strcmp(3p) — Linux manual page

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

PROLOG

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

NAME

       strcmp — compare two strings

SYNOPSIS

       #include <string.h>

       int strcmp(const char *s1, const char *s2);

DESCRIPTION

       The functionality described on this reference page is aligned
       with the ISO C standard. Any conflict between the requirements
       described here and the ISO C standard is unintentional. This
       volume of POSIX.1‐2017 defers to the ISO C standard.

       The strcmp() function shall compare the string pointed to by s1
       to the string pointed to by s2.

       The sign of a non-zero return value shall be determined by the
       sign of the difference between the values of the first pair of
       bytes (both interpreted as type unsigned char) that differ in the
       strings being compared.

RETURN VALUE

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

ERRORS

       No errors are defined.

       The following sections are informative.

EXAMPLES

   Checking a Password Entry
       The following example compares the information read from standard
       input to the value of the name of the user entry. If the strcmp()
       function returns 0 (indicating a match), a further check will be
       made to see if the user entered the proper old password. The
       crypt() function shall encrypt the old password entered by the
       user, using the value of the encrypted password in the passwd
       structure as the salt. If this value matches the value of the
       encrypted passwd in the structure, the entered password oldpasswd
       is the correct user's password. Finally, the program encrypts the
       new password so that it can store the information in the passwd
       structure.

           #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");
               }
           }
           ...

APPLICATION USAGE

       None.

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

SEE ALSO

       strncmp(3p)

       The Base Definitions volume of POSIX.1‐2017, string.h(0p)

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic
       form from IEEE Std 1003.1-2017, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The
       Open Group Base Specifications Issue 7, 2018 Edition, Copyright
       (C) 2018 by the Institute of Electrical and Electronics
       Engineers, Inc and The Open Group.  In the event of any
       discrepancy between this version and the original IEEE and The
       Open Group Standard, the original IEEE and The Open Group
       Standard is the referee document. The original Standard can be
       obtained online at http://www.opengroup.org/unix/online.html .

       Any typographical or formatting errors that appear in this page
       are most likely to have been introduced during the conversion of
       the source files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group               2017                        STRCMP(3P)

Pages that refer to this page: string.h(0p), hcreate(3p), localeconv(3p), strcoll(3p), strncmp(3p), strxfrm(3p)

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