C / C++ / MFC Discussion Boards

Re: L macro

George_George20-Aug-07 17:45

George_George

20-Aug-07 17:45

Hi David,

If it is not a macro, what is it?

regards,
George

Re: L macro

David Crow20-Aug-07 17:51

David Crow

20-Aug-07 17:51

George_George wrote:
If it is not a macro, what is it?

It's simply a prefix to denote wide-string literals.

"A good athlete is the result of a good and worthy opponent." - David Crow

"To have a respect for ourselves guides our morals; to have deference for others governs our manners." - Laurence Sterne

Re: L macro

George_George20-Aug-07 19:19

George_George

20-Aug-07 19:19

Thanks David,

I can understand your point. I mean there should be a technical terminology to call it -- besides the term "prefix". So, if it is not macro, what is it? There is not a technical terminology called "prefix". Smile | :)

regards,
George

Re: L macro

toxcct20-Aug-07 22:11

toxcct

20-Aug-07 22:11

George_George wrote:
If it is not a macro, what is it?

it's an extended keyword of the language

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Re: L macro

George_George20-Aug-07 22:27

George_George

20-Aug-07 22:27

Thanks toxcct,

I want to confirm that keyword L could only be used in C++ and not in C. Right?

regards,
George

Re: L macro

toxcct20-Aug-07 22:37

toxcct

20-Aug-07 22:37

George_George wrote:
want to confirm that keyword L could only be used in C++ and not in C

then why didn't you asked clearly ?
and why do you bother that much ? why is it that important ?
can't you just search the WEB for that easy info ?

BTW, what is it that you vote everybody to '4' ???

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Re: L macro

George_George21-Aug-07 1:05

George_George

21-Aug-07 1:05

Thanks toxcct,

I can not find answer from MSDN so I come here. We could only use L in C++? Can not use in C?

regards,
George

Re: L macro

Iain Clarke, Warrior Programmer20-Aug-07 5:39

Iain Clarke, Warrior Programmer

20-Aug-07 5:39

As has been said, L is not a macro...

char narrow [] = "abc";
TCHAR either [] = _T("abc"); // uses a macro
wchar_t wide [0] = L"abc";

short a = 1L; // will give a warning at least

The last example shows that L is also useful for non-chars, etc.

Iain.

Re: L macro

George_George20-Aug-07 17:13

George_George

20-Aug-07 17:13

Thanks Iain,

You code can not compile in my VS 2003 environment,

This statement

wchar_t* wide [] = L"abc";

error C2075: 'wide' : array initialization needs curly braces

When I change to L("hello"), there is an error from compiler that L is undefined.

regards,
George

Re: L macro

Maxwell Chen20-Aug-07 19:39

Maxwell Chen

20-Aug-07 19:39

George_George wrote:
can not compile in my VS 2003 environment,
This statement
wchar_t* wide [] = L"abc";
error C2075: 'wide' : array initialization needs curly braces
When I change to L("hello"), there is an error from compiler that L is undefined.

The below works fine with Visual Studio 2005.

char narrow [] = "abc";
wchar_t wide [] = L"abc";
short a = 1L; // will give a warning at least

Maxwell Chen

Re: L macro

George_George20-Aug-07 20:17

George_George

20-Aug-07 20:17

Thanks Maxwell,

I have verified that it is ok.

regards,
George

LPCSTR and LPCWSTR

George_George20-Aug-07 4:56

George_George

20-Aug-07 4:56

Hello everyone,

I think when UNICODE or _UNICODE is defined, when using _T, it could convert characters to wide character.

And I also think LPCSTR should be defined to pointer to wide character when UNICODE or _UNICODE is defined, and LPCSTR should be defined to pointer to multibyte character when UNICODE and _UNICODE are not defined.

But it seems I am wrong for all points. Could anyone explain to me why I get such warnings in Visual Studio 2003?

<br />
#include "windows.h"<br />
#include "TCHAR.h"<br />
<br />
#define UNICODE<br />
#define _UNICODE<br />
<br />
int main (int argc, char** argv)<br />
{<br />
        WCHAR* p = _T("hello");<br />
        LPCSTR p1 = p;<br />
        LPCWSTR p2 = p;<br />
}<br />

warning messages,

warning C4133: 'initializing' : incompatible types - from 'char [6]' to 'WCHAR *'
warning C4133: 'initializing' : incompatible types - from 'WCHAR *' to 'LPCSTR'

thanks in advance,
George

Re: LPCSTR and LPCWSTR

David Crow20-Aug-07 5:31

David Crow

20-Aug-07 5:31

The warnings are self-explanatory. With LPCSTR p1 = p, you are trying to assign a WCHAR* (an unsigned short*) to a LPCSTR (a char*), which is incompatible.

"A good athlete is the result of a good and worthy opponent." - David Crow

"To have a respect for ourselves guides our morals; to have deference for others governs our manners." - Laurence Sterne

Re: LPCSTR and LPCWSTR

George_George20-Aug-07 17:30

George_George

20-Aug-07 17:30

Thanks David,

I think we should use LPCTSTR, which is defined to LPCSTR when UNICODE and _UNICODE are not defined, and defined to LPCWSTR when UNICODE or _UNICODE is defined. Right?

regards,
George

Re: LPCSTR and LPCWSTR

David Crow20-Aug-07 17:45

David Crow

20-Aug-07 17:45

George_George wrote:
Right?

Yes.

"A good athlete is the result of a good and worthy opponent." - David Crow

"To have a respect for ourselves guides our morals; to have deference for others governs our manners." - Laurence Sterne

Re: LPCSTR and LPCWSTR

George_George20-Aug-07 17:47

George_George

20-Aug-07 17:47

Hi David,

A further question,

why the statement has warning message when UNICODE is defined (you can find it from my sample in question)?

WCHAR* p = _T("hello");

warning C4133: 'initializing' : incompatible types - from 'char [6]' to 'WCHAR *'

regards,
George

Re: LPCSTR and LPCWSTR

David Crow21-Aug-07 3:13

David Crow

21-Aug-07 3:13

I get this error when Unicode is not defined. If Unicode is defined, it compiles fine.

"A good athlete is the result of a good and worthy opponent." - David Crow

"To have a respect for ourselves guides our morals; to have deference for others governs our manners." - Laurence Sterne

Re: LPCSTR and LPCWSTR

George_George21-Aug-07 3:17

George_George

21-Aug-07 3:17

Thanks David,

I have tried that your method works!

regards,
George

Re: LPCSTR and LPCWSTR

Iain Clarke, Warrior Programmer20-Aug-07 5:41

Iain Clarke, Warrior Programmer

20-Aug-07 5:41

I'm not quite sure why you asked *almost* the same question 20 minutes later...

LPCSTR <-- narrow
LPCWSTR <-- wide
LPCTSTR <-- depends on UNICODE (or _UNICODE, I forget which)

Iain.

Re: LPCSTR and LPCWSTR

George_George20-Aug-07 17:26

George_George

20-Aug-07 17:26

Good reply, Iain!

regards,
George

Re: LPCSTR and LPCWSTR

George_George20-Aug-07 17:36

George_George

20-Aug-07 17:36

Hi Iain,

A further question,

why the statement has warning message when UNICODE is defined (you can find it from my sample in question)?

WCHAR* p = _T("hello");

warning C4133: 'initializing' : incompatible types - from 'char [6]' to 'WCHAR *'

regards,
George

Re: LPCSTR and LPCWSTR

Iain Clarke, Warrior Programmer21-Aug-07 0:02

Iain Clarke, Warrior Programmer

21-Aug-07 0:02

No idea, I don't use WCHAR. You'd have to look at the headers to see what's going on.

But I'd change the _T("Hello") to L"Hello". If *that* works, then _T is converting to ascii, and you haven't defined _UNICODE or UNICODE (I can never remember which is which, but one is for C, and one for Win32).

The reason you bother with _T is so that the code will be either ascii or unicode, depending on the defines. In which case, you should use TCHAR, as this varies similarly. If you're hard wiring for unicode, then you can write:

wchar_t *p = L"Hello";

instead.

You had a similar issue in another question to to with LPSTR/LPTSTR/LPWSTR. You need to make up your mind whether you're being ascii, dependent on defines, or full on unicode.

This mixing of hard wired and dependent-on-defines code is going to give you errors in both directions...

Iain

Re: LPCSTR and LPCWSTR

George_George21-Aug-07 1:24

George_George

21-Aug-07 1:24

Thanks Iain,

Iain Clarke wrote:
one is for C, and one for Win32

What do you mean one is for C and one for Win32? You mean _UNICODE for C? UNICODE for Win32? Could you provide more information please?

regards,
George

Re: LPCSTR and LPCWSTR

Iain Clarke, Warrior Programmer21-Aug-07 3:29

Iain Clarke, Warrior Programmer

21-Aug-07 3:29

When I said I couldn't remember which one is which, I meant it. It's not all that hard to search in MSDN for the definitions, or use Visual C++ to search for the #ifdef's in the header files to see where they crop up. Basically, if I need either of them, I need both.

It's one thing for us to be helpful, but you gotta do *some* of the work yourself!

Iain.

Re: LPCSTR and LPCWSTR

George_George21-Aug-07 5:28

George_George

21-Aug-07 5:28

Thanks for your advice, Iain!

regards,
George

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