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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>strcmp</title></head><body bgcolor="white"><script type="text/javascript" language="JavaScript" src="../jscript/codes.js"></script><basefont size="3"> <a name="strcmp"></a> <a name="tag_03_722"></a><!-- strcmp --> <!--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_722_01"></a>NAME</h4><blockquote>strcmp - compare two strings</blockquote><h4><a name="tag_03_722_02"></a>SYNOPSIS</h4><blockquote class="synopsis"><p><code><tt>#include <<a href="../basedefs/string.h.html">string.h</a>><br><br> int strcmp(const char *</tt><i>s1</i><tt>, const char *</tt><i>s2</i><tt>);<br></tt></code></p></blockquote><h4><a name="tag_03_722_03"></a>DESCRIPTION</h4><blockquote><div class="box"><sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]"border="0"> The functionality described on this reference page is aligned with the ISO C standard. Any conflict between therequirements described here and the ISO C standard is unintentional. This volume of IEEE Std 1003.1-2001 defers tothe ISO C standard. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></div><p>The <i>strcmp</i>() function shall compare the string pointed to by <i>s1</i> to the string pointed to by <i>s2</i>.</p><p>The sign of a non-zero return value shall be determined by the sign of the difference between the values of the first pair ofbytes (both interpreted as type <b>unsigned char</b>) that differ in the strings being compared.</p></blockquote><h4><a name="tag_03_722_04"></a>RETURN VALUE</h4><blockquote><p>Upon completion, <i>strcmp</i>() shall return an integer greater than, equal to, or less than 0, if the string pointed to by<i>s1</i> is greater than, equal to, or less than the string pointed to by <i>s2</i>, respectively.</p></blockquote><h4><a name="tag_03_722_05"></a>ERRORS</h4><blockquote><p>No errors are defined.</p></blockquote><hr><div class="box"><em>The following sections are informative.</em></div><h4><a name="tag_03_722_06"></a>EXAMPLES</h4><blockquote><h5><a name="tag_03_722_06_01"></a>Checking a Password Entry</h5><p>The following example compares the information read from standard input to the value of the name of the user entry. If the<i>strcmp</i>() function returns 0 (indicating a match), a further check will be made to see if the user entered the proper oldpassword. The <a href="../functions/crypt.html"><i>crypt</i>()</a> function shall encrypt the old password entered by the user,using the value of the encrypted password in the <b>passwd</b> structure as the salt. If this value matches the value of theencrypted <b>passwd</b> in the structure, the entered password <i>oldpasswd</i> is the correct user's password. Finally, theprogram encrypts the new password so that it can store the information in the <b>passwd</b> structure.</p><pre><tt>#include <string.h>#include <unistd.h>#include <stdio.h>...int valid_change;struct passwd *p;char user[100];char oldpasswd[100];char newpasswd[100];char savepasswd[100];...if (strcmp(p->pw_name, user) == 0) { if (strcmp(p->pw_passwd, crypt(oldpasswd, p->pw_passwd)) == 0) { strcpy(savepasswd, crypt(newpasswd, user)); p->pw_passwd = savepasswd; valid_change = 1; } else { fprintf(stderr, "Old password is not valid\n"); }}...</tt></pre></blockquote><h4><a name="tag_03_722_07"></a>APPLICATION USAGE</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_722_08"></a>RATIONALE</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_722_09"></a>FUTURE DIRECTIONS</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_722_10"></a>SEE ALSO</h4><blockquote><p><a href="strncmp.html"><i>strncmp</i>()</a> , the Base Definitions volume of IEEE Std 1003.1-2001, <a href="../basedefs/string.h.html"><i><string.h></i></a></p></blockquote><h4><a name="tag_03_722_11"></a>CHANGE HISTORY</h4><blockquote><p>First released in Issue 1. Derived from Issue 1 of the SVID.</p></blockquote><h4><a name="tag_03_722_12"></a>Issue 6</h4><blockquote><p>Extensions beyond the ISO C standard are marked.</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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