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.\" manual page may be incorrect or out-of-date.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