How to use CoCreateInstance() to get a com object?

c++ com mingw

34,943

Solution 1

Your COM class implements some interfaces and each interface has its IID identifier. So you need to get it from your COM component implementation. It's your code and you are expected to provide the identifier which exactly specifies what interface you are requesting.

Some COM classes implement well known interface, esp. IDispatch, the identifier for which is IID_IDispatch, or __uuidof(IDispatch).

UPD. Since you found that the interface of interest is Isesoft, your code will be:

CLSID clsid;
RIID iid;
IDispatch* pDispatch;
HRESULT nResult1 = CLSIDFromProgID(OLESTR("se.mysoft"), &clsid);
HRESULT nResult2 = CoCreateInstance(clsid, NULL, CLSCTX_INPROC_SERVER,
  IID_Isesoft, (void **) &pDispatch);

To get Isesoft and IID_Isesoft, __uuidof(Isesoft) available to C++ code, you will need to import the definitions, which is typically either of then two:

additional vendor SDK includes e.g. #include "isesoft\sdk.h"
or #import "libid:..." with type library identifier (namespace and other attributes apply)

When you have HRESULT codes indicating failures, make sure to post the values.

Solution 2

I suppose that your CLSID is correct, since hr has a value of 0. From the extract of your idl.file, I conclude that the interface‘s ID is {F3F54BC2-D6D1-4A85-B943-16287ECEA64C} and its name Isesoft. Your present code provides a pointer to IDispatch and hr1 should be 0 if hr is 0. To get a raw COM pointer to this interface you must pass the CLSID and the IID as well as the address of a pointer to Isesoft.

Now change your code:

CLSID clsid;
RIID iid;
IseSoft* pIceSoft; 
HRESULT hr = CLSIDFromProgID(OLESTR("se.mysoft"),&clsid);
HRESULT hr2 = IIDFromString(OLESTR("{F3F54BC2-D6D1-4A85-B943-16287ECEA64C}"), &iid);
HRESULT hr3 = CoCreateInstance(clsid, NULL, CLSCTX_INPROC_SERVER, iid, (void **)&pIseSoft);

A final remark: Since your hr1 returns a fail which it shouldn't, I presume that something is wrong with the CLSID. You can find the correct CLSID in the idl file from where you got the IID oft he interface.

Nevertheless, with your code all you would get is a useless IDispatch pointer, because that is what you are asking for.

Solution 3

You should know the interface you want on your object, let call it IMyInterface.

IMyInterface* pItf = NULL;
hr = CoCreateInstance(clsid, NULL, CLSCTX_INPROC_SERVER, IID_IMyInterface, (void**)&pItf);

34,943

Author by

CodeCat

Updated on September 21, 2021

Comments

CodeCat almost 3 years

I had registered a COM component.And I want to call it.

CLSID clsid;
RIID iid;
HRESULT hr = CLSIDFromProgID(OLESTR("se.mysoft"),&clsid);
LPVOID *pRet;
HRESULT hr1 = CoCreateInstance(clsid, NULL, CLSCTX_INPROC_SERVER, iid, pRet);

I can get the clsid successful, but where can I get the iid ?

I used OLE VIEWER find interface:

 [
 odl,
 uuid(F3F54BC2-D6D1-4A85-B943-16287ECEA64C),
 helpstring("Isesoft Interface"),
 dual,
 oleautomation
 ]
 interface Isesoft : IDispatch {

Then I changed my code:

CLSID clsid;
RIID iid;
IDispatch* pDispatch;
HRESULT hr = CLSIDFromProgID(OLESTR("se.mysoft"),&clsid);
HRESULT hr1 = CoCreateInstance(clsid, NULL, CLSCTX_INPROC_SERVER,  IID_IDispatch,(void **)&pDispatch);

But hr1 returned failed.

CodeCat almost 11 years

The com class isn't created by me and I can't see the code and IID identifier.Then I use IID_IDispatch ,but the program can't work(It can be compiled but failed in running).
Roman R. almost 11 years

If the COM library/component is not yours, you need additional information from the vendor, or you might possibly looks up the identifiers via type library (see COM/OLE Viewer tool).
CodeCat almost 11 years

Where can i find the interface? I don't have the COM component's source code. I can call it in VB: set se = createobject("se.mysoft") I don't know how to call it in c++.
CodeCat almost 11 years

I can call it in VB: set se = createobject("se.mysoft"). I don't know how to call it in c++
sehe almost 11 years

"Some COM classes implement well known interface" Well then, might be worth pointing out that all COM classes implement at least IUnknown :)
CodeCat almost 11 years

I found the implement, but I still failed.
AndersK almost 11 years

@CodeCat have you tried importing the .dll ? That generates header files that you can include to access the COM object. Just write #import "yourdll.dll" in your cpp file (and make sure you got a path to it)
CodeCat almost 11 years

when I imported dll file and compiled it , the compiler show many error.
CodeCat almost 11 years

I found a header file of the COM component. I am trying to include and compile it. But here are so many errors. I am repairing it.
CodeCat almost 11 years

My compiler is MINGW, I can't use '__uuidof'.
Roman R. almost 11 years

IID_Isesoft is another option - depends on the header you use, it might/should be defined there this way.
CodeCat almost 11 years

IID_Isesoft was not declared. The header I use only include one class Idmsoft.
Alberto Oliveira almost 3 years

It works!!!!! Thanks, Very Mutch