linux下判断文件和目录是否存在的方法(总结)
<p><span><strong>1、前言</strong></span></p>
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工作中涉及到文件系统，有时候需要判断文件和目录是否存在。我结合apue第四章文件和目录，总结一下如何正确判断文件和目录是否存在，方便以后查询。</p>
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<span><strong>2、stat系列函数</strong></span></p>
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stat函数用来返回与文件有关的结构信息。stat系列函数有三种情况，分别对应文件名称、文件描述符和符号链接文件。stat结构描述了文件的属性，主要包括文件的类型、文件大小等等。详细stat结构如下所示：</p>
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<code class="xhtml plain">struct stat {</code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">mode_t st_mode; // file type & mode(permissions)</code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">ino_t st_ino; // i-node number(serial number)</code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">dev_t st_dev; // device number(filesystem)</code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">dev_t st_rdev; // device number for specials files</code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">nlink_t st_nlink; // number of links</code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">uid_t st_uid; // user id of owner</code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">gid_t st_gid; // group id of owner</code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">off_t st_size; // size in bytes, for regular files</code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">time_t st_atime; // time of last access</code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">time_t st_mtime; // time of last modification</code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">time_t st_ctime; // time of last file status change</code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">long st_blksize; // best i/o block size</code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">long st_blocks; // number of 512-byte blocks allocated</code>
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<code class="xhtml plain">};</code>
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我们可以通过stat获取文件的类型和文件大小等信息。文件类型有：普通文件、目录文件、块特殊文件、字符特殊文件、fifo、套接字和符号链接。要想通过stat系列函数来判断文件或者目录是否存在，当执行stat函数，如果文件存在时，还需进一步判断该文件是普通文件还是目录文件。</p>
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<span><strong>stat系列函数错误返回-1，错误码存在errno中，errno取值如下：</strong></span></p>
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<code class="xhtml plain">1、enoent 参数file_name 指定的文件不存在</code>
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<code class="xhtml plain">2、enotdir 路径中的目录存在但却非真正的目录</code>
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<code class="xhtml plain">3、eloop 欲打开的文件有过多符号连接问题, 上限为16 符号连接</code>
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<code class="xhtml plain">4、efault 参数buf 为无效指针, 指向无法存在的内存空间</code>
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<code class="xhtml plain">5、eaccess 存取文件时被拒绝</code>
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<code class="xhtml plain">6、enomem 核心内存不足</code>
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<code class="xhtml plain">7、enametoolong 参数file_name 的路径名称太长</code>
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<span><span><strong>3、access函数</strong></span></span></p>
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access函数按照实际用户id和实际组进行访问权限测试。函数原型为：</p>
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<code class="xhtml plain">#include <</code><code class="xhtml keyword">unistd.h</code><code class="xhtml plain">></code>
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<code class="xhtml plain">int access(const char *pathname, int mode);</code>
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<span><strong>mode取值：</strong></span></p>
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f_ok 测试文件是否存在</p>
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r_ok 测试读权限</p>
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w_ok 测试写权限</p>
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x_ok 测试执行权限</p>
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正确判断一个文件是否存在是用access函数，实现如下所示：</p>
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<img title="linux下判断文件和目录是否存在的方法(总结)" alt="linux下判断文件和目录是否存在的方法(总结)" src="https://zhuji.jb51.net/uploads/img/202305/09683a7d15f9f2f9d42e798b4f0ade1e.jpg"></p>
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<span><strong>4、oepndir函数</strong></span></p>
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opendir函数用来打开文件目录，成功返回指针，出错返回null。实现如下：</p>
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<img title="linux下判断文件和目录是否存在的方法(总结)" alt="linux下判断文件和目录是否存在的方法(总结)" src="https://zhuji.jb51.net/uploads/img/202305/367501e67713916615e399d58c116013.jpg"></p>
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以上这篇linux下判断文件和目录是否存在的方法(总结)就是小编分享给大家的全部内容了，希望能给大家一个参考，也希望大家多多支持。</p>
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