Cast CString to ANSI string in UNICODE projects

Quick Answer: use an intermediate CStringA.

• Normally, this is not something that should be done.
• It is technically unreliable, unless you can guarantee that the source CString to be converted does not contain any 2-byte characters.
• This will work fine if you are using the English language without any special 2-byte symbols or accented letters.
• This article is for educational use, and explains how it can easily be done, without relying on the USES_CONVERSION macro with W2A, or ridiculous WideCharToMultiByte API functions.
• If you are using a language that actually requires Unicode (Asian languages, etc), or if the CString contains any 2-byte character, this cannot be done. This is because there is no ANSI equivalent of any 2-byte character.
• It is the responsibility of the programmer to ensure that the CString does not contain any 2-byte characters.

Use intermediate CStringA:

• Recommended, simple, easy, effective, almost impossible to use improperly.
• This is only reliable if the CString does not contain any 2-byte characters.

CString LastNameW( L"Smith" );
CStringA LastNameA( LastNameW );
FunctionForAnsi( (LPCSTR)LastNameA );

• Or an even simpler example:

CString LastNameW( L"Smith" );
FunctionForAnsi( (LPCSTR)CStringA( LastNameW ) );

Here are some other ways that either do not work or are not recommended. I list them here to document things to avoid. What not to do.

WideCharToMultiByte API function:

• Not recommended, too much code to write, test, debug.

CString LastNameW( L"Smith" );
int nLen = WideCharToMultiByte( CP_ACP, 0, (LPCWSTR)LastNameW, -1, NULL, NULL );
LPSTR lpszA = new CHAR[nLen];
WideCharToMultiByte( CP_ACP, 0, (LPCWSTR)LastNameW, -1, lpszA, nLen );
FunctionForAnsi( lpszA );
delete[] lpszA; // free the string

W2A ATL 3.0 macros:

• Not recommended, not safe inside loops.

USES_CONVERSION;
CString LastNameW( L"Smith" );
FunctionForAnsi( W2A( (LPCWSTR)LastNameW ) );

CW2A ATL 7.0 conversion template classes:

• Not recommended, strict rules to follow for proper usage, too easy to use improperly.

CW2A: correct usage:

CString LastNameW( L"Smith" );
CW2A pszA( (LPCWSTR)LastNameW ); // this is the right way
FunctionForAnsi( pszA );

CW2A: improper usage, do not do this

CString LastNameW( L"Smith" );
FunctionForAnsi( CW2A( (LPCWSTR)LastNameW ) ); // improper usage, do not do this

CW2A: improper usage, do not do this

CString LastNameW( L"Smith" );
LPCSTR pszA = CW2A( (LPCWSTR)LastNameW ); // improper usage, do not do this
FunctionForAnsi( pszA );

(LPCSTR)(LPCTSTR) cast:

• Does not work.
• You cannot simply use (LPCSTR)(LPCTSTR) to cast a CString to LPCSTR in Unicode projects.
• It does compile, but it does not properly convert the CStringW to an LPCSTR.
• The resulting string will either be 0 or 1 length, or filled with garbage characters of unknown length, because the cast just changes the pointer type without any conversion.
• You end up with a CHAR* pointing to a WCHAR array, a very bad thing.

CString LastName( L"Smith" );
FunctionForAnsi( (LPCSTR)(LPCTSTR)LastName ); // does not work

REF:

ATL String: What’s wrong with the USES_CONVERSION macros? How to avoid using them?

Using MFC MBCS/Unicode Conversion Macros

ATL and MFC String Conversion Macros