Re: VB function called from c++

From:

"Jake" <jakethedog317@yahoo.com>

Newsgroups:

microsoft.public.vc.language

Date:

21 Nov 2006 11:25:21 -0800

Message-ID:

<1164137121.599386.157590@b28g2000cwb.googlegroups.com>

Alex Blekhman wrote:

"Jake" wrote:

This is my code

int u_dll_imstest_call(wchar_t *TheConnectString, wchar_t
*TheTable,
wchar_t *TheFields, wchar_t *ThePopupTitle, wchar_t
*TheOrderBy,
wchar_t *TheWhereClause, wchar_t *ThePosition)
{
// Declare an HRESULT and a pointer to the clsCat16
interface
HRESULT hr;

_bstr_t bTheConnectString(TheConnectString);
//TheConnectString
creates a _bstr_t wrapper
_bstr_t bTheTable(TheTable); //TheTable creates a _bstr_t
wrapper
_bstr_t bTheFields(TheFields); //TheFields creates a
_bstr_t wrapper
_bstr_t bThePopupTitle(ThePopupTitle); // ThePopupTitle
creates a
_bstr_t wrapper
_bstr_t bTheOrderBy(TheOrderBy); //TheOrderBy creates a
_bstr_t
wrapper
_bstr_t bTheWhereClause(TheWhereClause); //TheWhereClause
creates a
_bstr_t wrapper
_bstr_t bThePosition(ThePosition); //ThePosition creates a
_bstr_t
wrapper
_bstr_t bvalue;

_clsCat16Ptr ptrCat16(__uuidof(_clsCat16));

// Now we will intilize COM
hr = CoInitialize(0);

First of all, call CoInitialize _before_ you try to create
object's instance. CoInitialize should be called before any
COM related operations.

if(SUCCEEDED(hr))
{
bvalue = _clsCat16Ptr->Popup(bTheConnectString, bTheTable,
bTheFields, bThePopupTitle, bTheOrderBy, bTheWhereClause,
bThePosition,
bvalue);

  ^^^^^^

Last parameter is redundant. Popup method will return
_bstr_t as return value. Also, according to .TLH file Popup
method expects BSTR* parameters. So, you should call
_bstr_t::GetAddress method as I pointed in previous post:

bvalue = _clsCat16Ptr->Popup(
    bTheConnectString.GetAddress(),
    bTheTable.GetAddress(),
    bTheFields.GetAddress(),
    ....);

Also, it's considered bad C++ style to declare variables far
from the place where they are used. It's much more elegant
and readable to declare variables when they first used, but
not earlier. For example, instead of declaring HRESULT hr in
the beginning of the function declare it where you call to
CoInitialize:

HRESULT hr = CoInitialize(0);

The same can be said about _bstr_t bvalue variable.

HTH
Alex

Alex that did help with the compile but for some reason the getaddress
is returning nulls for each of the calls.

As you can see from the code I set it up using the smart pointer and I
also tried it using the createinstance which is currently commented
out. I both instances I can see the values for the wchar_t* that are
passed to the function and I can see the values in the _bstr_ instances
as well. If I follow the debugger through the GetAddress for each call
I am seeing Nulls returned Since these values are Null it is crashing
in the VB call

This is the VB call that I see in my tli file

inline _bstr_t _clsCat16::Popup ( BSTR * TheConnectString, BSTR *
TheTable, BSTR * TheFields, BSTR * ThePopupTitle, BSTR * TheOrderBy,
BSTR * TheWhereClause, BSTR * ThePosition ) {
    BSTR _result = 0;
    HRESULT _hr = raw_Popup(TheConnectString, TheTable, TheFields,
ThePopupTitle, TheOrderBy, TheWhereClause, ThePosition, &_result);
    if (FAILED(_hr)) _com_issue_errorex(_hr, this, __uuidof(this));
<----Crashes here
    return _bstr_t(_result, false);
}

any idea as to what stupid mistake I might be making?

BTW here is the latest code and what is being passed

/Values being passed//

//TheConnectString = L"Provider = Microsoft.Jet.OLEDB.4.0;Data
Source=C:\\Imstestfor8.2\\database\\CAT16.mdb";
//TheTable = L"USR";
//TheFields = L"USERNAME,Name,USER_ID,ID,U_LOGIN,Log-in";
//ThePopupTitle = L"User Table";
//TheOrderBy = L"USERNAME";
//TheWhereClause = NULL;
//ThePosition = NULL;

int u_imstest_call(wchar_t *TheConnectString, wchar_t *TheTable,
wchar_t *TheFields, wchar_t *ThePopupTitle, wchar_t *TheOrderBy,
wchar_t *TheWhereClause, wchar_t *ThePosition)
{
    // Now we will intilize COM
    HRESULT hr = CoInitialize(0);

    if(SUCCEEDED(hr))
    {
        _clsCat16Ptr ptrCat16(__uuidof(clsCat16)); //Smart pointer wrapper

        //_clsCat16 *IclsCat16 = NULL;
        //hr = CoCreateInstance(__uuidof (clsCat16),
        // NULL,
        // CLSCTX_INPROC_SERVER,
          // _uuidof (_clsCat16),
            // (void**) &IclsCat16);

    // if(SUCCEEDED(hr))
    // {
            _bstr_t bTheConnectString(TheConnectString); //TheConnectString
creates a _bstr_t wrapper
            _bstr_t bTheTable(TheTable); //TheTable creates a _bstr_t wrapper
            _bstr_t bTheFields(TheFields); //TheFields creates a _bstr_t wrapper
            _bstr_t bThePopupTitle(ThePopupTitle); // ThePopupTitle creates a
_bstr_t wrapper
            _bstr_t bTheOrderBy(TheOrderBy); //TheOrderBy creates a _bstr_t
wrapper
            _bstr_t bTheWhereClause(TheWhereClause); //TheWhereClause creates a
_bstr_t wrapper
            _bstr_t bThePosition(ThePosition); //ThePosition creates a _bstr_t
wrapper

            _bstr_t bvalue = ptrCat16->Popup(bTheConnectString.GetAddress(),
bTheTable.GetAddress(),
                                             bTheFields.GetAddress(),
bThePopupTitle.GetAddress(),
                                             bTheOrderBy.GetAddress(), bTheWhereClause.GetAddress(),
                                             bThePosition.GetAddress());
            CoUninitialize();
            return 0;
        //}
    // else
    // {
    // return 1;
    // }
    }
    else
    {
        return 1;
    }
}

Thanks again for your help
Jake