Support for Multibyte Character Sets (MBCS)

Unicode TasksMultibyte Character Set (MBCS) Tasks

For platforms used in markets whose languages use large character sets, the best alternative to Unicode is MBCS. MFC supports MBCS by using “internationalizable” data types and C run-time functions. You should do the same in your code.

Under MBCS, characters are encoded in either one or two bytes. In two-byte characters, the first, or “lead-byte,” signals that both it and the following byte are to be interpreted as one character. The first byte comes from a range of codes reserved for use as lead bytes. Which ranges of bytes can be lead bytes depends on the code page in use. For example, Japanese code page 932 uses the range 0x81 through 0x9F as lead bytes, but Korean code page 949 uses a different range.

Consider all of the following in your MBCS programming:

MBCS characters in the environment

MBCS characters can appear in strings such as file and directory names.

Editing operations

Editing operations in MBCS applications should operate on characters, not bytes. The caret should not split a character, the RIGHT ARROW key should move right one character, and so on. Delete should delete a character; Undo should reinsert it.

String handling

In an application that uses MBCS, string handling poses special problems. Characters of both widths are mixed in a single string; therefore you must remember to check for lead bytes.

Run-time library support

The C run-time library and MFC support single-byte, MBCS, and Unicode programming. Single-byte strings are processed with the str family of run-time functions, MBCS strings are processed with corresponding _mbs functions, and Unicode strings are processed with corresponding wcs functions. MFC class member function implementations use portable run-time functions that map, under the right circumstances, to the normal str family of functions, the MBCS functions, or the Unicode functions, as described in “MBCS/Unicode portability.”

MBCS/Unicode portability

Using the header file TCHAR.H, you can build single-byte, MBCS, and Unicode applications from the same sources. TCHAR.H defines macros prefixed with _tcs , which map to str, _mbs, or wcs functions, as appropriate. To build MBCS, define the symbol _MBCS. To build Unicode, define the symbol _UNICODE. By default, _MBCS is defined for MFC applications. For more information, see Generic-Text Mappings in TCHAR.H.

Note   Behavior is undefined if you define both _UNICODE and _MBCS.

The MBCTYPE.H and MBSTRING.H header files define MBCS-specific functions and macros, which you may need in some cases. For example, _ismbblead tells you whether a specific byte in a string is a lead byte.

See Also   MBCS Support in Visual C++