ANSI-C Standard Types 'size_t', 'wchar_t' and 'ptrdiff

ANSI provides some standard defines in stddef.h to deal with the implementation of defined object sizes.

The following listing shows the part of the contents of stdtypes.h (included from stddef.h).

Listing: Type Definitions of ANSI-C Standard Types

/* size_t: defines the maximum object size type */ 
 #if defined(__SIZE_T_IS_UCHAR__) 
 typedef unsigned char size_t; 
 #elif defined(__SIZE_T_IS_USHORT__) 
 typedef unsigned short size_t; 
 #elif defined(__SIZE_T_IS_UINT__) 
 typedef unsigned int size_t; 
 #elif defined(__SIZE_T_IS_ULONG__) 
 typedef unsigned long size_t; 
 #else 
 #error "illegal size_t type" 
 #endif 
/* ptrdiff_t: defines the maximum pointer difference type */ 
 #if defined(__PTRDIFF_T_IS_CHAR__) 
 typedef signed char ptrdiff_t; 
 #elif defined(__PTRDIFF_T_IS_SHORT__) 
 typedef signed short ptrdiff_t; 
 #elif defined(__PTRDIFF_T_IS_INT__) 
 typedef signed int ptrdiff_t; 
 #elif defined(__PTRDIFF_T_IS_LONG__) 
 typedef signed long ptrdiff_t; 
 #else 
 #error "illegal ptrdiff_t type" 
 #endif 
/* wchar_t: defines the type of wide character */ 
#if defined(__WCHAR_T_IS_UCHAR__) 
 typedef unsigned char wchar_t; 
#elif defined(__WCHAR_T_IS_USHORT__) 
 typedef unsigned short wchar_t; 
#elif defined(__WCHAR_T_IS_UINT__) 
 typedef unsigned int wchar_t; 
#elif defined(__WCHAR_T_IS_ULONG__) 
 typedef unsigned long wchar_t; 
#else 
 #error "illegal wchar_t type" 
#endif

The following table lists defines that deal with other possible implementations:

Table 1. Defines for Other Implementations
Macro	Description
`__SIZE_T_IS_UCHAR__`	Defined if the Compiler expects `size_t` in `stddef.h` to be `unsigned char`.
`__SIZE_T_IS_USHORT__`	Defined if the Compiler expects `size_t` in `stddef.h` to be `unsigned short`.
`__SIZE_T_IS_UINT__`	Defined if the Compiler expects `size_t` in `stddef.h` to be `unsigned int`.
`__SIZE_T_IS_ULONG__`	Defined if the Compiler expects `size_t` in `stddef.h` to be `unsigned long`.
`__WCHAR_T_IS_UCHAR__`	Defined if the Compiler expects `wchar_t` in `stddef.h` to be `unsigned char`.
`__WCHAR_T_IS_USHORT__`	Defined if the Compiler expects `wchar_t` in `stddef.h` to be `unsigned short`.
`__WCHAR_T_IS_UINT__`	Defined if the Compiler expects `wchar_t` in `stddef.h` to be `unsignedint`.
`__WCHAR_T_IS_ULONG__`	Defined if the Compiler expects `wchar_t` in `stddef.h` to be `unsigned long`.
`__PTRDIFF_T_IS_CHAR__`	Defined if the Compiler expects `ptrdiff_t` in `stddef.h` to be `char`.
`__PTRDIFF_T_IS_SHORT__`	Defined if the Compiler expects `ptrdiff_t` in `stddef.h` to be `short`.
`__PTRDIFF_T_IS_INT__`	Defined if the Compiler expects `ptrdiff_t` in `stddef.h` to be `int`.
`__PTRDIFF_T_IS_LONG__`	Defined if the Compiler expects `ptrdiff_t` in `stddef.h` to be `long`.

The following tables show the default settings of the ANSI-C Compiler size_t and ptrdiff_t standard types.

ANSI-C Standard Types 'size_t', 'wchar_t' and 'ptrdiff_t' Defines