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.\" $FreeBSD: release/9.1.0/share/man/man9/CTASSERT.9 206622 2010-04-14 19:08:06Z uqs $
.\"
.Dd September 5, 2008
.Dt CTASSERT 9
.Os
.Sh NAME
.Nm CTASSERT
.Nd compile time assertion macro
.Sh SYNOPSIS
.In sys/param.h
.In sys/systm.h
.Fn CTASSERT expression
.Sh DESCRIPTION
The
.Fn CTASSERT
macro evaluates
.Fa expression
at compile time and causes a compiler error if it is false.
.Pp
The
.Fn CTASSERT
macro is useful for asserting the size or alignment of important
data structures and variables during compilation, which would
otherwise cause the code to fail at run time.
.Sh IMPLEMENTATION NOTES
The
.Fn CTASSERT
macro should not be used in a header file.
It is implemented using a dummy typedef, with a name (based on line number)
that may conflict with a
.Fn CTASSERT
in a source file including that header.
.Sh EXAMPLES
Assert that the size of the
.Vt uuid
structure is 16 bytes.
.Pp
.Dl "CTASSERT(sizeof(struct uuid) == 16);"
.Sh SEE ALSO
.Xr KASSERT 9
.Sh AUTHORS
This manual page was written by
.An Hiten M. Pandya
.Aq hmp@FreeBSD.org .