ATL Problems ??? Ask for help !

[Leesen]

Hi, all In Atl project ,how can I return the user define type? For example , I have define a Struct ,and I want to return the Struct type in a function, and I plan to utilize the return Struct type in VB through the com. What should I do ? I have try some ways ,but failed. Another similar problem. I have two ATL Object in my Atl project , Teacher and Student . And student is a private property of Teacher ,now I want to construct a function in Teacher to return the Student property .How should I do ? Sincerely ask for help. Who can tell me how to do , or give me some similar source code which resovle the above problems . I'll appreciate it . Regards.

[Vi2]

Q2. You can pass the IStudent interface as well as any other data from ITeacher interface. Q1. In IDL-file

typedef [uuid(XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX), helpstring("Help")]
struct _SomeStruct
{
int i;
BSTR str;
...
} SomeStruct;

[...,dual,...]
interface IO : IDispatch
{
[id(1)] HRESULT M1([in] SomeStruct ss);
[id(2)] HRESULT M2([in,out] SomeStruct *ss);
[id(3)] HRESULT M3([out,retval] SomeStruct* *ss);
[id(4)] HRESULT M4([in,out] SAFEARRAY(SomeStruct) * ssbs);
};

With best wishes, Vita

[Leesen]

thank you . Q1 has been resovled following your suggestion. but Q2 remail abcuse. I mean I can not construct the CStudent object in CTeacher. Details as follows. In the construction function of the CTeacher : CTeacher() { IStudent * m_student =new CStudent(); return; } There are some compiler errors. It says that the CStudent cannot instantiate abstract class due to following members:QueryInterface,AddRef,Release. How should I do to resolve the problem. thx. Regards.

[Vi2]

If you are in ATL, you have several ways to do it.

// CTeacher has a member: IStudent * m_student
// or it is better: CComPtr<IStudent> m_student

1. With the class factory of CStudent.
   if( FAILED(CStudent::_CreatorClass::CreateInstance(NULL,IID_IStudent, (void**)&m_student)) )
   return E_FAIL;

2. With the static method of the generic ATL CComObject.
   CComObject<CStudent>* pCStudent;
   if( FAILED(pCStudent->CreateInstance(&pCStudent)) || FAILED(pCStudent->QueryInterface(&m_student)) )
   return E_FAIL;

3. With the original COM method.
   if( FAILED(CoCreateInstance(CLSID_Student,NULL,CLSCTX_ALL,IID_IStudent, (void**)&m_student)) )
   return E_FAIL;

With best wishes, Vita

[Leesen]

Hi, all Some problems about ATL Com: 1.I have create two ATL Object: CStudent and CTeacher . The simple source code listed as follow: (some code auto generated by ATL have been skiped) class CStudent { private: long m_age; public: CStudent():m_age(10) { } //...other code auto generated by ATL }; class CTeacher { private: IStudent* m_aStudent; public: CTeacher() { //create an instance of the com CoCreateInstance(CLSID_Student,NULL,CLSCTX_ALL,IID_IStudent, (void**)&m_aStudent); } //...other code auto generated by ATL } 2.Then I add a "IStudent * OneStudent" property for ITeacher ,to access the m_aStudent. The implemention of the property are listed as below: STDMETHODIMP CTeacher::get_OneStudent(IStudent *pVal) { AFX_MANAGE_STATE(AfxGetStaticModuleState()) // TODO: Add your implementation code here *pVal = * m_aStudent; return S_OK; } STDMETHODIMP CTeacher::put_OneStudent(IStudent *newVal) { AFX_MANAGE_STATE(AfxGetStaticModuleState()) // TODO: Add your implementation code here *m_aStudent = *newVal ; return S_OK; } 3.Now I type some VB code to test the com ,but some compiler errors occurrs. VB Code: Dim s As Student Dim t As New Teacher s = t.OneStudent the last sentence "s = t.OneStudent" have compiler errors. Errors:function or interface marked as restricted ,or the function use an Automation type not supported in Visual Basic I guess the errors caused by the type dismatch between IStudnet and CStudent.But I did not know how to resolve it . So who can tell me how to return the m_aStudent that can be supproted in vb?? thx. Regards.

[Philippe Mori]

I think that you should implement get_OneStudent that way (and the IDL updated appropriatly):

STDMETHODIMP CTeacher::get_OneStudent(IStudent **pVal)
{
AFX_MANAGE_STATE(AfxGetStaticModuleState())

// TODO: Add your implementation code here
*pVal = m_aStudent;
if (*pVal) {
(*pVal)->AddRef();
}
return S_OK;
}

You cannot copy the interface (nothing will be copied since the interface has no data in itself) and output parameter must be a [out]pointer to what you want to returns (you want to returns a IStudent * so you must use IStudent **). Philippe Mori