# strcmp

## 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.
    


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