Unicode Programming Summary

Visual C++ Concepts: Adding Functionality

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.
In the Output 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 may 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, since each character is two 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.

To summarize, MFC and the run-time library provide the following support for Unicode programming under Windows 2000:

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. 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