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Unicode Programming Summary

  • Article

To take advantage of the MFC and C run-time support for Unicode, you need to:

  • Define _UNICODE.

    Define the symbol _UNICODE before you build your program.

  • Specify entry point.

    On the Advanced page of the Linker folder in the project's Property Pages dialog box, set the Entry Point symbol to wWinMainCRTStartup.

  • Use portable run-time functions and types.

    Use the proper C run-time functions for Unicode string handling. You can use the wcs family of functions, but you might prefer the fully portable (internationally enabled) _TCHAR macros. These macros are all prefixed with _tcs; they substitute, one for one, for the str family of functions. These functions are described in detail in the Internationalization section of the Run-Time Library Reference. For more information, see Generic-Text Mappings in tchar.h.

    Use _TCHAR and the related portable data types described in Support for Unicode.

  • Handle literal strings properly.

    The Visual C++ compiler interprets a literal string coded as:

    L"this is a literal string"

    to mean a string of Unicode characters. You can use the same prefix for literal characters. Use the _T macro to code literal strings generically, so they compile as Unicode strings under Unicode or as ANSI strings (including MBCS) without Unicode. For example, instead of:

    pWnd->SetWindowText( "Hello" );

    use:

    pWnd->SetWindowText( _T("Hello") );

    With _UNICODE defined, _T translates the literal string to the L-prefixed form; otherwise, _T translates the string without the L prefix.

    Tip

    The _T macro is identical to the _TEXT macro.

  • Be careful passing string lengths to functions.

    Some functions want the number of characters in a string; others want the number of bytes. For example, if _UNICODE is defined, the following call to a CArchive object will not work (str is a CString):

    archive.Write( str, str.GetLength( ) );    // invalid

    In a Unicode application, the length gives you the number of characters but not the correct number of bytes, because each character is 2 bytes wide. Instead, you must use:

    archive.Write( str, str.GetLength( ) * sizeof( _TCHAR ) );    // valid

    which specifies the correct number of bytes to write.

    However, MFC member functions that are character-oriented, rather than byte-oriented, work without this extra coding:

    pDC->TextOut( str, str.GetLength( ) );

    CDC::TextOut takes a number of characters, not a number of bytes.

  • Use fopen_s, _wfopen_s to open Unicode files.

To summarize, MFC and the run-time library provide the following support for Unicode programming:

  • Except for database class member functions, all MFC functions are Unicode-enabled, including CString. CString also provides Unicode/ANSI conversion functions.

  • The run-time library supplies Unicode versions of all string-handling functions. (The run-time library also supplies portable versions suitable for Unicode or for MBCS. These are the _tcs macros.)

  • tchar.h supplies portable data types and the _T macro for translating literal strings and characters. For more information, see Generic-Text Mappings in tchar.h.

  • The run-time library provides a wide-character version of main. Use wmain to make your application Unicode-aware.

See also

Support for Unicode