21 Language support library [language.support]

21.2 Common definitions [support.types]

21.2.1 Header <cstddef> synopsis [cstddef.syn]

namespace std {
  using ptrdiff_t = see below;
  using size_t = see below;
  using max_align_t = see below;
  using nullptr_t = decltype(nullptr);

  enum class byte : unsigned char {};

  // [support.types.byteops], byte type operations
  template <class IntType>
    constexpr byte& operator<<=(byte& b, IntType shift) noexcept;
  template <class IntType>
    constexpr byte operator<<(byte b, IntType shift) noexcept;
  template <class IntType>
    constexpr byte& operator>>=(byte& b, IntType shift) noexcept;
  template <class IntType>
    constexpr byte operator>>(byte b, IntType shift) noexcept;
  constexpr byte& operator|=(byte& l, byte r) noexcept;
  constexpr byte operator|(byte l, byte r) noexcept;
  constexpr byte& operator&=(byte& l, byte r) noexcept;
  constexpr byte operator&(byte l, byte r) noexcept;
  constexpr byte& operator^=(byte& l, byte r) noexcept;
  constexpr byte operator^(byte l, byte r) noexcept;
  constexpr byte operator~(byte b) noexcept;
  template <class IntType>
    constexpr IntType to_integer(byte b) noexcept;
}

#define NULL see below
#define offsetof(P, D) see below

The contents and meaning of the header <cstddef> are the same as the C standard library header <stddef.h>, except that it does not declare the type wchar_t, that it also declares the type byte and its associated operations ([support.types.byteops]), and as noted in [support.types.nullptr] and [support.types.layout].