QueryInterface 实现及使用的完整的例子

大家好，又见面了，我是你们的朋友全栈君。

下面我们将把前面所提到过和各代码段组合起来，以构成一个说明QueryInterface 实现及使用的完整例子。
总的来说可以将这些代码分成三部分。
第一部分是接口IX、 IY 和 IZ 的定义部分。接口 IUnknown 的定义在 Win32 SDK 的头文件 1 见UNKNWN . H 中。
第二部分是组件的实现。类 CA 实现了一个支持 IX 和 IY 接口的组件。QueryInterface的实现同前一节中给出的实现是一样的。在类CA的末尾给出了CreateInstance 的定义。客户可以使用此函数来创建类 CA 所代表的组件并返回一个指向其 IUnknown 接口的指针。
在定义好 CreateInstance函数之后，下面定义的是各接口的 IID 结构。从这些定义可以看出 IID 结构是一个相当大的结构。

清单中的第三部分也就是最后一部分是main 函数，它表示示例程序中的客户。

#include
<
iostream
>

#include
<
objbase.h
>

#include
<
windows.h
>

using

namespace
std;

void
trace(
const

char

*
msg){cout
<<
msg
<<
endl;}

//
interfaces

interface
IX:IUnknown
{

virtual

void
_stdcall Fx()
=
0
;
};

interface
IY:IUnknown
{

virtual

void
_stdcall Fy()
=
0
;
};

interface
IZ:IUnknown
{

virtual

void
_stdcall Fz()
=
0
;
};

//
forward references for guids

extern

const
IID IID_IX;

extern

const
IID IID_IY;

extern

const
IID IID_IZ;

//
component

class
CA:
public
IX,
public
IY
{


//
IUnknown implementation


virtual
HRESULT _stdcall QueryInterface(
const
IID
&
iid,
void

**
ppv);

virtual
ULONG _stdcall AddRef(){

return

0
;}

virtual
ULONG _stdcall Release(){

return

0
;}

//
interface IX implementation


virtual

void
_stdcall Fx() {cout
<<
“
FX
“
<<
endl;MessageBox(NULL,
“
hello world
“
,
“
caption
“
,MB_OK);};

//
interface IY implementation


virtual

void
_stdcall Fy(){cout
<<
“
FY
“
<<
endl;}

};

HRESULT _stdcall CA::QueryInterface(
const
IID
&
iid,
void

**
ppv)
{


if
(iid
==
IID_IUnknown)
    {

        trace(
“
QueryInterface:return pointer to IUnknown
“
);

*
ppv
=
static_cast
<
IX
*>
(
this
);
    }

else

if
(iid
==
IID_IX)
    {

        trace(
“
QueryInterface:Return pointer to IX.
“
);

*
ppv
=
static_cast
<
IX
*>
(
this
);
    }

else

if
(iid
==
IID_IY)
    {

        trace(
“
QuertyInterface:Return pointer to IY
“
);

*
ppv
=
static_cast
<
IY
*>
(
this
);
    }

else

    {

        trace(
“
QuertyInterface:Interface not supported
“
);

*
ppv
=
NULL;

return
E_NOINTERFACE;
    }
    reinterpret_cast
<
IUnknown
*>
(
*
ppv)
->
AddRef();

return
S_OK;

}

//
creation function

IUnknown
*
CreateInstance()
{

    IUnknown
*
pI
=
static_cast
<
IX
*>
(
new
CA);
    pI
->
AddRef();

return
pI;
}

//
IIDS

//
{C225EDDE-ACFE-4349-AD2B-C7068731F8B3}

static

const
IID IID_IX
=

{
0xc225edde
,
0xacfe
,
0x4349
, {
0xad
,
0x2b
,
0xc7
,
0x6
,
0x87
,
0x31
,
0xf8
,
0xb3
} };

//
{6E3A34D9-1E23-433b-A393-1A4A6A965C80}

static

const
IID IID_IY
=

{
0x6e3a34d9
,
0x1e23
,
0x433b
, {
0xa3
,
0x93
,
0x1a
,
0x4a
,
0x6a
,
0x96
,
0x5c
,
0x80
} };

//
{D8CDFA09-D552-41b9-AA44-8A70D8554A5C}

static

const
IID IID_IZ
=

{
0xd8cdfa09
,
0xd552
,
0x41b9
, {
0xaa
,
0x44
,
0x8a
,
0x70
,
0xd8
,
0x55
,
0x4a
,
0x5c
} };

//
client

int
main()
{

HRESULT hr;
trace(
“
client: Get an IUnknown pointer
“
);

IUnknown
*
pIUnKnown
=
CreateInstance();
trace(
“
client: Get interface IX
“
);

    IX
*
pIX
=
NULL;
    hr
=
pIUnKnown
->
QueryInterface(IID_IX,(
void

**
)
&
pIX);

if
(SUCCEEDED(hr))
    {

        trace(
“
client:Succeeded getting IX
“
);
        pIX
->
Fx();
//
use interface IX

    }
    trace(
“
client: Get interface IY
“
);

IY
*
pIY
=
NULL;
hr
=
pIUnKnown
->
QueryInterface(IID_IY,(
void

**
)
&
pIY);

if
(SUCCEEDED(hr))
    {

        trace(
“
client: Succeeded get IY
“
);
        pIY
->
Fy();
//
use interface IY

    }

trace(
“
client:ask for an unsupporte interface
“
);

IZ
*
pIZ
=
NULL;

    hr
=
pIUnKnown
->
QueryInterface(IID_IZ,(
void

**
)
&
pIZ);

if
(SUCCEEDED(hr))
    {

        trace(
“
client:succeeded in geting interface iz
“
);
        pIZ
->
Fz();
    }

else

    {

        trace(
“
client: could not get interface IZ
“
);
    }
    trace(
“
client: get interface IY from interface IX
“
);

IY
*
pIYfromIX
=
NULL;
hr
=
pIX
->
QueryInterface(IID_IY,(
void

**
)
&
pIYfromIX);

if
(SUCCEEDED(hr))
    {

        trace(
“
client:succeeded getting IY
“
);
        pIYfromIX
->
Fy();
    }
    trace(
“
client: get interface IUNkown from IY
“
);

IUnknown
*
pIUnknownFromIY
=
NULL;
hr
=
pIY
->
QueryInterface(IID_IUnknown,(
void

**
)
&
pIUnknownFromIY);

if
(SUCCEEDED(hr))
    {

        cout
<<
“
Are the IUnknown pointers equal
“
;

if
(pIUnknownFromIY
==
pIUnKnown)
        {

            cout
<<
“
Yes,pIUnknownFromIY==pIUnknown
“
<<
endl;
        }

else

        {

            cout
<<
“
No,pIUnknownFrom IY!=pIUnknown
“
<<
endl;
        }
    }

//
Delete the component

    delete pIUnKnown;