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PROLOG |NAME |SYNOPSIS |DESCRIPTION |RETURN VALUE |ERRORS |EXAMPLES |APPLICATION USAGE |RATIONALE |FUTURE DIRECTIONS |SEE ALSO |COPYRIGHT | |
STRCMP(3P) POSIX Programmer's ManualSTRCMP(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. Thestrcmp() function shall compare the string pointed to bys1 to the string pointed to bys2. 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 typeunsigned 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 bys1 is greater than, equal to, or less than the string pointed to bys2, 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 thestrcmp() function returns 0 (indicating a match), a further check will be made to see if the user entered the proper old password. Thecrypt() function shall encrypt the old password entered by the user, using the value of the encrypted password in thepasswd structure as the salt. If this value matches the value of the encryptedpasswdin the structure, the entered passwordoldpasswd is the correct user's password. Finally, the program encrypts the new password so that it can store the information in thepasswd 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.
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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 athttp://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, seehttps://www.kernel.org/doc/man-pages/reporting_bugs.html .IEEE/The Open Group 2017STRCMP(3P)Pages that refer to this page:string.h(0p), hcreate(3p), localeconv(3p), strcoll(3p), strncmp(3p), strxfrm(3p)
HTML rendering created 2025-09-06 byMichael Kerrisk, author ofThe Linux Programming Interface. For details of in-depthLinux/UNIX system programming training courses that I teach, lookhere. Hosting byjambit GmbH. | |