.\"	$OpenBSD: assert.3,v 1.6 2003/06/02 23:30:12 millert Exp $
.\"	$NetBSD: assert.3,v 1.5 1994/11/30 15:24:30 jtc Exp $
.\"
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.\"     @(#)assert.3	8.1 (Berkeley) 6/9/93
.\"
.Dd June 9, 1993
.Dt ASSERT 3
.Os
.Sh NAME
.Nm assert
.Nd expression verification macro
.Sh SYNOPSIS
.Fd #include <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
.Xr abort 3
function 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 with the
.Xr cc 1
option
.Fl DNDEBUG .
.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 cc 1 ,
.Xr abort 3
.Sh STANDARDS
The
.Fn assert
macro conforms to
.St -ansiC .
.Sh HISTORY
An
.Fn assert
macro appeared in
.At v6 .