156 lines
5.5 KiB
HTML
156 lines
5.5 KiB
HTML
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<!-- Copyright (c) 2001 The Open Group, All Rights Reserved -->
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<title>putenv</title>
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<body bgcolor="white">
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<script type="text/javascript" language="JavaScript" src="../jscript/codes.js">
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<basefont size="3"> <a name="putenv"></a> <a name="tag_03_583"></a><!-- putenv -->
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<!--header start-->
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<center><font size="2">The Open Group Base Specifications Issue 6<br>
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IEEE Std 1003.1-2001<br>
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Copyright © 2001 The IEEE and The Open Group, All Rights reserved.</font></center>
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<!--header end-->
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<hr size="2" noshade>
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<h4><a name="tag_03_583_01"></a>NAME</h4>
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<blockquote>putenv - change or add a value to an environment</blockquote>
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<h4><a name="tag_03_583_02"></a>SYNOPSIS</h4>
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<blockquote class="synopsis">
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<div class="box"><code><tt><sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt=
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"[Option Start]" border="0"> #include <<a href="../basedefs/stdlib.h.html">stdlib.h</a>><br>
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<br>
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int putenv(char *</tt><i>string</i><tt>); <img src="../images/opt-end.gif" alt="[Option End]" border="0"></tt></code></div>
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<tt><br>
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</tt></blockquote>
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<h4><a name="tag_03_583_03"></a>DESCRIPTION</h4>
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<blockquote>
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<p>The <i>putenv</i>() function shall use the <i>string</i> argument to set environment variable values. The <i>string</i> argument
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should point to a string of the form " <i>name</i>= <i>value</i>. The <i>putenv</i>() function shall make the value of the
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environment variable <i>name</i> equal to <i>value</i> by altering an existing variable or creating a new one. In either case, the
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string pointed to by <i>string</i> shall become part of the environment, so altering the string shall change the environment. The
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space used by <i>string</i> is no longer used once a new string-defining <i>name</i> is passed to <i>putenv</i>().</p>
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<p>The <i>putenv</i>() function need not be reentrant. A function that is not required to be reentrant is not required to be
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thread-safe.</p>
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</blockquote>
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<h4><a name="tag_03_583_04"></a>RETURN VALUE</h4>
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<blockquote>
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<p>Upon successful completion, <i>putenv</i>() shall return 0; otherwise, it shall return a non-zero value and set <i>errno</i> to
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indicate the error.</p>
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</blockquote>
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<h4><a name="tag_03_583_05"></a>ERRORS</h4>
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<blockquote>
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<p>The <i>putenv</i>() function may fail if:</p>
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<dl compact>
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<dt>[ENOMEM]</dt>
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<dd>Insufficient memory was available.</dd>
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</dl>
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</blockquote>
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<hr>
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<div class="box"><em>The following sections are informative.</em></div>
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<h4><a name="tag_03_583_06"></a>EXAMPLES</h4>
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<blockquote>
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<h5><a name="tag_03_583_06_01"></a>Changing the Value of an Environment Variable</h5>
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<p>The following example changes the value of the <i>HOME</i> environment variable to the value <b>/usr/home</b>.</p>
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<pre>
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<tt>#include <stdlib.h>
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...
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static char *var = "HOME=/usr/home";
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int ret;
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<br>
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ret = putenv(var);
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</tt>
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</pre>
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</blockquote>
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<h4><a name="tag_03_583_07"></a>APPLICATION USAGE</h4>
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<blockquote>
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<p>The <i>putenv</i>() function manipulates the environment pointed to by <i>environ</i>, and can be used in conjunction with <a
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href="../functions/getenv.html"><i>getenv</i>()</a>.</p>
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<p>This routine may use <a href="../functions/malloc.html"><i>malloc</i>()</a> to enlarge the environment.</p>
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<p>A potential error is to call <i>putenv</i>() with an automatic variable as the argument, then return from the calling function
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while <i>string</i> is still part of the environment.</p>
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<p>The <a href="../functions/setenv.html"><i>setenv</i>()</a> function is preferred over this function.</p>
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</blockquote>
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<h4><a name="tag_03_583_08"></a>RATIONALE</h4>
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<blockquote>
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<p>The standard developers noted that <i>putenv</i>() is the only function available to add to the environment without permitting
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memory leaks.</p>
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</blockquote>
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<h4><a name="tag_03_583_09"></a>FUTURE DIRECTIONS</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_583_10"></a>SEE ALSO</h4>
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<blockquote>
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<p><a href="exec.html"><i><a href="../functions/exec.html">exec</a></i>()</a> , <a href="getenv.html"><i>getenv</i>()</a> , <a
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href="malloc.html"><i>malloc</i>()</a> , <a href="setenv.html"><i>setenv</i>()</a> , the Base Definitions volume of
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IEEE Std 1003.1-2001, <a href="../basedefs/stdlib.h.html"><i><stdlib.h></i></a></p>
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</blockquote>
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<h4><a name="tag_03_583_11"></a>CHANGE HISTORY</h4>
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<blockquote>
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<p>First released in Issue 1. Derived from Issue 1 of the SVID.</p>
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</blockquote>
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<h4><a name="tag_03_583_12"></a>Issue 5</h4>
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<blockquote>
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<p>The type of the argument to this function is changed from <b>const char *</b> to <b>char *</b>. This was indicated as a FUTURE
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DIRECTION in previous issues.</p>
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<p>A note indicating that this function need not be reentrant is added to the DESCRIPTION.</p>
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</blockquote>
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<div class="box"><em>End of informative text.</em></div>
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