stddef.h - standard type definitions
[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 POSIX.1-2017 defers to the ISO C standard.
The <stddef.h> header shall define the following macros:
- Null pointer constant. [CX] The macro shall expand to an integer constant expression with the value 0 cast to type void *.
- 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:
- Signed integer type of the result of subtracting two pointers.
- Integer type whose range of values can represent distinct codes for all members of the largest extended character set specified among the supported locales; the null character shall have the code value zero. Each member of the basic character set shall have a code value equal to its value when used as the lone character in an integer character constant if an implementation does not define __STDC_MB_MIGHT_NEQ_WC__.
- 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 ISO C standard does not require the NULL macro to include the cast to type void * and specifies that the NULL macro be implementation-defined. POSIX.1-2017 requires the cast and therefore need not be implementation-defined.
First released in Issue 4. Derived from the ANSI C standard.
This reference page is clarified with respect to macros and symbolic constants.
SD5-XBD-ERN-53 is applied, updating the definition of wchar_t to align with ISO/IEC 9899:1999 standard, Technical Corrigendum 3.
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