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349 lines
12 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<head>
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<meta http-equiv="content-type" content="text/html; charset=UTF-8">
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<title>将数据打包成二进制字符串</title>
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</head>
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<body class="docs"><div id="layout">
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<div id="layout-content"><div id="function.pack" class="refentry">
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<div class="refnamediv">
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<h1 class="refname">pack</h1>
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<p class="verinfo">(PHP 4, PHP 5, PHP 7)</p><p class="refpurpose"><span class="refname">pack</span> — <span class="dc-title">将数据打包成二进制字符串</span></p>
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</div>
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<div class="refsect1 description" id="refsect1-function.pack-description">
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<h3 class="title">说明</h3>
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<div class="methodsynopsis dc-description">
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<span class="methodname"><strong>pack</strong></span>
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( <span class="methodparam"><span class="type">string</span> <code class="parameter">$format</code></span>
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[, <span class="methodparam"><span class="type"><a href="language.pseudo-types.html#language.types.mixed" class="type mixed">mixed</a></span> <code class="parameter">$args</code></span>
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[, <span class="methodparam"><span class="type"><a href="language.pseudo-types.html#language.types.mixed" class="type mixed">mixed</a></span> <code class="parameter">$...</code></span>
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]] ) : <span class="type">string</span></div>
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<p class="para rdfs-comment">
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根据<code class="parameter">format</code>将给地的参数打包成二进制字符串。
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</p>
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<p class="para">
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这个函数的思想来自Perl，所有格式化代码（<code class="parameter">format</code>）的工作原理都与Perl相同。 但是，缺少了部分格式代码，比如Perl的“u”。
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</p>
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<p class="para">
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注意，有符号值和无符号值之间的区别只影响函数<span class="function"><a href="unpack.html" class="function">unpack()</a></span>, 在那些使用有符号和无符号格式代码的地方<span class="function"><strong>pack()</strong></span>函数产生相同的结果。
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</p>
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</div>
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<div class="refsect1 parameters" id="refsect1-function.pack-parameters">
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<h3 class="title">参数</h3>
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<p class="para">
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<dl>
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<dt>
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<code class="parameter">format</code></dt>
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<dd>
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<p class="para">
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<code class="parameter">format</code>字符串由格式代码组成，后面跟着一个可选的重复参数。 重复参数可以是一个整数值或者<em>*</em>值来重复到输入数据的末尾。对于a, A, h, H格式化代码，其后的重复参数指定了给定数据将会被使用几个字符串，对于@,其后的数字表示放置剩余数据的绝对定位（之前的数据将会被空字符串填充），对于其他所有内容，重复数量指定消耗多少数据并将其打包到生成的二进制字符串中。
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</p>
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<p class="para">
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目前已实现的格式如下：
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<table class="doctable table">
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<caption><strong><span class="function"><strong>pack()</strong></span> 格式字符</strong></caption>
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<thead>
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<tr>
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<th>代码</th>
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<th>描述</th>
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</tr>
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</thead>
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<tbody class="tbody">
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<tr>
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<td>a</td>
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<td>以NUL字节填充字符串</td>
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</tr>
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<tr>
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<td>A</td>
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<td>以SPACE(空格)填充字符串</td></tr>
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<tr>
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<td>h</td>
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<td>十六进制字符串，低位在前</td></tr>
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<tr>
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<td>H</td>
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<td>十六进制字符串，高位在前</td></tr>
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<tr><td>c</td><td>有符号字符</td></tr>
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<tr>
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<td>C</td>
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<td>无符号字符</td></tr>
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<tr>
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<td>s</td>
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<td>有符号短整型(16位，主机字节序)</td>
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</tr>
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<tr>
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<td>S</td>
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<td>无符号短整型(16位，主机字节序)</td>
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</tr>
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<tr>
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<td>n</td>
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<td>无符号短整型(16位，大端字节序)</td>
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</tr>
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<tr>
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<td>v</td>
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<td>无符号短整型(16位，小端字节序)</td>
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</tr>
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<tr>
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<td>i</td>
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<td>有符号整型(机器相关大小字节序)</td>
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</tr>
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<tr>
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<td>I</td>
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<td>无符号整型(机器相关大小字节序)</td>
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</tr>
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<tr>
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<td>l</td>
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<td>有符号长整型(32位，主机字节序)</td>
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</tr>
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<tr>
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<td>L</td>
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<td>无符号长整型(32位，主机字节序)</td>
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</tr>
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<tr>
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<td>N</td>
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<td>无符号长整型(32位，大端字节序)</td>
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</tr>
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<tr>
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<td>V</td>
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<td>无符号长整型(32位，小端字节序)</td>
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</tr>
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<tr>
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<td>q</td>
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<td>有符号长长整型(64位，主机字节序)</td>
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</tr>
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<tr>
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<td>Q</td>
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<td>无符号长长整型(64位，主机字节序)</td>
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</tr>
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<tr>
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<td>J</td>
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<td>无符号长长整型(64位，大端字节序)</td>
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</tr>
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<tr>
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<td>P</td>
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<td>无符号长长整型(64位，小端字节序)</td>
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</tr>
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<tr>
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<td>f</td>
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<td>单精度浮点型(机器相关大小)</td>
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</tr>
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<tr>
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<td>g</td>
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<td>单精度浮点型(机器相关大小，小端字节序)</td>
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</tr>
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<tr>
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<td>G</td>
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<td>单精度浮点型(机器相关大小，大端字节序)</td>
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</tr>
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<tr>
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<td>d</td>
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<td>双精度浮点型(机器相关大小)</td>
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</tr>
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<tr>
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<td>e</td>
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<td>双精度浮点型(机器相关大小，小端字节序)</td>
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</tr>
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<tr>
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<td>E</td>
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<td>双精度浮点型(机器相关大小，大端字节序)</td>
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</tr>
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<tr>
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<td>x</td>
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<td>NUL字节</td>
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</tr>
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<tr>
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<td>X</td>
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<td>回退已字节</td>
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</tr>
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<tr>
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<td>Z</td>
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<td>以NUL字节填充字符串空白(PHP 5.5中新加入的)</td>
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</tr>
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<tr>
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<td>@</td>
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<td>NUL填充到绝对位置</td>
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</tr>
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</tbody>
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</table>
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</p>
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</dd>
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<dt>
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<code class="parameter">args</code></dt>
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<dd>
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<p class="para">
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</p>
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</dd>
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</dl>
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</p>
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</div>
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<div class="refsect1 returnvalues" id="refsect1-function.pack-returnvalues">
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<h3 class="title">返回值</h3>
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<p class="para">
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返回包含数据的二进制字符串。
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</p>
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</div>
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<div class="refsect1 changelog" id="refsect1-function.pack-changelog">
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<h3 class="title">更新日志</h3>
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<p class="para">
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<table class="doctable informaltable">
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<thead>
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<tr>
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<th>版本</th>
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<th>说明</th>
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</tr>
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</thead>
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<tbody class="tbody">
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<tr>
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<td>7.2.0</td>
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<td>
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<span class="type"><a href="language.types.float.html" class="type float">float</a></span> 和 <span class="type"><a href="language.types.float.html" class="type double">double</a></span> 类型支持打断和小端。
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</td>
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</tr>
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<tr>
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<td>7.0.15,7.1.1</td>
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<td>
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添加了"e","E","g"和"G"代码以启用float和double的字节顺序支持。
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</td>
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</tr>
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<tr>
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<td>5.6.3</td>
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<td>
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添加了“q”、“q”、“J”和“P”代码以支持处理64位数字。
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</td>
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</tr>
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<tr>
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<td>5.5.0</td>
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<td>
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“Z”代码添加了与“a”等效的功能，以实现Perl兼容性。
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</td>
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</tr>
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</tbody>
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</table>
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</p>
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</div>
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<div class="refsect1 examples" id="refsect1-function.pack-examples">
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<h3 class="title">范例</h3>
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<p class="para">
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<div class="example" id="example-4543">
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<p><strong>Example #1 <span class="function"><strong>pack()</strong></span> 范例</strong></p>
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<div class="example-contents">
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<div class="phpcode"><pre><span style="color: #000000">
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<span style="color: #0000BB"><?php<br />$binarydata </span><span style="color: #007700">= </span><span style="color: #0000BB">pack</span><span style="color: #007700">(</span><span style="color: #DD0000">"nvc*"</span><span style="color: #007700">, </span><span style="color: #0000BB">0x1234</span><span style="color: #007700">, </span><span style="color: #0000BB">0x5678</span><span style="color: #007700">, </span><span style="color: #0000BB">65</span><span style="color: #007700">, </span><span style="color: #0000BB">66</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">?></span>
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</span>
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</pre></div>
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</div>
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<div class="example-contents"><p>
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The resulting binary string will be 6 bytes long and contain
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the byte sequence 0x12, 0x34, 0x78, 0x56, 0x41, 0x42.
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</p></div>
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</div>
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</p>
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</div>
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<div class="refsect1 notes" id="refsect1-function.pack-notes">
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<h3 class="title">注释</h3>
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<div class="caution"><strong class="caution">Caution</strong>
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<p class="para">Note that PHP internally stores <span class="type"><a href="language.types.integer.html" class="type integer">integer</a></span> values as
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signed values of a machine-dependent size (C type <em>long</em>).
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Integer literals and operations that yield numbers outside the bounds of the
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<span class="type"><a href="language.types.integer.html" class="type integer">integer</a></span> type will be stored as <span class="type"><a href="language.types.float.html" class="type float">float</a></span>.
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When packing these floats as integers, they are first cast into the integer
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type. This may or may not result in the desired byte pattern.
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</p>
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<p class="para">The most relevant case is when packing unsigned numbers that would
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be representable with the <span class="type"><a href="language.types.integer.html" class="type integer">integer</a></span> type if it were unsigned.
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In systems where the <span class="type"><a href="language.types.integer.html" class="type integer">integer</a></span> type has a 32-bit size, the cast
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usually results in the same byte pattern as if the <span class="type"><a href="language.types.integer.html" class="type integer">integer</a></span> were
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unsigned (although this relies on implementation-defined unsigned to signed
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conversions, as per the C standard). In systems where the
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<span class="type"><a href="language.types.integer.html" class="type integer">integer</a></span> type has 64_bit size, the <span class="type"><a href="language.types.float.html" class="type float">float</a></span> most
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likely does not have a mantissa large enough to hold the value without
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loss of precision. If those systems also have a native 64-bit C
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<em>int</em> type (most UNIX-like systems don't), the only way to
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use the <em>I</em> pack format in the upper range is to create
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<span class="type"><a href="language.types.integer.html" class="type integer">integer</a></span> negative values with the same byte representation
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as the desired unsigned value.
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</p>
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</div>
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</div>
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<div class="refsect1 seealso" id="refsect1-function.pack-seealso">
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<h3 class="title">参见</h3>
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<p class="para">
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<ul class="simplelist">
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<li class="member"><span class="function"><a href="unpack.html" class="function" rel="rdfs-seeAlso">unpack()</a> - Unpack data from binary string</span></li>
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</ul>
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</p>
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</div>
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</div></div></div></body></html> |