.\" Copyright (c) 1991 Regents of the University of California.
.\" All rights reserved.
.\"
.\" %sccs.include.redist.man%
.\"
.\"     @(#)assert.3	6.3 (Berkeley) 04/19/91
.\"
.Dd 
.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 the
.Em stderr
and the function
.Xr _exit 2
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
.Fl NDEBUG
option, see
.Xr cc 1 .
.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\n", \e
		    "expression", __FILE__, __LINE__);
.Ed
.Sh HISTORY
The
.Fn assert
function is
.Ud .