Plain C++ Code to Invoke COM Method with parameter

Question

I have been able to create an instance of SharePoint.OpenDocuments.1 ActiveX Control like so:

CLSID clsid;
HRESULT hResult; 
IDispatch *pWApp;
LPCOLESTR strPid = L"SharePoint.OpenDocuments.1";

CoInitialize(NULL);  
hResult = CLSIDFromProgID(strPid, &clsid);
if(SUCCEEDED(hResult))
    hResult = CoCreateInstance(clsid, NULL, CLSCTX_ALL , IID_IDispatch, (void **)&pWApp);

I have some trouble invoking the "EditDocument" method with a document name. I can't figure out how to invoke or use Variants.

Any code tips?

Use the #import directive to avoid having to write late-bound code. That's only easy in a scripting language, definitely not in C++. — Hans Passant
– Hans Passant, Commented Aug 4, 2012 at 17:43

Jerry Coffin · Accepted Answer · 2012-08-03 19:13:16Z

2

At least if I'm reading the docs correctly, you need a BSTR, which you can create with SysAllocString.

answered Aug 3, 2012 at 19:13

Jerry Coffin

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1 Comment

Tamás Szelei Over a year ago

This is very likely the issue. The difference is that SysAllocString will add a prefix length to the string, while the manual way won't (more precisely, the first two bytes will be treated as length). Even better, use the _bstr_t class that manages the string and calls SysFreeString when needed.

yms · Accepted Answer · 2012-08-04 17:06:52Z

0

If you are using ATL in your C++ project, you can easily create a BSTR string by using the class CComBSTR and pass it as parameter to OpenDocuments.EditDocuments

CComBSTR tempBstr = _T("c:\\myfolder\\myfile.txt");
someObj->SomeMethodThatUsesBSTR(tempBstr);

If you are not using ATL, you can then use the class bstr_t from comutil.h the same way:

bstr_t tempBstr = _T("c:\\myfolder\\myfile.txt");
someObj->SomeMethodThatUsesBSTR(tempBstr.GetBSTR());

Both classes (CComBSTR and bstr_t) are just wrappers that will call SysAllocString and SysFreeString internally.

edited Aug 4, 2012 at 17:06

answered Aug 3, 2012 at 19:33

yms

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