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200 lines
13 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>读取文件（可安全用于二进制文件）</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.fread" class="refentry">
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<div class="refnamediv">
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<h1 class="refname">fread</h1>
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<p class="verinfo">(PHP 4, PHP 5, PHP 7)</p><p class="refpurpose"><span class="refname">fread</span> — <span class="dc-title">读取文件（可安全用于二进制文件）</span></p>
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</div>
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<div class="refsect1 description" id="refsect1-function.fread-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>fread</strong></span>
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( <span class="methodparam"><span class="type">resource</span> <code class="parameter">$handle</code></span>
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, <span class="methodparam"><span class="type">int</span> <code class="parameter">$length</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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<span class="function"><strong>fread()</strong></span> 从文件指针
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<code class="parameter">handle</code> 读取最多
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<code class="parameter">length</code> 个字节。
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该函数在遇上以下几种情况时停止读取文件：
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<ul class="itemizedlist">
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<li class="listitem">
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<span class="simpara">
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读取了 <code class="parameter">length</code> 个字节
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</span>
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</li>
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<li class="listitem">
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<span class="simpara">
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到达了文件末尾（EOF）
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</span>
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</li>
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<li class="listitem">
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<span class="simpara">
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a packet becomes available or the <a href="socket_set_timeout.html" class="link">
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socket timeout</a> occurs (for network streams)
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</span>
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</li>
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<li class="listitem">
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<span class="simpara">
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if the stream is read buffered and it does not represent a plain file, at
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most one read of up to a number of bytes equal to the chunk size (usually
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8192) is made; depending on the previously buffered data, the size of the
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returned data may be larger than the chunk size.
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</span>
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</li>
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</ul>
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</p>
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</div>
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<div class="refsect1 parameters" id="refsect1-function.fread-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">handle</code></dt>
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<dd>
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<p class="para">文件系统指针，是典型地由
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<span class="function"><a href="fopen.html" class="function">fopen()</a></span> 创建的 <span class="type"><a href="language.types.resource.html" class="type resource">resource</a></span>(资源)。</p>
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</dd>
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<dt>
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<code class="parameter">length</code></dt>
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<dd>
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<p class="para">
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最多读取 <code class="parameter">length</code> 个字节。
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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.fread-returnvalues">
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<h3 class="title">返回值</h3>
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<p class="para">
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返回所读取的字符串， 或者在失败时返回 <strong><code>FALSE</code></strong>。
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</p>
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</div>
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<div class="refsect1 examples" id="refsect1-function.fread-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-2801">
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<p><strong>Example #1 一个简单的 <span class="function"><strong>fread()</strong></span> 例子</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 /></span><span style="color: #FF8000">// get contents of a file into a string<br /></span><span style="color: #0000BB">$filename </span><span style="color: #007700">= </span><span style="color: #DD0000">"/usr/local/something.txt"</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">$handle </span><span style="color: #007700">= </span><span style="color: #0000BB">fopen</span><span style="color: #007700">(</span><span style="color: #0000BB">$filename</span><span style="color: #007700">, </span><span style="color: #DD0000">"r"</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">$contents </span><span style="color: #007700">= </span><span style="color: #0000BB">fread</span><span style="color: #007700">(</span><span style="color: #0000BB">$handle</span><span style="color: #007700">, </span><span style="color: #0000BB">filesize</span><span style="color: #007700">(</span><span style="color: #0000BB">$filename</span><span style="color: #007700">));<br /></span><span style="color: #0000BB">fclose</span><span style="color: #007700">(</span><span style="color: #0000BB">$handle</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">?></span>
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</span>
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</pre></div>
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</div>
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</div>
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</p>
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<p class="para">
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<div class="example" id="example-2802">
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<p><strong>Example #2 Binary <span class="function"><strong>fread()</strong></span> example</strong></p>
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<div class="warning"><strong class="warning">Warning</strong>
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<p class="para">
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在区分二进制文件和文本文件的系统上（如
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Windows）打开文件时，<span class="function"><a href="fopen.html" class="function">fopen()</a></span> 函数的 mode 参数要加上 'b'。
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</p>
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</div>
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<div class="example-contents">
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<div class="phpcode"><pre><span style="color: #000000">
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<span style="color: #0000BB"><?php<br />$filename </span><span style="color: #007700">= </span><span style="color: #DD0000">"c:\\files\\somepic.gif"</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">$handle </span><span style="color: #007700">= </span><span style="color: #0000BB">fopen</span><span style="color: #007700">(</span><span style="color: #0000BB">$filename</span><span style="color: #007700">, </span><span style="color: #DD0000">"rb"</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">$contents </span><span style="color: #007700">= </span><span style="color: #0000BB">fread</span><span style="color: #007700">(</span><span style="color: #0000BB">$handle</span><span style="color: #007700">, </span><span style="color: #0000BB">filesize</span><span style="color: #007700">(</span><span style="color: #0000BB">$filename</span><span style="color: #007700">));<br /></span><span style="color: #0000BB">fclose</span><span style="color: #007700">(</span><span style="color: #0000BB">$handle</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>
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</p>
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<p class="para">
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<div class="example" id="example-2803">
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<p><strong>Example #3 Remote <span class="function"><strong>fread()</strong></span> examples</strong></p>
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<div class="warning"><strong class="warning">Warning</strong>
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<p class="para">
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当从任何不是普通本地文件读取时，例如在读取从<a href="features.remote_files.html" class="link">远程文件</a>或
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<span class="function"><a href="popen.html" class="function">popen()</a></span> 以及 <span class="function"><a href="fsockopen.html" class="function">fsockopen()</a></span>
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返回的流时，读取会在一个包可用之后停止。这意味着应该如下例所示将数据收集起来合并成大块。
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</p>
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</div>
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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 /></span><span style="color: #FF8000">// 对 PHP 5 及更高版本<br /></span><span style="color: #0000BB">$handle </span><span style="color: #007700">= </span><span style="color: #0000BB">fopen</span><span style="color: #007700">(</span><span style="color: #DD0000">"http://www.example.com/"</span><span style="color: #007700">, </span><span style="color: #DD0000">"rb"</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">$contents </span><span style="color: #007700">= </span><span style="color: #0000BB">stream_get_contents</span><span style="color: #007700">(</span><span style="color: #0000BB">$handle</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">fclose</span><span style="color: #007700">(</span><span style="color: #0000BB">$handle</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">
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<div class="phpcode"><pre><span style="color: #000000">
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<span style="color: #0000BB"><?php<br />$handle </span><span style="color: #007700">= </span><span style="color: #0000BB">fopen</span><span style="color: #007700">(</span><span style="color: #DD0000">"http://www.example.com/"</span><span style="color: #007700">, </span><span style="color: #DD0000">"rb"</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">$contents </span><span style="color: #007700">= </span><span style="color: #DD0000">''</span><span style="color: #007700">;<br />while (!</span><span style="color: #0000BB">feof</span><span style="color: #007700">(</span><span style="color: #0000BB">$handle</span><span style="color: #007700">)) {<br /> </span><span style="color: #0000BB">$contents </span><span style="color: #007700">.= </span><span style="color: #0000BB">fread</span><span style="color: #007700">(</span><span style="color: #0000BB">$handle</span><span style="color: #007700">, </span><span style="color: #0000BB">8192</span><span style="color: #007700">);<br />}<br /></span><span style="color: #0000BB">fclose</span><span style="color: #007700">(</span><span style="color: #0000BB">$handle</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>
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</p>
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</div>
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<div class="refsect1 notes" id="refsect1-function.fread-notes">
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<h3 class="title">注释</h3>
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<blockquote class="note"><p><strong class="note">Note</strong>:
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<p class="para">
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如果只是想将一个文件的内容读入到一个字符串中，用
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<span class="function"><a href="file_get_contents.html" class="function">file_get_contents()</a></span>，它的性能比上面的代码好得多。
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</p>
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</p></blockquote>
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<blockquote class="note"><p><strong class="note">Note</strong>:
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<p class="para">
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Note that <span class="function"><strong>fread()</strong></span> reads from the current position of
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the file pointer. Use <span class="function"><a href="ftell.html" class="function">ftell()</a></span> to find the current
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position of the pointer and <span class="function"><a href="rewind.html" class="function">rewind()</a></span> to rewind the
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pointer position.
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</p>
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</p></blockquote>
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</div>
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<div class="refsect1 seealso" id="refsect1-function.fread-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="fwrite.html" class="function" rel="rdfs-seeAlso">fwrite()</a> - 写入文件（可安全用于二进制文件）</span></li>
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<li class="member"><span class="function"><a href="fopen.html" class="function" rel="rdfs-seeAlso">fopen()</a> - 打开文件或者 URL</span></li>
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<li class="member"><span class="function"><a href="fsockopen.html" class="function" rel="rdfs-seeAlso">fsockopen()</a> - 打开一个网络连接或者一个Unix套接字连接</span></li>
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<li class="member"><span class="function"><a href="popen.html" class="function" rel="rdfs-seeAlso">popen()</a> - 打开进程文件指针</span></li>
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<li class="member"><span class="function"><a href="fgets.html" class="function" rel="rdfs-seeAlso">fgets()</a> - 从文件指针中读取一行</span></li>
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<li class="member"><span class="function"><a href="fgetss.html" class="function" rel="rdfs-seeAlso">fgetss()</a> - 从文件指针中读取一行并过滤掉 HTML 标记</span></li>
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<li class="member"><span class="function"><a href="fscanf.html" class="function" rel="rdfs-seeAlso">fscanf()</a> - 从文件中格式化输入</span></li>
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<li class="member"><span class="function"><a href="file.html" class="function" rel="rdfs-seeAlso">file()</a> - 把整个文件读入一个数组中</span></li>
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<li class="member"><span class="function"><a href="fpassthru.html" class="function" rel="rdfs-seeAlso">fpassthru()</a> - 输出文件指针处的所有剩余数据</span></li>
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<li class="member"><span class="function"><a href="ftell.html" class="function" rel="rdfs-seeAlso">ftell()</a> - 返回文件指针读/写的位置</span></li>
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<li class="member"><span class="function"><a href="rewind.html" class="function" rel="rdfs-seeAlso">rewind()</a> - 倒回文件指针的位置</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> |