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Support for Multibyte Character Sets (MBCSs)

Multibyte character sets (MBCSs) are an older approach to the need to support character sets, like Japanese and Chinese, that cannot be represented in a single byte. If you are doing new development, you should use Unicode for all text strings except perhaps system strings that are not seen by end users. MBCS is a legacy technology and is not recommended for new development.

The most common MBCS implementation is double-byte character sets (DBCSs). Visual C++ in general, and MFC in particular, is fully enabled for DBCS.

For samples, see the MFC source code files.

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 1 or 2 bytes. In 2-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 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 tchar.h header file, 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, _UNICODE is defined for MFC applications. For more information, see Generic-Text Mappings in tchar.h.


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 might need in some cases. For example, _ismbblead tells you whether a specific byte in a string is a lead byte.

For international portability, code your program with Unicode or multibyte character sets (MBCSs).

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See also

Text and Strings
MBCS Support in Visual C++