The Open Group Base Specifications Issue 6
IEEE Std 1003.1, 2004 Edition
Copyright © 2001-2004 The IEEE and The Open Group, All Rights reserved.

#### NAME

> stddef.h - standard type definitions

#### SYNOPSIS

> `#include <stddef.h>`

#### DESCRIPTION

> [CX] The functionality described on this reference page is aligned with the ISO C standard. Any conflict between the requirements described here and the ISO C standard is unintentional. This volume of IEEE Std 1003.1-2001 defers to the ISO C standard.

> The <stddef.h> header shall define the following macros:

> NULL
>   Null pointer constant.
> offsetof(type, member-designator)
>   Integer constant expression of type size_t, the value of which is the offset in bytes to the structure member (member-designator), from the beginning of its structure (type).

> The <stddef.h> header shall define the following types:

> ptrdiff_t
>   Signed integer type of the result of subtracting two pointers.
> wchar_t
>   Integer type whose range of values can represent distinct wide-character codes for all members of the largest character set specified among the locales supported by the compilation environment: the null character has the code value 0 and each member of the portable character set has a code value equal to its value when used as the lone character in an integer character constant.
> size_t
>   Unsigned integer type of the result of the sizeof operator.

> The implementation shall support one or more programming environments in which the widths of ptrdiff_t, size_t, and wchar_t are no greater than the width of type long. The names of these programming environments can be obtained using the confstr() function or the getconf utility.

The following sections are informative.

#### APPLICATION USAGE

> None.

#### RATIONALE

> None.

#### FUTURE DIRECTIONS

> None.

#### SEE ALSO

> <wchar.h>, <sys/types.h>, the System Interfaces volume of IEEE Std 1003.1-2001, confstr(), the Shell and Utilities volume of IEEE Std 1003.1-2001, getconf

#### CHANGE HISTORY

> First released in Issue 4. Derived from the ANSI C standard.

End of informative text.

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