">iptr</span> <span class="p">=</span> <span class="mi">0</span>
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<span class="p">}</span>
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</pre></div>
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</td>
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</tr>
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<tr>
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<td class="docs">
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</td>
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<td class="code leading">
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<div class="highlight"><pre><span class="kd">func</span> <span class="nx">main</span><span class="p">()</span> <span class="p">{</span>
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<span class="nx">i</span> <span class="o">:=</span> <span class="mi">1</span>
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<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">"initial:"</span><span class="p">,</span> <span class="nx">i</span><span class="p">)</span>
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</pre></div>
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</td>
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</tr>
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<td class="docs">
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</td>
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<td class="code leading">
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<div class="highlight"><pre> <span class="nx">zeroval</span><span class="p">(</span><span class="nx">i</span><span class="p">)</span>
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<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">"zeroval:"</span><span class="p">,</span> <span class="nx">i</span><span class="p">)</span>
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</pre></div>
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</td>
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</tr>
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<tr>
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<td class="docs">
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<p>Запись <code>&i</code> получается ссылку на область памяти, в
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которой хранится <code>i</code>, т.е. указатель на <code>i</code>.</p>
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</td>
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<td class="code leading">
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<div class="highlight"><pre> <span class="nx">zeroptr</span><span class="p">(</span><span class="o">&</span><span class="nx">i</span><span class="p">)</span>
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<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">"zeroptr:"</span><span class="p">,</span> <span class="nx">i</span><span class="p">)</span>
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</pre></div>
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</td>
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</tr>
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<tr>
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<td class="docs">
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<p>Указатели могут быть выведены на экран</p>
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</td>
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<td class="code">
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<div class="highlight"><pre> <span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">"pointer:"</span><span class="p">,</span> <span class="o">&</span><span class="nx">i</span><span class="p">)</span>
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<span class="p">}</span>
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</pre></div>
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</td>
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</tr>
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</table>
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<table>
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<tr>
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<td class="docs">
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<p><code>zeroval</code> не изменяет значение <code>i</code> в <code>main</code>, но
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<code>zeroptr</code> изменяет, т.к. в него передается указатель
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на область памяти, в которой хранится переменная.</p>
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</td>
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<td class="code">
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<div class="highlight"><pre><span class="gp">$</span> go run pointers.go
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<span class="go">initial: 1</span>
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<span class="go">zeroval: 1</span>
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<span class="go">zeroptr: 0</span>
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<span class="go">pointer: 0x42131100</span>
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</pre></div>
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</td>
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</tr>
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</table>
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<p class="next">
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Следующий пример: <a href="structs">Структуры (Structs)</a>.
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</p>
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<p class="footer">
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by <a href="https://markmcgranaghan.com">Mark McGranaghan</a> | <a href="https://github.com/mmcgrana/gobyexample/blob/master/examples/pointers">source</a> | <a href="https://github.com/mmcgrana/gobyexample#license">license</a>
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</p>
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</div>
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<script>
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var codeLines = [];
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codeLines.push('');codeLines.push('package main\u000A');codeLines.push('import \"fmt\"\u000A');codeLines.push('func zeroval(ival int) {\u000A ival = 0\u000A}\u000A');codeLines.push('func zeroptr(iptr *int) {\u000A *iptr = 0\u000A}\u000A');codeLines.push('func main() {\u000A i := 1\u000A fmt.Println(\"initial:\", i)\u000A');codeLines.push(' zeroval(i)\u000A fmt.Println(\"zeroval:\", i)\u000A');codeLines.push(' zeroptr(&i)\u000A fmt.Println(\"zeroptr:\", i)\u000A');codeLines.push(' fmt.Println(\"pointer:\", &i)\u000A}\u000A');codeLines.push('');
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</script>
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