C Library -

The stddef.h header defines various variable types and macros. Many of these definitions also appear in other headers.

Library Variables

Following are the variable types defined in the header stddef.h −

S.N.	Variable & Description
1	ptrdiff_t This is the signed integral type and is the result of subtracting two pointers.
2	size_t This is the unsigned integral type and is the result of the sizeof keyword.
3	wchar_t This is an integral type of the size of a wide character constant.

Library Macros

Following are the macros defined in the header stddef.h −

S.N.	Macro & Description
1	NULL This macro is the value of a null pointer constant.
2	offsetof(type, member-designator) This results in a constant integer of type size_t which is the offset in bytes of a structure member from the beginning of the structure. The member is given by member-designator, and the name of the structure is given in type.