.\" $NetBSD: stddef.3,v 1.8 2011/04/10 10:02:34 jruoho Exp $
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.\" by Jukka Ruohonen.
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.Dd April 10, 2011
.Dt STDDEF 3
.Os
.Sh NAME
.Nm stddef
.Nd standard type definitions
.Sh SYNOPSIS
.In stddef.h
.Sh DESCRIPTION
The
.In stddef.h
header defines the following types and macros:
.Bl -enum -offset 4n
.It
.Vt ptrdiff_t ,
a signed integer type of the result of subtracting two pointers;
.It
.Vt size_t ,
an unsigned integer type of the result of the
.Fn sizeof
operator;
.It
.Vt wchar_t ,
an integer type whose range of values can represent distinct wide-character
codes for all members of the largest character set specified among the
supported locales: the null character has the code value 0 and each member
of the character set has a code value equal to its value when used
as the lone character in an integer character constant;
.It
.Dv NULL ,
which expands to an implementation-defined null pointer constant; and
.It
.Fn offsetof ,
a macro that expands to an integer constant as described in
.Xr offsetof 3 .
.El
.Pp
Some of the described types and macros may appear also in other headers.
.Sh SEE ALSO
.Xr offsetof 3 ,
.Xr stdlib 3 ,
.Xr unistd 3
.Sh STANDARDS
As described here, the
.In stddef.h
header conforms to
.St -isoC-99
and
.St -p1003.1-2001 .
Some of the types and macros conform to earlier standards such as
.St -ansiC .
.Sh HISTORY
In the current form the
.In stddef.h
header was introduced in
.Nx 0.8 ,
the first official release of
.Nx .
Some definitions such as
.Dv NULL
were first introduced already in the
.In nsys/param.h
header of
.At v4 .