The <stddef.h> header defines the following macros:
Null pointer constant.
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 defines the following types:
Signed integer type of the result of subtracting two pointers.
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.
Unsigned integer type of the result of the sizeof operator.
The implementation supports 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(3C) function or the getconf (1) utility.
See attributes(5) for descriptions of the following attributes: