Question

I have a browser helper object written in C++ but I have a problem when recieving a OnHelp HtmlEvent.

When I try to access a attribute the browser crashes.

VARIANT_BOOL STDMETHODCALLTYPE OnHelp(IHTMLEventObj2 *pEvtObj)
{
    std::cout << "OnHelp Event" << std::endl;

    if(pEvtObj != NULL) {
        VARIANT var;
        pEvtObj->getAttribute(L"formID", 0, &var);
        std::cout << (char*)var.bstrVal << std::endl;
    } 
    else {
        std::cout << "PELEM = NULL" << std::endl;
    }

    return VARIANT_TRUE;
}

It crashes on the getAttribute line for some reason? When doing this in C# it works perfectly. I hope somebody can help me fix this.

Edit:

The real problem was with the parameter I needed to use IHTMLEventObj and then query for IHTMLEventObj2.

VARIANT_BOOL STDMETHODCALLTYPE OnHelp(IHTMLEventObj *pEvtObj)
{
    IHTMLEventObj2 *pEvtObj2;
    pEvtObj->QueryInterface(IID_IHTMLEventObj2, (void**)&pEvtObj2);

    if(pEvtObj2 != NULL) {
        VARIANT var;
        pEvtObj2->getAttribute(CComBSTR(L"url"), 0, &var);
        std::cout << _bstr_t(var.bstrVal) << std::endl;
    } 
    else {
        std::cout << "PELEM = NULL" << std::endl;
    }

    return VARIANT_TRUE;
}

Answer 1

The first arg for getAttribute is a BSTR, but your passing a wchar_t*/unsigned int * depending on VC compile settings.
BSTR is a system string which is expected to be deallocated by the receiving method.

Try

#define DOM_ANON_STRING(x)          (_bstr_t(x))
pEvtObj->getAttribute(DOM_ANON_STRING(L"formID"), 0, &var);