C / C++ / MFC

Jim Howard22-Jun-01 6:02

Jim Howard

22-Jun-01 6:02

They almost certainly are not identical. VB uses "BSTR"s, which store a lenght value and then an array of character data, while C/C++ generally use null terminated character arrays as strings. It's a pain in the rear to go back and forth, but not hard once you grock the two concepts.

For a good overview of different flavors of strings, see the string article at:

http://www.pgh.net/~newcomer/mvp_tips.htm

Jim

John Uhlenbrock22-Jun-01 6:41

John Uhlenbrock

22-Jun-01 6:41

Thanks, thats a good site, it helps. I am still looking for a way to display these strings in bit or hex form.

Jim Howard22-Jun-01 7:08

Jim Howard

22-Jun-01 7:08

We just had this discussion over at microsoft.public.vc.mfc

Here is one example from that discussion:

<br />
CString strBytes("ff10ab");<br />
char buffer[2];//buffer to hold each digit of strBytes for conversion<br />
buffer[0] = 0; //null terminator required <br />
int digit;<br />
for(int i=0;i<strBytes.GetLength();i++)<br />
  {	<br />
    buffer[0] = strBytes[i];<br />
    digit = strtol( buffer, 0, 16 ); //you could also use sscanf <br />
    TRACE("Digit %i is %d in decimal, %x in hex\n",i,digit,digit);<br />
  }<br />

How to handle the ChildFrames ?

Tomasz Sowinski22-Jun-01 7:18

Tomasz Sowinski

22-Jun-01 7:18

Shouldn't it be
buffer[1] = 0; // //null terminator required

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

Dooh!

Jim Howard22-Jun-01 8:12

Jim Howard

22-Jun-01 8:12

Of it should it should. I knew that, I just wanted to make sure that you knew it also!

Jim Dead | X|

Radovan L.22-Jun-01 5:49

Radovan L.

22-Jun-01 5:49

Fist iam a newbie with MFC!

But i was asked to make an program that reads from the Comport, that is connected whit a windmachine.The windmachine sends me diffrent sort of kordinates(16 diffrent cords).
My problem here is that the user wants to choose how many kords he wants to display,my idea was to create a new ChildFrame for each kord that is selected to show.And store the ChildFrames in a array and if there comes new kords from the Comport use the ChildeFrame array to send right kords to the right ChildFrame.
The ChildFrame has a ChildView(CWnd derived) wich recives the kords for painting(OnPaint()).
I used the appwizzard (MDI,No doc/view)

I wounder if i am on the right track?
If u have a better soulotion for doing this a better way post a message here !
(Sorry my bad english)

Memory Leak

Nitish Kumar22-Jun-01 5:42

Nitish Kumar

22-Jun-01 5:42

when ever i run a program in debug mode, after i exit the program, i always get a message "Detected Memory Leak".. what do i do about it??? can you tell me where i am missing or making an error??

Nitish

Re: Memory Leak

Malcolm McMahon22-Jun-01 6:03

22-Jun-01 6:03

It's telling you you created heap objects and never deleted them. For every new that's executed there needs to be a delete.

You may need to add destructors to some of your classes to delete anything the class allocates.

Think about the lifetime of everything you create with new. Are you overwriting the only pointer to an object (orphaning it)?

Re: Memory Leak

Tim Deveaux22-Jun-01 6:42

Tim Deveaux

22-Jun-01 6:42

Have a look at "HOWTO: Use _crtBreakAlloc to Debug a Memory Allocation"
Article ID: Q151585 in the MSDN.

remember

Amit Jain22-Jun-01 7:51

Amit Jain

22-Jun-01 7:51

if you make a variable with new, use delete.
if you make an array of variables with new, use delete[].

--
Peace,
Amit Jain

Re: remember

Malcolm McMahon25-Jun-01 4:48

25-Jun-01 4:48

Does VC++ distinguish between delete and delete[] then? With most compilers the [] is no more than a comment.

Re: remember

Amit Jain25-Jun-01 5:30

Amit Jain

25-Jun-01 5:30

Hm, I wonder if that's a bug with VC++ or the other compilers? But yes, VC++ DEFINITELY distinguishes between the two... You should too, just in case.

--
Peace,
Amit Jain

Re: remember

Malcolm McMahon25-Jun-01 6:09

25-Jun-01 6:09

In order to properly delete an array (call the destructors of each element) the delete routine must work out the size of the array from hidden runtime information, probably the allocation size is stored immediately before the pointer. It would follow that there's very little point in using a separate delete implementation for arrays and single object allocations (a single object allocation being indistinguishable from an array of length 1).

yupyup

Amit Jain25-Jun-01 7:23

Amit Jain

25-Jun-01 7:23

I'm sure that's true and all, but regardless, if you're doing it in VC++, you're using delete[] for a dynamically allocated array, and delete for a single item.

--
Peace,
Amit Jain

Re: yupyup

Malcolm McMahon26-Jun-01 3:23

26-Jun-01 3:23

Yes you should (for clarity at least).

I'd be surprised, though, if it makes any difference to the code generated.

Re: yupyup

Tomasz Sowinski26-Jun-01 3:36

Tomasz Sowinski

26-Jun-01 3:36

> I'd be surprised, though, if it makes any difference to
> the code generated.

It makes a substantial difference. If you use new to allocate an array of objects and delete without square brackets, the destructors will not be called except one for element at 0th index.

CMyClass *p = new CMyClass[10];
// ... use p
delete p; // error -> only one d'tor call

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

Re: yupyup

Malcolm McMahon26-Jun-01 5:05

26-Jun-01 5:05

You're right. Surprised I am . It even comes up with an error message.
Blush | :O

VC++ COM and ASP stuff

lea22-Jun-01 4:58

22-Jun-01 4:58

Hello,

I know very little about C++ and what I do know has been classes compiled on Borlands free command line compiler. I have a task to complete with VC++, and after opening it up got scared looking at all those buttons and menus. Nether the less, a job is a job.

I need to create a COM dll file that I can access via ASP or VB. I've searched the web for this stuff and can't find much at all.

I found the ATL COM app wizard and setup a basic DLL outline, then added a new ATL object. I added a method to that and at this stage can compile the lot and view the dll from VB.

My problem (at this stage) seems to be returning any value from the component. VB seems to recorgnise it as a Sub as opposed to a Function. Also, if I try to give the method any other return value appart from HRESULT I get into trouble.

So how do I make a call like "a = b.Add(4, 6)" in VB to get the result retruned into a?

I can see my next problem coming, how do I return an array??

Thanks anyone Suspicious | :suss:

Lea

Carlos Antollini22-Jun-01 5:26

Carlos Antollini

22-Jun-01 5:26

In the IDL you must define:
[out, retval] BSTR* strVal
[out, retval] int* nVal
etc;

Carlos Antollini.

lea22-Jun-01 5:42

22-Jun-01 5:42

OK, like I said I don't have a clue. So you mean like this?

[id(1), helpstring("method Add")] HRESULT Add([out, retval] BSTR* strVal);

And then what about the function in the class, how do I assign my newly created and calculated value to it? like this?

strVal = myNewNumber;

and the class itself, do I add in the same as above? like this??

STDMETHODIMP Ccalc::Add([out, retval] BSTR* strVal) { ..

Thanks Confused | :confused:

Lea

Carlos Antollini22-Jun-01 6:22

Carlos Antollini

22-Jun-01 6:22

>[id(1), helpstring("method Add")] HRESULT Add([out, retval] BSTR* strVal);
Ok. This is if you want to return a value, but if you need from VB something like this:
b = obj.Add(1,2)
Must be:
[id(1), helpstring("method Add")] HRESULT Add([in] int nVal1, [in]int nVal2, [out, retval] BSTR* strVal);

>And then what about the function in the class

STDMETHODIMP Ccalc::Add(int nVal1, int nVal2, BSTR* strVal)
{
CString strBuff = _T("Val to return");
//Do something
::SysFreeString(*strVal);
*strVal = strBuff.AllocSysString();
}

Do you Understand?

Good Luck
Smile | :)

Carlos Antollini.

lea25-Jun-01 4:36

25-Jun-01 4:36

Nearly there. This is a stupid one, but the CString (which I haven't used before) doesn't seem to work.

OK OK, forget that, how do I return an array to VB? Or even a string?

char anArray[2];
cpystr(anArray[0], "hello");
cpystr(anArray[1], ello");

*strVal = anArray;

Anything like this?? Confused | :confused:

Lea

lea25-Jun-01 4:36