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.\"     @(#)assert.3	8.1 (Berkeley) 6/9/93
.\" $FreeBSD: src/share/man/man3/assert.3,v 1.7.2.3 2001/12/17 11:30:11 ru Exp $
.\" $DragonFly: src/share/man/man3/assert.3,v 1.2 2003/06/17 04:36:58 dillon Exp $
.\"
.Dd January 26, 1999
.Dt ASSERT 3
.Os
.Sh NAME
.Nm assert
.Nd expression verification macro
.Sh SYNOPSIS
.In assert.h
.Fn assert expression
.Sh DESCRIPTION
The
.Fn assert
macro tests the given
.Ar expression
and if it is false,
the calling process is terminated.
A
diagnostic message is written to
.Em stderr
and the function
.Xr abort 3
is called, effectively terminating the program.
.Pp
If
.Ar expression
is true,
the
.Fn assert
macro does nothing.
.Pp
The
.Fn assert
macro
may be removed at compile time by defining
.Dv NDEBUG
as a macro
(e.g., by using the
.Xr cc 1
option
.Fl D Ns Dv NDEBUG ) .
.Sh DIAGNOSTICS
The following diagnostic message is written to
.Em stderr
if
.Ar expression
is false:
.Bd -literal -offset indent
"assertion \e"%s\e" failed: file \e"%s\e", line %d\en", \e
		    "expression", __FILE__, __LINE__);
.Ed
.Sh SEE ALSO
.Xr abort 3
.Sh HISTORY
An
.Nm
macro appeared in
.At v6 .