1STRCMP(3P)                 POSIX Programmer's Manual                STRCMP(3P)
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PROLOG

6       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
7       implementation of this interface may differ (consult the  corresponding
8       Linux  manual page for details of Linux behavior), or the interface may
9       not be implemented on Linux.
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NAME

12       strcmp — compare two strings
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SYNOPSIS

15       #include <string.h>
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17       int strcmp(const char *s1, const char *s2);
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DESCRIPTION

20       The functionality described on this reference page is aligned with  the
21       ISO C  standard.  Any  conflict between the requirements described here
22       and the ISO C standard is unintentional. This  volume  of  POSIX.1‐2017
23       defers to the ISO C standard.
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25       The  strcmp() function shall compare the string pointed to by s1 to the
26       string pointed to by s2.
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28       The sign of a non-zero return value shall be determined by the sign  of
29       the  difference  between  the  values  of the first pair of bytes (both
30       interpreted as type unsigned char) that differ  in  the  strings  being
31       compared.
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RETURN VALUE

34       Upon  completion,  strcmp() shall return an integer greater than, equal
35       to, or less than 0, if the string pointed to by  s1  is  greater  than,
36       equal to, or less than the string pointed to by s2, respectively.
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ERRORS

39       No errors are defined.
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41       The following sections are informative.
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EXAMPLES

44   Checking a Password Entry
45       The following example compares the information read from standard input
46       to the value of the name of the user entry. If  the  strcmp()  function
47       returns  0 (indicating a match), a further check will be made to see if
48       the user entered the proper old password. The  crypt()  function  shall
49       encrypt  the  old  password entered by the user, using the value of the
50       encrypted password in the passwd structure as the salt. If  this  value
51       matches the value of the encrypted passwd in the structure, the entered
52       password oldpasswd is the correct user's password. Finally, the program
53       encrypts  the  new password so that it can store the information in the
54       passwd structure.
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56
57           #include <string.h>
58           #include <unistd.h>
59           #include <stdio.h>
60           ...
61           int valid_change;
62           struct passwd *p;
63           char user[100];
64           char oldpasswd[100];
65           char newpasswd[100];
66           char savepasswd[100];
67           ...
68           if (strcmp(p->pw_name, user) == 0) {
69               if (strcmp(p->pw_passwd, crypt(oldpasswd, p->pw_passwd)) == 0) {
70                   strcpy(savepasswd, crypt(newpasswd, user));
71                   p->pw_passwd = savepasswd;
72                   valid_change = 1;
73               }
74               else {
75                   fprintf(stderr, "Old password is not valid\n");
76               }
77           }
78           ...
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APPLICATION USAGE

81       None.
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RATIONALE

84       None.
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FUTURE DIRECTIONS

87       None.
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SEE ALSO

90       strncmp()
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92       The Base Definitions volume of POSIX.1‐2017, <string.h>
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95       Portions of this text are reprinted and reproduced in  electronic  form
96       from  IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
97       table Operating System Interface (POSIX), The Open Group Base  Specifi‐
98       cations  Issue  7, 2018 Edition, Copyright (C) 2018 by the Institute of
99       Electrical and Electronics Engineers, Inc and The Open Group.   In  the
100       event of any discrepancy between this version and the original IEEE and
101       The Open Group Standard, the original IEEE and The Open Group  Standard
102       is  the  referee document. The original Standard can be obtained online
103       at http://www.opengroup.org/unix/online.html .
104
105       Any typographical or formatting errors that appear  in  this  page  are
106       most likely to have been introduced during the conversion of the source
107       files to man page format. To report such errors,  see  https://www.ker
108       nel.org/doc/man-pages/reporting_bugs.html .
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112IEEE/The Open Group                  2017                           STRCMP(3P)
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