.\" Copyright (c) 1993 by Thomas Koenig (ig25@rz.uni-karlsruhe.de)
.\"
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.\" Modified Sat Jul 24 21:42:42 1993 by Rik Faith <faith@cs.unc.edu>
.\" Modified Tue Oct 22 23:44:11 1996 by Eric S. Raymond <esr@thyrsus.com>
.TH ASSERT 3  2002-08-25 "GNU" "Linux Programmer's Manual"
.SH NAME
assert \- abort the program if assertion is false
.SH SYNOPSIS
.nf
.B #include <assert.h>
.sp
.BI "void assert(scalar " expression );
.fi
.SH DESCRIPTION
If the macro
.B NDEBUG
was defined at the moment
.I <assert.h>
was last included, the macro
.BR assert ()
generates no code, and hence does nothing at all.
Otherwise, the macro
.BR assert ()
prints an error message to standard error and terminates the program
by calling
.BR abort (3)
if
.I expression
is false (i.e., compares equal to zero).
.LP
The purpose of this macro is to help the programmer find bugs in
his program.
The message "assertion failed in file foo.c, function
do_bar(), line 1287" is of no help at all to a user.
.SH RETURN VALUE
No value is returned.
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.TS
allbox;
lb lb lb
l l l.
Interface	Attribute	Value
T{
.BR assert ()
T}	Thread safety	MT-Safe
.TE

.SH CONFORMING TO
POSIX.1-2001, C89, C99.
In C89,
.I expression
is required to be of type
.I int
and undefined behavior results if it is not, but in C99
it may have any scalar type.
.\" See Defect Report 107 for more details.
.SH BUGS
.BR assert ()
is implemented as a macro; if the expression tested has side-effects,
program behavior will be different depending on whether
.B NDEBUG
is defined.
This may create Heisenbugs which go away when debugging
is turned on.
.SH SEE ALSO
.BR abort (3),
.BR assert_perror (3),
.BR exit (3)
.SH COLOPHON
This page is part of release 3.53 of the Linux
.I man-pages
project.
A description of the project,
and information about reporting bugs,
can be found at
\%http://www.kernel.org/doc/man\-pages/.
