__interface
Microsoft Specific
A Visual C++ interface can be defined as follows:
Can inherit from zero or more base interfaces.
Cannot inherit from a base class.
Can only contain public, pure virtual methods.
Cannot contain constructors, destructors, or operators.
Cannot contain static methods.
Cannot contain data members; properties are allowed.
modifier __interface interface-name {interface-definition};
Remarks
A C++ class or struct could be implemented with these rules, but __interface enforces them.
For example, the following is a sample interface definition:
__interface IMyInterface {
HRESULT CommitX();
HRESULT get_X(BSTR* pbstrName);
};
For information on managed interfaces, see interface class.
Notice that you do not have to explicitly indicate that the CommitX and get_X functions are pure virtual. An equivalent declaration for the first function would be:
virtual HRESULT CommitX() = 0;
__interface implies the novtable __declspec modifier.
Example
The following sample shows how to use properties declared in an interface.
// deriv_interface.cpp
#define _ATL_ATTRIBUTES 1
#include <atlbase.h>
#include <atlcom.h>
#include <string.h>
#include <comdef.h>
#include <stdio.h>
[module(name="test")];
[ object, uuid("00000000-0000-0000-0000-000000000001"), library_block ]
__interface IFace {
[ id(0) ] int int_data;
[ id(5) ] BSTR bstr_data;
};
[ coclass, uuid("00000000-0000-0000-0000-000000000002") ]
class MyClass : public IFace {
private:
int m_i;
BSTR m_bstr;
public:
MyClass()
{
m_i = 0;
m_bstr = 0;
}
~MyClass()
{
if (m_bstr)
::SysFreeString(m_bstr);
}
int get_int_data()
{
return m_i;
}
void put_int_data(int _i)
{
m_i = _i;
}
BSTR get_bstr_data()
{
BSTR bstr = ::SysAllocString(m_bstr);
return bstr;
}
void put_bstr_data(BSTR bstr)
{
if (m_bstr)
::SysFreeString(m_bstr);
m_bstr = ::SysAllocString(bstr);
}
};
int main()
{
_bstr_t bstr("Testing");
CoInitialize(NULL);
CComObject<MyClass>* p;
CComObject<MyClass>::CreateInstance(&p);
p->int_data = 100;
printf_s("p->int_data = %d\n", p->int_data);
p->bstr_data = bstr;
printf_s("bstr_data = %S\n", p->bstr_data);
}
p->int_data = 100 bstr_data = Testing