CString -> LPCWSTR

[Guest]

Hi,

Any one knows how to convert CString to LPCWSTR?

Please advice, thanks!
-P

 

[Antti Keskinen]

Hello !

LPCWSTR is a pointer to a constant wchar_t string.

Using Visual Studio .NET 2003 this is an easy task. In the ATL-MFC version
7, a set of conversion macros are provided to simplify the process. So, in
order to convert it, the following command would do it

CT2CW( (LPCTSTR) MyStringObj );

This would return a constant pointer to a wchar_t string (LPCWSTR). Note
that if you wish to save this, reserve memory for a wchar_t string and then
use string copying to copy from the return value of this macro into the new
string. For further information, see MSDN with topic "ATL and MFC String
Conversion Macros". Or use keyword search with the macro name.

If you don't have .NET 2003, you can still do the conversion, but must use
the old-style macros, which are somewhat less sophisticated (read: might
contain bugs). The calling convention of this would be:

T2W( (LPCTSTR) MyStringObj );

Hope this helps !

-Antti Keskinen

 

[Guest]

Cool, thanks for the info!

-P

Hello !

LPCWSTR is a pointer to a constant wchar_t string.

Using Visual Studio .NET 2003 this is an easy task. In the ATL-MFC version
7, a set of conversion macros are provided to simplify the process. So, in
order to convert it, the following command would do it

CT2CW( (LPCTSTR) MyStringObj );

This would return a constant pointer to a wchar_t string (LPCWSTR). Note
that if you wish to save this, reserve memory for a wchar_t string and then
use string copying to copy from the return value of this macro into the new
string. For further information, see MSDN with topic "ATL and MFC String
Conversion Macros". Or use keyword search with the macro name.

If you don't have .NET 2003, you can still do the conversion, but must use
the old-style macros, which are somewhat less sophisticated (read: might
contain bugs). The calling convention of this would be:

T2W( (LPCTSTR) MyStringObj );

Hope this helps !

-Antti Keskinen

 

[Antti Keskinen]

Hello !

This is a simple process. Visual Studio .NET (and ATL-MFC version 7)
supports new conversion macros with the following syntax:

C<sourcetype>2<constant><destination type><ex>

In which, <sourcetype> is T for generic text, A for ANSI, W for wchar_t
types and OLE for COM/BSTR strings (wchar_t normally). <constant> is a 'C'
if the destination pointer must be a constant one, and <destination type> is
the target type, again from the above list of source types. <ex> is 'EX' if
the target string's length needs to be defined in the template.

Thus, converting from CString to LPCWSTR is as simple as this:

CT2CW( (LPCTSTR) MyStringObj );

You could read this like "convert generic type to constant wchar_t".
Creating sentences like this helps you quickly understand how to build the
macro to support a specific conversion. The conversion is actually a class
that uses a certain piece of memory to hold a copy of the string in the
appropriate format. Thus, when the class goes out-of-scope, the new string
is freed. Generally, you should not rely on this, but use the conversion
macro as a parameter to a function or source of a string copying routine.
This allows you to create local strings that last just as long as you want
them to. The conversion should be used with "in-place conversion from one
pointer type to other" -mantra.

Following this idea, this piece of code is BAD, DO NOT USE:

LPCWSTR lpwStr = CT2CW( (LPCTSTR) StringObj );

Instead, something like this is much better, if the string is no longer than
20 characters

wchar_t string[20];
wcscpy( string, CT2CW( (LPCTSTR) StringObj );

If you don't have ATL-MFC v7, you can use the old-style conversion macros,
such as

T2CW( (LPCTSTR) StringObj );

Note that these macros MUST be used in the above mentioned string copying
way. Using them otherwise will have undesirable results.

See MSDN with "ATL and MFC String Conversion Macros" for more information on
the conversion routines. Same topic will cover the old-style conversion
macros.

-Antti Keskinen

 

[Gabest]

I've never understood why people rely on these macros instead of doing
things like CStringW(s). Why those ugly hidden stack variables are better
than letting the compiler generate the temporaries automatically?

 

[Antti Keskinen]

Guess it's just a matter of preference.

I generally write all my production code with Unicode enabled. This ensures
that the program will work on every Windows operating system, no matter
where it's ran. It makes programming and string manipulation a bit more
difficult (two bytes instead of one for each character), but after getting
used to, it's quite a breeze, while ensuring compatibility.

-Antti Keskinen