PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT

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

PROLOG         top

       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         top

       strcmp — compare two strings

SYNOPSIS         top

       #include <string.h>

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

DESCRIPTION         top

       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.1‐2008 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         top

       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         top

       No errors are defined.

       The following sections are informative.

EXAMPLES         top

   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         top

       None.

RATIONALE         top

       None.

FUTURE DIRECTIONS         top

       None.

SEE ALSO         top

       strncmp(3p)

       The Base Definitions volume of POSIX.1‐2008, string.h(0p)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The Open
       Group Base Specifications Issue 7, Copyright (C) 2013 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
       applied.) 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.unix.org/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                 2013                          STRCMP(3P)

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