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RE: [Mingw-users] Com Pointers - Again..
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From: Lorne E. <le...@bi...> - 2002-11-01 03:32:48
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Hi All,
I am getting mightly sick of looking at this code. :o) I have had a chance
to look at some of the rersources on COM, and COM from c/c++. CComPtr is
still a mystery to me, though I have tried the function call with and
without an initialized COM pointer. Since the error from
"ObjectFromLresult" is the same no matter what, I can only assume that it is
unnecessary. Any assistance, or tips on going forward with this would be
appreciated. I have attached the code in question.. Any assistance would be
greatly appreciated. The code is a simple test class, it's ugly, and I
apologize:
<code>
#ifndef __WIN32_IE_HPP__
#define __WIN32_IE_HPP__
#include <string>
#include <windows.h>
//#include "psdk_files/oleacc.h"
#include "../common/win32_common.hpp"
#include <ole2.h>
#include <mshtml.h>
namespace Win32 {
class IE {
public:
IE(int iMaxBufLen);
~IE();
std::string GetText(HWND hWnd);
private:
int iBufLen;
TCHAR *szBuffer;
CLSID CLSID_HTMLDocument;
HINSTANCE hOLEAcc; //oleacc.dll
typedef HRESULT (STDAPICALLTYPE *LPFNOBJECTFROMLRESULT)(LRESULT lResult,
REFIID riid, WPARAM wParam, void** ppvObject);
LPFNOBJECTFROMLRESULT pfObjectFromLresult; //ObjectFromLresult()
(oleacc.dll)
UINT iMsgHTMLGetObj;
};
};
#endif //__WIN32_IE_HPP__
</code>
</code> <win32_ie.cpp>
#include "win32_ie.hpp"
Win32::IE::IE(int iMaxBufLen) {
//MaxBufLen --Init List
iBufLen = iMaxBufLen;
szBuffer = new TCHAR[iBufLen];
//Init COM
::CoInitialize(NULL);
//Load "Active Accessibility"
if ( (hOLEAcc = ::LoadLibrary("oleacc.dll")) == NULL) {
::MessageBoxPrintf(TEXT("Could not Locate \"Active Accessibility\"
Library"),
TEXT("Active Accessibility is required for this application to
operate correctly."));
return;
}
//Load ObjectFromLresult()
if ( (pfObjectFromLresult = reinterpret_cast<LPFNOBJECTFROMLRESULT>
(::GetProcAddress(hOLEAcc, TEXT("ObjectFromLresult"))) ) == NULL ) {
::MessageBoxPrintf(TEXT("Could not Locate the \"Active Accessibility\"
component"),
TEXT("\"Active Accessibility\" is required for this application to
operate correctly."));
}
if ( (iMsgHTMLGetObj = ::RegisterWindowMessage(
TEXT("WM_HTML_HETOBJECT") )) == 0 ) {
::MessageBoxPrintf(TEXT("Register AA window Message"),
TEXT("\"Active Accessibility\" support could not be loaded."));
}
if (::CLSIDFromProgID(OLESTR("htmlfile"), &CLSID_HTMLDocument) != S_OK) {
::MessageBoxPrintf(TEXT("Failed to get CLSID"), TEXT("Could not get the
CLSID for \"mshtml\".") );
}
}
Win32::IE::~IE() {
delete[] szBuffer;
//Clean Up COM and AA
::FreeLibrary(hOLEAcc);
::CoUninitialize();
}
std::string Win32::IE::GetText(HWND hWnd) {
IHTMLDocument2 *pHTMLDoc = NULL;
LRESULT LRes;
HRESULT hr;
if (::SendMessageTimeout(hWnd, iMsgHTMLGetObj, 0L, 0L, SMTO_ABORTIFHUNG,
1000, reinterpret_cast<DWORD *>(&LRes) ) != 0 ) {
hr = ::CoCreateInstance(CLSID_HTMLDocument, NULL, CLSCTX_ALL,
IID_IHTMLDocument2, reinterpret_cast<LPVOID *>(&pHTMLDoc) );
if (SUCCEEDED(hr)) {
pHTMLDoc->AddRef();
hr = (*pfObjectFromLresult)( LRes, IID_IHTMLDocument2, 0,
reinterpret_cast<LPVOID *>(&pHTMLDoc));
//
if ( SUCCEEDED(hr) ) {
MessageBoxPrintf( TEXT("Cool!"), TEXT("Ready to do stuff!"), hr );
//Do Stuff
pHTMLDoc->Release();
}
else {
switch(hr) {
case E_UNEXPECTED:
::MessageBoxPrintf(TEXT("ObjectFromLresult() failure:"),
TEXT("E_UNEXPECTED") );
break;
case E_NOINTERFACE:
::MessageBoxPrintf(TEXT("ObjectFromLresult() failure:"),
TEXT("E_NOINTERFACE") );
break;
case E_INVALIDARG:
::MessageBoxPrintf(TEXT("ObjectFromLresult() failure:"),
TEXT("E_INVALIDARG") );
break;
default:
::MessageBoxPrintf(TEXT("ObjectFromLresult() failure:"),
TEXT("Unrecognized error!\n%X"), hr );
break;
}
pHTMLDoc->Release();
}
//
}//CoCreateInstance failed
else {
::MessageBoxPrintf( TEXT("Error!"), TEXT("Instance of IHTMLDocument2 coud
not be created.\nError: %d"),
::GetLastError() );
}
}//Message send failed
else {
MessageBoxPrintf( TEXT("Error!"), TEXT("Send Message
(WM_HTML_GETOBJECT) failed.\nError Code: %d"),
::GetLastError() );
}
}
</code>
-----Original Message-----
From: min...@li...
[mailto:min...@li...]On Behalf Of Lorne
Easton
Sent: Wednesday, October 30, 2002 11:36 PM
To: st...@fu...; min...@li...
Subject: RE: [Mingw-users] Com Pointers
Wow! Actually, I'll just send you the source and you can finish the program
for me.. *joke* :o) Thanks for a well informed through and downright helpful
response. Thanks to Luke also. I will have a work through this tomorrow.
Cheers :o)
-----Original Message-----
From: min...@li...
[mailto:min...@li...]On Behalf Of Steve Lee
Sent: Wednesday, October 30, 2002 10:35 PM
To: min...@li...; Lorne Easton
Subject: RE:[Mingw-users] Com Pointers
Lorne Wrote:
> With no ATL, how do you obtain the com void** that the examples here
> use ATL for, using API calls alone? ::CoCreateInstance()? Any
> assistance would be appreciated. If there is some document that
I sould > be reading, please point me in it's direction. All examples
> that I can find seem to use the ATL.
You are not going to like this answer :)
Rather than using ATL to write code that *uses* COM servers, I usually
use the Microsoft extension #import that given a type library (perhaps
in a dll or exe) creates C++ wrapper classes to get at the COM objects
functionality. It uses smartpointers to take care of all the reference
counting and throws exceptions to simplify the error handling. It
also takes care of all the VARIENT packing/unpacking for dispatch
interfaces (IID_IHTMLDocument is a dispatch interface). I doubt that
MinGW supports #import or _com_ptr_t extensions. If not you have
to do it all in raw C/C++ with the APIs as you ask - which is *HARD
WORK*, especially if you are creating a server! On the client side
you still have to take care of reference counting (smartpointers
make life much easier here)! You also need to handle all the possible
errors that come back in the HRESULT returned from all com functions
(there are macros for this).
MFC has its own limited COM support.
However your question seems to be a basic COM question - 'how do
I get at a specific interface?'. The answers is quite simple simple,
given
one interface you use the COM interface function QueryInterface()
(usually known as IUnknown::QueryInterface()) to get any other that
is
supported by the object implementing the interface you have. All
interfaces derive from IUknown and support QueryInterface(). You
obviously need to have a pointer to an interface to start with.
The actual mechanics of how you do that vary depending on what you
are starting with. Assuming You have a pointer to an interface exposed
by an object that also supports one of the IHTMLDocument family,
then all you need to do is call ptr->QueryInterface(IID_IHTMLDocument)
to
get a pointer to it. Perhaps you can create an instance of the object
and get the IID_IHTMLDocument ptr all in one step with CoCreateInterface()
which alows you to specify which interface you want.
As for your specific question you need to don't use CoCreateInstance
because you have already got a pointer to an interface - you use
QueryInterface() BTW did you note that the code needs Active Accessibility
to be installed which I believe may only be true on Windows XP by
default?
The code used 3 ATL features
CComPtr<IHTMLDocument2> - smart pointer, manages AddRef() and Release()
automaticall
CComQIPtr<IHTMLWindow2> - smart point with automatic QueryInterface()
calls
CComVariant - varient support need for paraenters for the dispatch
interface
You need to replace them with the raw API code. I'm not familiar
with the specifics here but it will be very roughly like this (you'll
probably need to
play a bit):
in a .cpp (no c) file
#include "mshtml.h" // have a look in this for fun :)
..
IXMLDocument* pDoc;
..
// CComPtr<IDispatch> spDisp;
IDispatch* pDisp;
// CComQIPtr<IHTMLWindow2> spWin;
IHTMLWindow2* pWin;
// spDoc->get_Script( &spDisp );
HRESULT hr = pDoc->get_Script( &pDisp ); // returns a interface
to a new object
if(FAILED(hr))
// error
// spWin = spDisp;
hr = pDisp->QueryInterface(IID_IHTMLWindow2, &pWin);
if(FAILED(hr))
// error
//spWin->get_document( &spDoc.p ); // reuse of smart pointer I think
pDoc->Release() // I think
hr = pWin->get_document( &pDoc )
if(FAILED(hr))
// error
// spDoc->put_bgColor( CComVariant("red") );
VARIANT v;
::VariantClear(&v);
v.vt = VT_BSTR;
vt.bstrVal = ::SysAllocString(OLESTR("red"));
if (vt.bstrVal == NULL)
// error out of mem
pDoc->put_bgColor( &vt );
::VariantClear(&v); // frees the bstrVal
pDoc->Release();
pDisp->Release();
pWin->Release();
I know which I prefer! I have probably got the referece counting wrong!
There are many resources on COM programming but raw API is not so
common as it is such a lot of work and .NET is making COM even easier.
You could try
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnguion/htm
l/msdn_drguion020298.
asp
as primer or browse from
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/com/comport
al_3qn9.
asp.
Perhaps CodeProject or CodeGurU will help.
Finally, here is an example to parse an XML file using the XML DOM
that I found in the MSDN Lib. I'm not saying it is good, it just
has the basics you need except variants. But hey it must be good
as it uses goto :). Note that the XML DOM is similar in concept to
the HTML DOM which IHTMLDocument is part of.
#define UNICODE
#include <windows.h>
#include <windowsx.h>
#include <stdlib.h>
#include <stdio.h>
#include <io.h>
#include <urlmon.h>
#include <hlink.h>
#include <dispex.h>
#include "mshtml.h"
#include "msxml.h"
#define ASSERT(x) if(!(x)) DebugBreak()
#define CHECK_ERROR(cond, err) if (!(cond)) {pszErr=(err); goto done;}
#define SAFERELEASE(p) if (p) {(p)->Release(); p = NULL;} else ;
int _cdecl main (int argc, char **argv)
{
PSTR pszErr = NULL;
IXMLDocument *pDoc = NULL;
IStream *pStm = NULL;
IPersistStreamInit *pPSI = NULL;
CHAR buf[MAX_PATH];
CHAR *pszURL;
HRESULT hr;
//
// Check usage.
//
if (argc != 2)
{
fprintf (stderr, "Usage: %s URL\n", argv[0]);
fprintf (stderr, "Eg %s c:\\nt\\private\\inet\\xml\\test\\channel.
cdf\n", argv[0]);
fprintf (stderr, "or %s http://ohserv/users/julianj/msnbc.
cdf\n", argv[0]);
exit (1);
}
//
// HACK if passed in a file name; expand if it doesn't look like
a URL.
//
if (CompareStringA(LOCALE_USER_DEFAULT, NORM_IGNORECASE, argv[1],
7, "http://", 7) == CSTR_EQUAL)
{
pszURL = argv[1];
}
else
{
pszURL = buf;
GetFullPathNameA(argv[1], MAX_PATH, pszURL, NULL);
}
hr = CoInitialize(NULL);
ASSERT(SUCCEEDED(hr));
//
// Create an empty XML document.
//
hr = CoCreateInstance(CLSID_XMLDocument, NULL, CLSCTX_INPROC_SERVER,
IID_IXMLDocument, (void**)&pDoc);
CHECK_ERROR (pDoc, "CoCreateInstance Failed");
//
// Synchronously create a stream on a URL.
//
hr = URLOpenBlockingStreamA(0, pszURL, &pStm, 0,0);
CHECK_ERROR(SUCCEEDED(hr) && pStm, "Couldn't open stream on URL")
//
// Get the IPersistStreamInit interface to the XML doc.
//
hr = pDoc->QueryInterface(IID_IPersistStreamInit, (void **)&pPSI);
CHECK_ERROR(SUCCEEDED(hr), "QI for IPersistStreamInit failed");
//
// Init the XML doc from the stream.
//
hr = pPSI->Load(pStm);
//CHECK_ERROR(SUCCEEDED(hr), "Couldn't load XML doc from stream");
if(SUCCEEDED(hr))
{
printf("%s : XML File is well formed \r\n",argv[0]);
}
else
{
// Print error information !
IXMLError *pXMLError = NULL ;
XML_ERROR xmle;
hr = pPSI->QueryInterface(IID_IXMLError, (void **)&pXMLError);
CHECK_ERROR(SUCCEEDED(hr), "Couldn't get IXMLError");
ASSERT(pXMLError);
hr = pXMLError->GetErrorInfo(&xmle);
SAFERELEASE(pXMLError);
CHECK_ERROR(SUCCEEDED(hr), "GetErrorInfo Failed");
printf("%s :", argv[0]);
wprintf(TEXT(" Error on line %d. Found %s while expecting
%s\r\n"),
xmle._nLine,
xmle._pszFound,
xmle._pszExpected);
SysFreeString(xmle._pszFound);
SysFreeString(xmle._pszExpected);
SysFreeString(xmle._pchBuf);
}
done: // Clean up.
//
// Release any used interfaces.
//
SAFERELEASE(pPSI);
SAFERELEASE(pStm);
SAFERELEASE(pDoc);
if (pszErr)
fprintf (stderr, "%s, last error %d\n", pszErr, GetLastError());
return 0;
}
Steve Lee (exhausted)
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