Re: BSTR Problem - C / C++ / MFC Discussion Boards

Re: Error at compiling virtual function call in constructor

Nemanja Trifunovic10-Mar-04 6:23

Nemanja Trifunovic

10-Mar-04 6:23

Welcome back, Tomasz Cool | :cool:

Re: Error at compiling virtual function call in constructor

Tomasz Sowinski11-Mar-04 2:47

Tomasz Sowinski

11-Mar-04 2:47

Thanks, Nemanja. I was just passing by and had a look at good ol' VC board Smile | :)

Tomasz Sowinski -- http://www.shooltz.com

InvertRect

Anthony988710-Mar-04 3:50

Anthony9887

10-Mar-04 3:50

Is there a way to change the black highlight to a different colour?

Thanks

BSTR Problem

Nick Parker10-Mar-04 3:34

Nick Parker

10-Mar-04 3:34

I have a function receiving a BSTR within an ATL project. I have placed a break point in the C++ code a added a watch to the incoming variable. When I create an instance of it within VB (don't start) to test it and pass it a directory path, I am only getting the first letter of the string that should be passed in. Any clues?

STDMETHODIMP CMoses::SetArguments(BSTR dir)
{
	AFX_MANAGE_STATE(AfxGetStaticModuleState())
	::AfxMessageBox((LPCTSTR)dir, MB_OK); // for debugging purposes.
	CString val;
	val = (LPCTSTR)dir;
	::AfxMessageBox(val, MB_OK);  // for debugging purposes.
	root.SetArguments(val);
	return S_OK;
}

- Nick Parker
My Blog

Re: BSTR Problem

David Crow10-Mar-04 3:39

David Crow

10-Mar-04 3:39

By default, strings in the Watch window use the ,s symbol. You need to use ,su for Unicode strings. So, if you have a breakpoint in the SetArguments() method, you should have dir,su in the Watch window.

"The pointy end goes in the other man." - Antonio Banderas (Zorro, 1998)

Re: BSTR Problem

Nick Parker10-Mar-04 3:49

Nick Parker

10-Mar-04 3:49

David, thank you very much. Smile | :)

- Nick Parker
My Blog

Re: BSTR Problem

toxcct10-Mar-04 3:40

toxcct

10-Mar-04 3:40

that's very clear !!

you watch a variable that is a pointer...
what you want from this pointer is to show the string containig the caracters at th folowing addresses, until it encounters a '\0'... that is surely what happened. The second caracter of your string is very certainly a '\0'... watch this !

TOXCCT >>> GEII power

Re: BSTR Problem

Michael Dunn10-Mar-04 4:03

Michael Dunn

10-Mar-04 4:03

Nick Parker wrote:
val = (LPCTSTR)dir;

That's the bug. A BSTR points to a Unicode string, not a TCHAR string. Change it to:

val = (LPCWSTR)dir;

--Mike--
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Re: BSTR Problem

Nick Parker10-Mar-04 4:07

Nick Parker

10-Mar-04 4:07

Thank Mike, I just saw that too. The value has to be passed to a function that accepts a LPCTSTR. Should I expect any problems passing a CString to it instead (i.e.; val being of type CString)?

- Nick Parker
My Blog

Re: BSTR Problem

Prakash Nadar10-Mar-04 5:09

Prakash Nadar

10-Mar-04 5:09

Is it ok to assign BSTR to CString under non UNICODE compilation?

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Re: BSTR Problem

Michael Dunn10-Mar-04 6:35

Michael Dunn

10-Mar-04 6:35

Yes because CString has constructors that take LPCSTR and LPCWSTR.

--Mike--
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Problem when adding two wave files

Member 95034310-Mar-04 3:26

Member 950343

10-Mar-04 3:26

hello!

i wrote a program to combine two wave files into one.
for that i read wave file using CFile class according to
the file format.i am reading samples into vector<int>
variables.i am combininig two vectors and writing to the
file according to the wav format.its playing as three waves.
that i mean each wave as two.

if u know to solve pls help me!

what does (CeditStr *) in (CeditStr *)Variable.funcition do??

BrockVnm10-Mar-04 3:20

BrockVnm

10-Mar-04 3:20

I have a real basic question. I know this is something really easy but I am not totally sure what it means. I am learning mfc and in my book I see this:

pES = (CEditStr*)mLines.GetAt(mPosActive);

What does the (CEditStr *) mean in front of the variable? Does it have to be there?? I am not sure when I would need to use it. If anyone could explain it to me that would be great......Thanks!!!

Confused | :confused:

Re: what does (CeditStr *) in (CeditStr *)Variable.funcition do??

toxcct10-Mar-04 3:27

toxcct

10-Mar-04 3:27

that code is a cast. It means that the address recorded into the pointer mLines.GetAt(mPosActive) will be interpreted as a CEditstr pointer.
If that pointer already have this type, the cast is not needed, but you can use it for your code to be "readable". Of course, if your pointer is in another type, you must explicit the cast this way...

Wink | ;)

TOXCCT >>> GEII power

Re: what does (CeditStr *) in (CeditStr *)Variable.funcition do??

David Crow10-Mar-04 3:28

David Crow

10-Mar-04 3:28

It is casting the return value of GetAt() to a CEditStr*.

"The pointy end goes in the other man." - Antonio Banderas (Zorro, 1998)

Re: what does (CeditStr *) in (CeditStr *)Variable.funcition do??

BrockVnm10-Mar-04 4:28

BrockVnm

10-Mar-04 4:28

So the GetAt functions returns a pointer of CEditStr. Perfect!

thank you everyone!! Big Grin | :-D

Re: what does (CeditStr *) in (CeditStr *)Variable.funcition do??

David Crow10-Mar-04 4:43

David Crow

10-Mar-04 4:43

If that's the case, then the cast in the code snippet you provided is redundant.

"The pointy end goes in the other man." - Antonio Banderas (Zorro, 1998)

Re: what does (CeditStr *) in (CeditStr *)Variable.funcition do??

BrockVnm10-Mar-04 4:56

BrockVnm

10-Mar-04 4:56

So when would I use casting? How would the code snippet be redundant?

Re: what does (CeditStr *) in (CeditStr *)Variable.funcition do??

David Crow10-Mar-04 5:15

David Crow

10-Mar-04 5:15

BrockVnm wrote:
So when would I use casting?

When an object needs to be coerced into acting like another type. Casting does not convert, is just represents.

BrockVnm wrote:
How would the code snippet be redundant?

The cast here is redundant since the array is holding CString* types and that's how we want to use it.

CArray< CString *, CString *> arr;
CString *p = (CString *) arr.GetAt(5);

The cast here is necessary because the array is holding CWnd* types, but we want to use one of them as a CEdit* type

CArray< CWnd *, CWnd *> arr;
CEdit *p = (CEdit *) arr.GetAt(5);

A simpler example might be:

double dRate = 1.997;
double d1 = (double) dRate; // not necessary
int nWhole = (int) dRate;   // necessary, since we only want to operate on the 'whole' part of the number

"The pointy end goes in the other man." - Antonio Banderas (Zorro, 1998)

Re: what does (CeditStr *) in (CeditStr *)Variable.funcition do??

Prakash Nadar10-Mar-04 6:27

Prakash Nadar

10-Mar-04 6:27

My oh My what a lovely answer!!!
But i guess someone has downvoted you, i will give you a 5er.
Anyways there is one thing i would like to add.
Casting has different effect on pointers and native data types.

DavidCrow wrote:
CEdit *p = (CEdit *) arr.GetAt(5);
as you said the pointer representation is modified.

and on native data types.

DavidCrow wrote:
int nWhole = (int) dRate;

is converting the data type.

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typedef struct <-> struct

Konrad Windszus10-Mar-04 3:03

Konrad Windszus

10-Mar-04 3:03

What's the difference between

typedef struct _MYSTRUCT {<br />
 int nValue;<br />
 DWORD dwValue2;<br />
}MYSTRUCT;

and

struct MYSTRUCT {<br />
 int nValue;<br />
 DWORD dwValue2;<br />
};

With each of them I can instantiate variables of type MYSTRUCT like:
MYSTRUCT myStruct;

And I doesn't need the old C style:
struct MYSTRUCT myStruct;

So why should I use typedef combined with struct. Are there any advantages or disadvantages.
Thanks for any comment.
Konrad

Re: typedef struct <-> struct

toxcct10-Mar-04 3:11

toxcct

10-Mar-04 3:11

you're not obiged to...
the reason some code use this, it is because C don't allow to use types without the struct identifier, or when your struct is typedefed...
In C++, it is only a portability reason...

TOXCCT >>> GEII power

Re: typedef struct <-> struct

Robert A. T. Káldy11-Mar-04 1:44

Robert A. T. Káldy

11-Mar-04 1:44

In a good old C, you can use structures only with the keyword struct. In C++, the only advantage of using typedef is, that you write the struct name with one word Smile | :)

. In your example, MYSTRUCT is an alias to struct _MYSTRUCT.

Robert-Antonio

"Czech Railways discovered, that in case of disaster the most damaged wagons
were the first and the last. So they decided to create trains without them."

Problem with popup menus

amit sebiz10-Mar-04 1:34

amit sebiz

10-Mar-04 1:34

hi eerybody,
i am having a problem with popup menus.
The handlers associated with the menus are not called when i click on the menuitem in release mode but things work fine with debug mode.

Can anyone help.

thnx in advance,
Amit

Re: Problem with popup menus

Vahid Kazemi10-Mar-04 6:03

Vahid Kazemi

10-Mar-04 6:03

in debug mode, compiler do some more operations such as setting default variable values to 0 and undefined pointers to NULL. this may cause a wrong code to be run correctly, so check your code again and look for these types of errors.

Vahid Kazemi (http://www.gameprogrammer.org)

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