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STRCMP(3P) POSIX Programmer's Manual STRCMP(3P)
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.
strcmp — compare two strings
#include <string.h>
int strcmp(const char *s1, const char *s2);
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.
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.
No errors are defined.
The following sections are informative.
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");
}
}
...
None.
None.
None.
strncmp(3p)
The Base Definitions volume of POSIX.1‐2008, string.h(0p)
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)