strcmp(3p) [suse man 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 correspond- ing 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 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() func- tion 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 "); } } ... APPLICATION USAGE
None. RATIONALE
None. FUTURE DIRECTIONS
None. SEE ALSO
strncmp(), the Base Definitions volume of IEEE Std 1003.1-2001, <string.h> COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technol- ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 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 . IEEE
/The Open Group 2003 STRCMP(3P)
Check Out this Related Man Page
CRYPT(3P) POSIX Programmer's Manual CRYPT(3P) PROLOG
This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the correspond- ing Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux. NAME
crypt - string encoding function (CRYPT) SYNOPSIS
#include <unistd.h> char *crypt(const char *key, const char *salt); DESCRIPTION
The crypt() function is a string encoding function. The algorithm is implementation-defined. The key argument points to a string to be encoded. The salt argument is a string chosen from the set: a b c d e f g h i j k l m n o p q r s t u v w x y z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z 0 1 2 3 4 5 6 7 8 9 . / The first two characters of this string may be used to perturb the encoding algorithm. The return value of crypt() points to static data that is overwritten by each call. The crypt() function need not be reentrant. A function that is not required to be reentrant is not required to be thread-safe. RETURN VALUE
Upon successful completion, crypt() shall return a pointer to the encoded string. The first two characters of the returned value shall be those of the salt argument. Otherwise, it shall return a null pointer and set errno to indicate the error. ERRORS
The crypt() function shall fail if: ENOSYS The functionality is not supported on this implementation. The following sections are informative. EXAMPLES
Encoding Passwords The following example finds a user database entry matching a particular user name and changes the current password to a new password. The crypt() function generates an encoded version of each password. The first call to crypt() produces an encoded version of the old password; that encoded password is then compared to the password stored in the user database. The second call to crypt() encodes the new password before it is stored. The putpwent() function, used in the following example, is not part of IEEE Std 1003.1-2001. #include <unistd.h> #include <pwd.h> #include <string.h> #include <stdio.h> ... int valid_change; int pfd; /* Integer for file descriptor returned by open(). */ FILE *fpfd; /* File pointer for use in putpwent(). */ struct passwd *p; char user[100]; char oldpasswd[100]; char newpasswd[100]; char savepasswd[100]; ... valid_change = 0; while ((p = getpwent()) != NULL) { /* Change entry if found. */ 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 "); } } /* Put passwd entry into ptmp. */ putpwent(p, fpfd); } APPLICATION USAGE
The values returned by this function need not be portable among XSI-conformant systems. RATIONALE
None. FUTURE DIRECTIONS
None. SEE ALSO
encrypt(), setkey(), the Base Definitions volume of IEEE Std 1003.1-2001, <unistd.h> COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technol- ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 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 . IEEE
/The Open Group 2003 CRYPT(3P)