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when to use assert, as well as providing a bad example of using assert. While not strictly necessary, experience has shown issues with poor assert choice happen often enough that this departure seems warranted. Also, tighten up the previous example (there's no need to have extra paragraphs or gratuitously long lines). Reviewed by: emaste@ (earlier version)
111 lines
3.3 KiB
Groff
111 lines
3.3 KiB
Groff
.\" Copyright (c) 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)assert.3 8.1 (Berkeley) 6/9/93
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.\" $FreeBSD$
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.\"
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.Dd May 31, 2018
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.Dt ASSERT 3
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.Os
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.Sh NAME
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.Nm assert
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.Nd expression verification macro
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.Sh SYNOPSIS
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.In assert.h
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.Fn assert expression
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.Sh DESCRIPTION
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The
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.Fn assert
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macro tests the given
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.Ar expression
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and if it is false,
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the calling process is terminated.
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A diagnostic message is written to
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.Dv stderr
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and the function
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.Xr abort 3
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is called, effectively terminating the program.
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.Pp
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If
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.Ar expression
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is true,
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the
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.Fn assert
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macro does nothing.
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.Pp
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The
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.Fn assert
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macro
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may be removed at compile time by defining
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.Dv NDEBUG
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as a macro
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(e.g., by using the
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.Xr cc 1
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option
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.Fl D Ns Dv NDEBUG ) .
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Unlike most other include files,
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.In assert.h
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may be included multiple times.
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Each time whether or not
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.Dv NDEBUG
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is defined determines the behavior of assert from that point forward
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until the end of the unit or another include of
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.In assert.h .
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.Pp
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The
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.Fn assert
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macro should only be used for ensuring the developer's expectations
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hold true.
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It is not appropriate for regular run-time error detection.
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.Sh EXAMPLES
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The assertion:
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.Dl "assert(1 == 0);"
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generates a diagnostic message similar to the following:
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.Dl "Assertion failed: (1 == 0), function main, file main.c, line 100."
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.Pp
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The following assert tries to assert there was no partial read:
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.Dl "assert(read(fd, buf, nbytes) == nbytes);"
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However, there are two problems.
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First, it checks for normal conditions, rather than conditions that
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indicate a bug.
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Second, the code will disappear if
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.Dv NDEBUG
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is defined, changing the semantics of the program.
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.Sh SEE ALSO
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.Xr abort2 2 ,
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.Xr abort 3
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.Sh STANDARDS
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The
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.Fn assert
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macro conforms to
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.St -isoC-99 .
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.Sh HISTORY
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An
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.Nm
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macro appeared in
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.At v7 .
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