| .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk) |
| .\" and Copyright 2020 Michael Kerrisk <mtk.manpages@gmail.com> |
| .\" |
| .\" %%%LICENSE_START(VERBATIM) |
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| .\" preserved on all copies. |
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| .\" Permission is granted to copy and distribute modified versions of this |
| .\" manual under the conditions for verbatim copying, provided that the |
| .\" entire resulting derived work is distributed under the terms of a |
| .\" permission notice identical to this one. |
| .\" |
| .\" Since the Linux kernel and libraries are constantly changing, this |
| .\" manual page may be incorrect or out-of-date. The author(s) assume no |
| .\" responsibility for errors or omissions, or for damages resulting from |
| .\" the use of the information contained herein. The author(s) may not |
| .\" have taken the same level of care in the production of this manual, |
| .\" which is licensed free of charge, as they might when working |
| .\" professionally. |
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| .\" Formatted or processed versions of this manual, if unaccompanied by |
| .\" the source, must acknowledge the copyright and authors of this work. |
| .\" %%%LICENSE_END |
| .\" |
| .\" References consulted: |
| .\" Linux libc source code |
| .\" Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991) |
| .\" 386BSD man pages |
| .\" Modified Sat Jul 24 18:08:52 1993 by Rik Faith (faith@cs.unc.edu) |
| .\" Modified 2001-08-31, aeb |
| .\" |
| .TH STRCMP 3 2021-03-22 "" "Linux Programmer's Manual" |
| .SH NAME |
| strcmp, strncmp \- compare two strings |
| .SH SYNOPSIS |
| .nf |
| .B #include <string.h> |
| .PP |
| .BI "int strcmp(const char *" s1 ", const char *" s2 ); |
| .BI "int strncmp(const char *" s1 ", const char *" s2 ", size_t " n ); |
| .fi |
| .SH DESCRIPTION |
| The |
| .BR strcmp () |
| function compares the two strings |
| .I s1 |
| and |
| .IR s2 . |
| The locale is not taken into account (for a locale-aware comparison, see |
| .BR strcoll (3)). |
| The comparison is done using unsigned characters. |
| .PP |
| .BR strcmp () |
| returns an integer indicating the result of the comparison, as follows: |
| .IP \(bu 2 |
| 0, if the |
| .I s1 |
| and |
| .I s2 |
| are equal; |
| .IP \(bu |
| a negative value if |
| .I s1 |
| is less than |
| .IR s2 ; |
| .IP \(bu |
| a positive value if |
| .I s1 |
| is greater than |
| .IR s2 . |
| .PP |
| The |
| .BR strncmp () |
| function is similar, except it compares |
| only the first (at most) |
| .IR n |
| bytes of |
| .I s1 |
| and |
| .IR s2 . |
| .SH RETURN VALUE |
| The |
| .BR strcmp () |
| and |
| .BR strncmp () |
| functions return an integer |
| less than, equal to, or greater than zero if |
| .I s1 |
| (or the first |
| .I n |
| bytes thereof) is found, respectively, to be less than, to |
| match, or be greater than |
| .IR s2 . |
| .SH ATTRIBUTES |
| For an explanation of the terms used in this section, see |
| .BR attributes (7). |
| .ad l |
| .nh |
| .TS |
| allbox; |
| lbx lb lb |
| l l l. |
| Interface Attribute Value |
| T{ |
| .BR strcmp (), |
| .BR strncmp () |
| T} Thread safety MT-Safe |
| .TE |
| .hy |
| .ad |
| .sp 1 |
| .SH CONFORMING TO |
| POSIX.1-2001, POSIX.1-2008, C89, C99, SVr4, 4.3BSD. |
| .SH NOTES |
| POSIX.1 specifies only that: |
| .RS |
| .PP |
| The sign of a nonzero return value shall be determined by the sign |
| of the difference between the values of the first pair of bytes |
| (both interpreted as type |
| .IR "unsigned char" ) |
| that differ in the strings being compared. |
| .RE |
| .PP |
| In glibc, as in most other implementations, |
| the return value is the arithmetic result of subtracting |
| the last compared byte in |
| .I s2 |
| from the last compared byte in |
| .IR s1 . |
| (If the two characters are equal, this difference is 0.) |
| .SH EXAMPLES |
| The program below can be used to demonstrate the operation of |
| .BR strcmp () |
| (when given two arguments) and |
| .BR strncmp () |
| (when given three arguments). |
| First, some examples using |
| .BR strcmp (): |
| .PP |
| .in +4n |
| .EX |
| $ \fB./string_comp ABC ABC\fP |
| <str1> and <str2> are equal |
| $ \fB./string_comp ABC AB\fP # \(aqC\(aq is ASCII 67; \(aqC\(aq \- \(aq\0\(aq = 67 |
| <str1> is greater than <str2> (67) |
| $ \fB./string_comp ABA ABZ\fP # \(aqA\(aq is ASCII 65; \(aqZ\(aq is ASCII 90 |
| <str1> is less than <str2> (\-25) |
| $ \fB./string_comp ABJ ABC\fP |
| <str1> is greater than <str2> (7) |
| $ .\fB/string_comp $\(aq\e201\(aq A\fP # 0201 \- 0101 = 0100 (or 64 decimal) |
| <str1> is greater than <str2> (64) |
| .EE |
| .in |
| .PP |
| The last example uses |
| .BR bash (1)-specific |
| syntax to produce a string containing an 8-bit ASCII code; |
| the result demonstrates that the string comparison uses unsigned |
| characters. |
| .PP |
| And then some examples using |
| .BR strncmp (): |
| .PP |
| .in +4n |
| .EX |
| $ \fB./string_comp ABC AB 3\fP |
| <str1> is greater than <str2> (67) |
| $ \fB./string_comp ABC AB 2\fP |
| <str1> and <str2> are equal in the first 2 bytes |
| .EE |
| .in |
| .SS Program source |
| \& |
| .EX |
| /* string_comp.c |
| |
| Licensed under GNU General Public License v2 or later. |
| */ |
| #include <stdio.h> |
| #include <stdlib.h> |
| #include <string.h> |
| |
| int |
| main(int argc, char *argv[]) |
| { |
| int res; |
| |
| if (argc < 3) { |
| fprintf(stderr, "Usage: %s <str1> <str2> [<len>]\en", argv[0]); |
| exit(EXIT_FAILURE); |
| } |
| |
| if (argc == 3) |
| res = strcmp(argv[1], argv[2]); |
| else |
| res = strncmp(argv[1], argv[2], atoi(argv[3])); |
| |
| if (res == 0) { |
| printf("<str1> and <str2> are equal"); |
| if (argc > 3) |
| printf(" in the first %d bytes\en", atoi(argv[3])); |
| printf("\en"); |
| } else if (res < 0) { |
| printf("<str1> is less than <str2> (%d)\en", res); |
| } else { |
| printf("<str1> is greater than <str2> (%d)\en", res); |
| } |
| |
| exit(EXIT_SUCCESS); |
| } |
| .EE |
| .SH SEE ALSO |
| .BR bcmp (3), |
| .BR memcmp (3), |
| .BR strcasecmp (3), |
| .BR strcoll (3), |
| .BR string (3), |
| .BR strncasecmp (3), |
| .BR strverscmp (3), |
| .BR wcscmp (3), |
| .BR wcsncmp (3), |
| .BR ascii (7) |