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.\"     @(#)assert.3	8.1 (Berkeley) 6/9/93
.\" $FreeBSD: head/share/man/man3/assert.3 263142 2014-03-14 03:07:51Z eadler $
.\"
.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
.Dv 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 EXAMPLES
The assertion:
.Pp
.Dl "assert(1 == 0);"
.Pp
generates a diagnostic message similar to the following:
.Pp
.Dl "Assertion failed: (1 == 0), function main, file assertion.c, line 100."
.Sh SEE ALSO
.Xr abort 3
.Sh STANDARDS
The
.Fn assert
macro conforms to
.St -isoC-99 .
.Sh HISTORY
An
.Nm
macro appeared in
.At v6 .