Unicode Programming Summary
To take advantage of the MFC and C run-time support for Unicode, you need to:
Define the symbol
_UNICODEbefore 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
Use portable run-time functions and types.
Use the proper C run-time functions for Unicode string handling. You can use the
wcsfamily of functions, but you might prefer the fully portable (internationally enabled)
_TCHARmacros. These macros are all prefixed with
_tcs; they substitute, one for one, for the
strfamily 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.
_TCHARand 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
_Tmacro 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" );
pWnd->SetWindowText( _T("Hello") );
_Ttranslates the literal string to the L-prefixed form; otherwise,
_Ttranslates the string without the L prefix.
_Tmacro is identical to the
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
_UNICODEis defined, the following call to a
CArchiveobject will not work (
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::TextOuttakes 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
CStringalso 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
tchar.h supplies portable data types and the
_Tmacro 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
wmainto make your application Unicode-aware.
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