📄 unsetenv.html
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html><head><meta name="generator" content="HTML Tidy, see www.w3.org"><meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"><link type="text/css" rel="stylesheet" href="style.css"><!-- Generated by The Open Group's rhtm tool v1.2.1 --><!-- Copyright (c) 2001-2003 The Open Group, All Rights Reserved --><title>unsetenv</title></head><body bgcolor="white"><script type="text/javascript" language="JavaScript" src="../jscript/codes.js"></script><basefont size="3"> <a name="unsetenv"></a> <a name="tag_03_804"></a><!-- unsetenv --> <!--header start--><center><font size="2">The Open Group Base Specifications Issue 6<br>IEEE Std 1003.1, 2003 Edition<br>Copyright © 2001-2003 The IEEE and The Open Group, All Rights reserved.</font></center><!--header end--><hr size="2" noshade><h4><a name="tag_03_804_01"></a>NAME</h4><blockquote>unsetenv - remove an environment variable</blockquote><h4><a name="tag_03_804_02"></a>SYNOPSIS</h4><blockquote class="synopsis"><div class="box"><code><tt><sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> #include <<a href="../basedefs/stdlib.h.html">stdlib.h</a>><br><br> int unsetenv(const char *</tt><i>name</i><tt>); <img src="../images/opt-end.gif" alt="[Option End]" border="0"></tt></code></div><tt><br></tt></blockquote><h4><a name="tag_03_804_03"></a>DESCRIPTION</h4><blockquote><p>The <i>unsetenv</i>() function shall remove an environment variable from the environment of the calling process. The <i>name</i>argument points to a string, which is the name of the variable to be removed. The named argument shall not contain an <tt>'='</tt>character. If the named variable does not exist in the current environment, the environment shall be unchanged and the function isconsidered to have completed successfully.</p><p>If the application modifies <i>environ</i> or the pointers to which it points, the behavior of <i>unsetenv</i>() is undefined.The <i>unsetenv</i>() function shall update the list of pointers to which <i>environ</i> points.</p><p>The <i>unsetenv</i>() function need not be reentrant. A function that is not required to be reentrant is not required to bethread-safe.</p></blockquote><h4><a name="tag_03_804_04"></a>RETURN VALUE</h4><blockquote><p>Upon successful completion, zero shall be returned. Otherwise, -1 shall be returned, <i>errno</i> set to indicate the error, andthe environment shall be unchanged.</p></blockquote><h4><a name="tag_03_804_05"></a>ERRORS</h4><blockquote><p>The <i>unsetenv</i>() function shall fail if:</p><dl compact><dt>[EINVAL]</dt><dd>The <i>name</i> argument is a null pointer, points to an empty string, or points to a string containing an <tt>'='</tt>character.</dd></dl></blockquote><hr><div class="box"><em>The following sections are informative.</em></div><h4><a name="tag_03_804_06"></a>EXAMPLES</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_804_07"></a>APPLICATION USAGE</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_804_08"></a>RATIONALE</h4><blockquote><p>Refer to the RATIONALE section in <a href="setenv.html"><i>setenv</i>()</a> .</p></blockquote><h4><a name="tag_03_804_09"></a>FUTURE DIRECTIONS</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_804_10"></a>SEE ALSO</h4><blockquote><p><a href="getenv.html"><i>getenv</i>()</a> , <a href="setenv.html"><i>setenv</i>()</a> , the Base Definitions volume ofIEEE Std 1003.1-2001, <a href="../basedefs/stdlib.h.html"><i><stdlib.h></i></a>, <a href="../basedefs/sys/types.h.html"><i><sys/types.h></i></a>, <a href="../basedefs/unistd.h.html"><i><unistd.h></i></a></p></blockquote><h4><a name="tag_03_804_11"></a>CHANGE HISTORY</h4><blockquote><p>First released in Issue 6. Derived from the IEEE P1003.1a draft standard.</p></blockquote><div class="box"><em>End of informative text.</em></div><hr><hr size="2" noshade><center><font size="2"><!--footer start-->UNIX ® is a registered Trademark of The Open Group.<br>POSIX ® is a registered Trademark of The IEEE.<br>[ <a href="../mindex.html">Main Index</a> | <a href="../basedefs/contents.html">XBD</a> | <a href="../utilities/contents.html">XCU</a> | <a href="../functions/contents.html">XSH</a> | <a href="../xrat/contents.html">XRAT</a>]</font></center><!--footer end--><hr size="2" noshade></body></html>⌨️ 快捷键说明
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