Stddef.h

stddef.h is a header file in the standard library of the C programming language which defines the macro NULL and the types ptrdiff_t, wchar_t, and size_t.

Inclusion

In C, one includes the header file "stddef.h", as in:
#include /* ... */

In C++, one includes the header file "cstddef", as in:
#include // ...

Namespace

The header file "stddef.h" places its definitions in the global scope; the header file "cstddef" places size_t and ptrdiff_t in namespace "std".

NULL

A macro that expands to a null pointer constant.It may be defined as ((void*)0), 0 or 0L depending on the compiler and the language.

Type size_t

The type size_t represents the appropriate type for representing the size of objects of memory areas, and for use in dereferencing the elements of an array. It has an implementation-dependent size; usually, it has a 32-bit representation on 32-bit systems and a 64-bit representation on 64-bit systems. It is unsigned. It has a signed variation, ssize_t, defined in the UNIX header file, "unistd.h".

Type wchar_t

An implementation-specific "wide character" type, which is predefined in the C++ programming language but requires the header "stddef.h" or "wchar.h" in the C programming language.

Type ptrdiff_t

The type ptrdiff_t is a type that can hold the result of subtracting two pointers. The underlying type of ptrdiff_t varies from implementation to implementation.

External references

* [http://www.opengroup.org/pubs/online/7908799/xsh/stddef.h.html stddef.h] on The Open Group
* [http://www.cplusplus.com/reference/clibrary/cstddef/ stddef.h] on CPlusPlus.com
* [http://msdn2.microsoft.com/en-us/library/2b6eh9x3(VS.80).aspx cstddef] on MSDN