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.\" Copyright (c) 1993 by Thomas Koenig (ig25@rz.uni-karlsruhe.de)
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.\"
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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.\" manual page may be incorrect or out-of-date.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.
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.\" Modified Sat Jul 24 21:42:42 1993 by Rik Faith <faith@cs.unc.edu>
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.\" Modified Tue Oct 22 23:44:11 1996 by Eric S. Raymond <esr@thyrsus.com>
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.TH ASSERT 3 2002-08-25 "GNU" "Linux Programmer's Manual"
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.SH NAME
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assert \- abort the program if assertion is false
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.SH SYNOPSIS
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.nf
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.B #include <assert.h>
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.sp
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.BI "void assert(scalar " expression );
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.fi
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.SH DESCRIPTION
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If the macro
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.B NDEBUG
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was defined at the moment
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.I <assert.h>
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was last included, the macro
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.BR assert ()
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generates no code, and hence does nothing at all.
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Otherwise, the macro
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.BR assert ()
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prints an error message to standard error and terminates the program
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by calling
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.BR abort (3)
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if
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.I expression
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is false (i.e., compares equal to zero).
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.LP
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The purpose of this macro is to help the programmer find bugs in
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his program.
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The message "assertion failed in file foo.c, function
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do_bar(), line 1287" is of no help at all to a user.
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.SH "RETURN VALUE"
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No value is returned.
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.SH "CONFORMING TO"
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POSIX.1-2001, C89, C99.
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In C89,
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.I expression
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is required to be of type
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.I int
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and undefined behavior results if it is not, but in C99
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it may have any scalar type.
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.\" See Defect Report 107 for more details.
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.SH BUGS
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.BR assert ()
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is implemented as a macro; if the expression tested has side-effects,
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program behavior will be different depending on whether
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.B NDEBUG
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is defined.
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This may create Heisenbugs which go away when debugging
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is turned on.
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.SH "SEE ALSO"
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.BR abort (3),
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.BR assert_perror (3),
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.BR exit (3)
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