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Using Generic-Text Mappings 

Microsoft Specific

To simplify code development for various international markets, the Microsoft run-time library provides Microsoft-specific "generic-text" mappings for many data types, routines, and other objects. These mappings are defined in TCHAR.H. You can use these name mappings to write generic code that can be compiled for any of the three kinds of character sets: ASCII (SBCS), MBCS, or Unicode, depending on a manifest constant you define using a #define statement. Generic-text mappings are Microsoft extensions that are not ANSI compatible.

Preprocessor Directives for Generic-Text Mappings
#define Compiled version Example

_UNICODE

Unicode (wide-character)

_tcsrev maps to _wcsrev

_MBCS

Multibyte-character

_tcsrev maps to _mbsrev

None (the default: neither _UNICODE nor _MBCS defined)

SBCS (ASCII)

_tcsrev maps to strrev

For example, the generic-text function _tcsrev, defined in TCHAR.H, maps to mbsrev if MBCS has been defined in your program, or to _wcsrev if _UNICODE has been defined. Otherwise _tcsrev maps to strrev.

The generic-text data type _TCHAR, also defined in TCHAR.H, maps to type char if _MBCS is defined, to type wchar_t if _UNICODE is defined, and to type char if neither constant is defined. Other data type mappings are provided in TCHAR.H for programming convenience, but _TCHAR is the type that is most useful.

Generic-Text Data Type Mappings
Generic-text data type name SBCS (_UNICODE, _MBCS not defined) _MBCS defined _UNICODE defined

_TCHAR

char

char

wchar_t

_TINT

int

int

wint_t

_TSCHAR

signed char

signed char

wchar_t

_TUCHAR

unsigned char

unsigned char

wchar_t

_TXCHAR

char

unsigned char

wchar_t

_T or _TEXT

No effect (removed by preprocessor)

No effect (removed by preprocessor)

L (converts following character or string to its Unicode counterpart)

For a complete list of generic-text mappings of routines, variables, and other objects, see Generic-Text Mappings.

The following code fragments illustrate the use of _TCHAR and _tcsrev for mapping to the MBCS, Unicode, and SBCS models.

_TCHAR *RetVal, *szString;
RetVal = _tcsrev(szString);

If MBCS has been defined, the preprocessor maps the preceding fragment to the following code:

char *RetVal, *szString;
RetVal = _mbsrev(szString);

If _UNICODE has been defined, the preprocessor maps the same fragment to the following code:

wchar_t *RetVal, *szString;
RetVal = _wcsrev(szString);

If neither _MBCS nor _UNICODE has been defined, the preprocessor maps the fragment to single-byte ASCII code, as follows:

char *RetVal, *szString;
RetVal = strrev(szString);

Thus you can write, maintain, and compile a single source code file to run with routines that are specific to any of the three kinds of character sets.

END Microsoft Specific

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