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PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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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.1‐2017 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.
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.1‐2017, string.h(0p)
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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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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