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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN"><html><head><!-- Copyright 1997 The Open Group, All Rights Reserved --><title>rand</title></head><body bgcolor=white><center><font size=2>The Single UNIX ® Specification, Version 2<br>Copyright © 1997 The Open Group</font></center><hr size=2 noshade><h4><a name = "tag_000_007_1861"> </a>NAME</h4><blockquote>rand, rand_r - pseudo-random number generator</blockquote><h4><a name = "tag_000_007_1862"> </a>SYNOPSIS</h4><blockquote><pre><code>#include <<a href="stdlib.h.html">stdlib.h</a>>int rand (void);void srand(unsigned int <i>seed</i>);int rand_r(unsigned int *<i>seed</i>);</code></pre></blockquote><h4><a name = "tag_000_007_1863"> </a>DESCRIPTION</h4><blockquote>The<i>rand()</i>function computes a sequence of pseudo-random integers in the range 0 to{RAND_MAX} with a period of at least 2<sup><small>32</small></sup>.<p>The<i><a href="srand.html">srand()</a></i>function uses the argument as a seed for a new sequence ofpseudo-random numbers to be returned by subsequent calls to<i>rand()</i>.If<i><a href="srand.html">srand()</a></i>is then called with the same seed value, the sequence of pseudo-random numberswill be repeated. If<i>rand()</i>is called before any calls to<i><a href="srand.html">srand()</a></i>are made, the same sequence will be generated as when<i><a href="srand.html">srand()</a></i>is first called with a seed value of 1.<p>The implementation will behave as if no function defined in this document calls<i>rand()</i>or<i>srand</i>.<p>The<i>rand()</i>interface need not be reentrant.<p>The<i>rand_r()</i>function computes a sequence of pseudo-random integersin the range 0 to {RAND_MAX}.(The value of the {RAND_MAX}macro will be at least 32767.)<p>If<i>rand_r()</i>is called with the same initial value for the object pointed to by<i>seed</i>and that object is not modified between successive returns and calls to<i>rand_r()</i>,the same sequence shall be generated.</blockquote><h4><a name = "tag_000_007_1864"> </a>RETURN VALUE</h4><blockquote>The<i>rand()</i>function returns the next pseudo-random number in the sequence. The<i><a href="srand.html">srand()</a></i>function returns no value.<p>The<i>rand_r()</i>function returns a pseudo-random integer.</blockquote><h4><a name = "tag_000_007_1865"> </a>ERRORS</h4><blockquote>No errors are defined.</blockquote><h4><a name = "tag_000_007_1866"> </a>EXAMPLES</h4><blockquote>None.</blockquote><h4><a name = "tag_000_007_1867"> </a>APPLICATION USAGE</h4><blockquote>The<i><a href="drand48.html">drand48()</a></i>function provides a much more elaborate random number generator.<p>The following code defines a pair of functions which couldbe incorporated into applications wishing to ensure that thesame sequence of numbers is generated across different machines:<pre><code>static unsigned long int next = 1;int myrand(void) /* RAND_MAX assumed to be 32767 */{ next = next * 1103515245 + 12345; return((unsigned int)(next/65536) % 32768);}void mysrand(unsigned int seed){ next = seed;}</code></pre></blockquote><h4><a name = "tag_000_007_1868"> </a>FUTURE DIRECTIONS</h4><blockquote>None.</blockquote><h4><a name = "tag_000_007_1869"> </a>SEE ALSO</h4><blockquote><i><a href="drand48.html">drand48()</a></i>,<i><a href="srand.html">srand()</a></i>,<i><a href="stdlib.h.html"><stdlib.h></a></i>.</blockquote><h4>DERIVATION</h4><blockquote><i>rand()</i> derived from Issue 1 of the SVID.<P><i>rand_r()</i> derived from the POSIX Threads Extension (1003.1c-1995).</blockquote><hr size=2 noshade><center><font size=2>UNIX ® is a registered Trademark of The Open Group.<br>Copyright © 1997 The Open Group<br> [ <a href="../index.html">Main Index</a> | <a href="../xshix.html">XSH</a> | <a href="../xcuix.html">XCU</a> | <a href="../xbdix.html">XBD</a> | <a href="../cursesix.html">XCURSES</a> | <a href="../xnsix.html">XNS</a> ]</font></center><hr size=2 noshade></body></html>⌨️ 快捷键说明
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