Re: Problem while destroying SafeArray - COM Discussion Boards

Re: opening an Excel file

2-Mar-04 6:24

If you don't know what they are, then chances are they are optional parameters.
You can handle this by passing a variant that has a particular makeup,
namely

v.vt = VT_ERROR;
v.scode = DISP_E_PARAMNOTFOUND;

and using the variant for any 'optional' arguments.

Steve S

Liate2-Mar-04 19:55

Liate

2-Mar-04 19:55

This is exatly what I was looking for!
problem is solved.
thanks.

Problem while destroying SafeArray

mandarpb1-Mar-04 22:09

mandarpb

1-Mar-04 22:09

Currently I am developing an application, which uses SafeArray to pass UDT. When I create SafeArray at server side and destoy it at client side, there is no issue. But when I create SafeArray at client side, and tries to destoy it at server side, the method returns with HRESULT values (error 0x800703E6)-"Invalid access to memory location" .

The procedure at both ends as below -
SafeArray consists of array of SafeArrays. So first create & access root SafeArray, fill it. Then access SafeArray at level 2, fill it, unaccess it , unaccess root level SafeArray, destroy root level SafeArray.

It works in client side, ut fails at server side.

Steve S1-Mar-04 22:22

1-Mar-04 22:22

What arguments are you passing to the SafeArrayCreate function to create the outer and inner ones

Steve S

Anonymous2-Mar-04 19:35

2-Mar-04 19:35

1. The client code for creation is - SafeArrayCreate( VT_VARIANT, 1, &saBounds) where saBounds[] = (0, 20}, It consists of other SafeArrays and normal data types like INT, BSTR.
2. Passed to server as - SetData(SAFEARRAY **psaData)
3. At server side - hr = SafeArrayDestroy( *psaProjConfig )
4. The hr is S_OK at step 3.
5. But when method returns, client throws error as "Invalid access to memory location"

Thanks for the interest shown.

Regards,
Mandar

Steve S2-Mar-04 23:21

2-Mar-04 23:21

1-4 No problem, that's exactly right.
5. Is the parameter [in,out] by any chance?
If so, that's your problem. You need to do
4. hr = SafeArrayDestroy(*psaProjConfig);
*psaProjConfig = NULL;
That tells OLEAUT32 (which contains the automation marshalling code) that there is nothing to marshall back. Without that step, the marshaller at the client end will be trying to marshall freed memory.

Hope that helps

Steve S

Anonymous5-Mar-04 3:04

5-Mar-04 3:04

Thanks Steve. Prevoiusly SafeArray was [in] parameter. As pointed out by you, I make it [in,out] parameter as we are changing its value. But till I am getting error after returning the method.

Steve S7-Mar-04 21:56

7-Mar-04 21:56

But are you really changing the value?
In my example, after destroying the SafeArray on the server side, I set the value to be NULL. Since it's an in/out, you pass not 'SAFEARRAY*' but 'SAFEARRAY**', of course.

I know 'Mr.Prakash' says it's not safe to destroy the array on the server side, but that isn't true.

I think it's still failing because the automation marshaller is trying to send back the deleted safearray.

Steve S

Anonymous10-Mar-04 2:06

10-Mar-04 2:06

Hi,

I solved the problem. I write the code to destoying the SafeArray at Client side only, after returnung method from Server. My method has SafeArray as a [in] parameter. Now it is working properly.

Thank for the help.

Prakash Nadar6-Mar-04 6:45

Prakash Nadar

6-Mar-04 6:45

mandarpb wrote:
But when I create SafeArray at client side, and tries to destoy it at server side

I guess it should not be done, pointers should be destroyed by the owner of the pointer i.e client in this case.

This space is empty.

Anonymous10-Mar-04 2:07

10-Mar-04 2:07

Hi,

Yes, your solution is right.

Thank for the help.

Regards,
Mandar

variant arrays..

safee ullah29-Feb-04 21:08

safee ullah

29-Feb-04 21:08

any place to get detailed info on variant arrays..and how to use them??

Re: variant arrays..

Steve S1-Mar-04 0:12

1-Mar-04 0:12

MSDN.
A variant array is just that, an array of VARIANT types, use just like any other kind of SAFEARRAY, except of course, that your basic array type is VARIANT rather than BSTR or whatever.

It's worth remembering that SafeArrayGetElement and SafeArrayPutElement deal with COPYING the data they work with, so Get gives you a new, second, copy and Put will not care what you do with the original you pass it. This is true for other "managed" types (IUnknown, BSTR etc) not just VARIANTs.

Of course, your element type is determined by the .vt member of each element, not by the type of the array, but each element is the same size Smile | :)

Steve S

variant types..

anand12312329-Feb-04 20:06

anand123123

29-Feb-04 20:06

guys i have a variant..being returned by a method..how do i get its vt..and also how do i then extract the value from this variant..

thanks

-anand

ian mariano29-Feb-04 20:45

ian mariano

29-Feb-04 20:45

If v is the variable the VARIANT is returned in, then v.vt is the type (VARTYPE)

VARIANT and VARIANTARG

Ian Mariano - http://www.ian-space.com/

"We are all wave equations in the information matrix of the universe" - me

safee ullah29-Feb-04 21:03

safee ullah

29-Feb-04 21:03

hey thanks ian..

one more thing plz..how do i then get the value from this variant?

thanks

Steve S1-Mar-04 0:16

1-Mar-04 0:16

Depends what it is. There are various macros beginning V_ that you might find useful.

Say you have

VARIANT v;
HRESULT x = myobj.mycall(...,...,..., &v);

You can have code like this:

switch(V_VT(&v))
{
case VT_BSTR: // Returned a string
// V_BSTR(&v) is the BSTR being passed back...
break;
case VT_I4: // Returned a 'long'
// V_I4(&v) is the number

and so on.

Does that help?

Steve S

ian mariano1-Mar-04 11:39

ian mariano

1-Mar-04 11:39

Dang! You beat me to it Wink | ;)

Ian Mariano - http://www.ian-space.com/

"We are all wave equations in the information matrix of the universe" - me