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HWND and HMODULE

Posted on 2008-06-16
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Last Modified: 2010-04-21
Hello
I have a code where, following is written for a GUI C/C++ app(VC++ .NET2003):

typedef struct tagAPPINFO {
   INT      iVersion;
   INT      iFiller;

   HWND     hAppInst;
   INT      iAppType;

   HWND     hWndFrame;
   HWND     hWndMDIClient;
   HWND     hWndToolbar;
   HWND     hWndStatbar;

   UINT     uMemBlocks;
   UINT     uMemBlockSize;

   char     szAppName  [MAXOBJNAME      + 2];
   char     szFileName [FILENAME_LENGTH + 2];
   char     szHelpFile [PATHNAME_LENGTH + 2];
   char     szPathName [PATHNAME_LENGTH + 2];
   BOOL     bDeltaMode;
   char     szSysPathName[PATHNAME_LENGTH + 2];
   } APPINFO;

static HMODULE hResourceModuke;
main()
{
APPINFO appinfo;
appinfo.hAppInst=hResourceModuke;
}

As a beginner, I would like to understand the purpose of HWND and HMODULE?

Regards
Sham
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Question by:sham_ibmgs
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19 Comments
 
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by:evilrix
Comment Utility
They are both handles. HWND is a window handle and HMODULE is a module handle. They are used to represent, internally to the WIN32 API, a windows and a module respectively. I'm sure you've already figure this out though, so is there anything specific you don't get?
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Author Comment

by:sham_ibmgs
Comment Utility
@evil: I already figure this out but, i would like to know, when shoule i use HWND and when should i use HMODULE from application perspective? and any difference between HWND and HMODULE?

am new to this kind of GUI programming!!!!!!

Regards
Sham
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Author Comment

by:sham_ibmgs
Comment Utility
@evil: What do u mean, when u say, "internally to the WIN32 API, a windows and a module respectively"


Regards
Sham
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Accepted Solution

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evilrix earned 100 total points
Comment Utility
I'm not sure what you mean in so far as when to use which. The documentation for a specific WIN32 API function will tell you whether it expects a handle to a window to a handle to a module. Generally, if the function is manipulating a window it will expect a HWND and if it is working with a module it will expect a HMODULE. For example, GetWindowText(), given a HWND to a window will give you the title for that window.

>> What do u mean, when u say, "internally to the WIN32 API, a windows and a module respectively"
The handle is just an opaque 32 bit value that is created by the API to reference an object. The relationship between this and the object it represents is managed by the API, you just need to pass it the handle to the object you wish to reference. For example, when you call CreateWindow, you'll get a handle to the window created. You can then reference that window using this handle. How this handle gets created or what it actually represents internally (it might be a pointer or an index into a table for example) to the API is not relevant to you (this is by design, you shouldn't need to know!), you just need to know that it references the window you've created.
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Author Comment

by:sham_ibmgs
Comment Utility
@evil: WHat about HMODULE? As u said HWND points to any window kind of object, To which type of object does HMODULE point?

Regards
Sham
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by:evilrix
Comment Utility
HMODULE represent a module... a module would be a DLL or an executable (EXE).
See the help for GetModuleHandle() and GetModuleFilename()
http://msdn.microsoft.com/en-us/library/ms683199(VS.85).aspx
http://msdn.microsoft.com/en-us/library/ms683197(VS.85).aspx
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Author Comment

by:sham_ibmgs
Comment Utility
@evil: what do u mean by term module here: "  if it is working with a module it will expect a HMODULE"

module mean a function?

Regards
Sham
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by:evilrix
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>> if it is working with a module it will expect a HMODULE
If the function is used to work with or manupulate a module, for example GetModuleFilename() returns the filename of a module (see my post above).
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Author Closing Comment

by:sham_ibmgs
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Done
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Author Comment

by:sham_ibmgs
Comment Utility
Hello

We have a code where  HMODULE object is asssigned to HWND object as below:

hAPPINST=hResourceModule;

hAPPINST is of type HWND and hResourceModule is of type HMODULE

Regards
Sham
 


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Author Comment

by:sham_ibmgs
Comment Utility
@evil: How can a module type handle be assigned to window type handle?

Regards
Sham
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by:evilrix
Comment Utility
Without seeing the code and the context I can't answer that... a HWND and a HMODULE are not related types, I presume there is a cast involved in this otherwise it shouldn't compile?
#include <windows.h>
 

int main()

{

	HWND hWnd = 0;

	HMODULE hModule = hWnd;

}
 

1>------ Build started: Project: testr, Configuration: Debug Win32 ------

1>Compiling...

1>main.cpp

1>main.cpp(6) : error C2440: 'initializing' : cannot convert from 'HWND' to 'HMODULE'

1>        Types pointed to are unrelated; conversion requires reinterpret_cast, C-style cast or function-style cast

1>Build log was saved at "file:BuildLog.htm"

1>testr - 1 error(s), 0 warning(s)

========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

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Author Comment

by:sham_ibmgs
Comment Utility
@evil: Here is the code
typedef struct tagAPPINFO {
   INT      iVersion;
   INT      iFiller;

   HWND     hAppInst;
   INT      iAppType;

   HWND     hWndFrame;
   HWND     hWndMDIClient;
   HWND     hWndToolbar;
   HWND     hWndStatbar;

   UINT     uMemBlocks;
   UINT     uMemBlockSize;

   char     szAppName  [MAXOBJNAME      + 2];
   char     szFileName [FILENAME_LENGTH + 2];
   char     szHelpFile [PATHNAME_LENGTH + 2];
   char     szPathName [PATHNAME_LENGTH + 2];
   BOOL     bDeltaMode;
   char     szSysPathName[PATHNAME_LENGTH + 2];
   } APPINFO;

static HMODULE hResourceModuke;
APPINFO  appInfo;
#define hAPPINST  appInfo.hAppInst  // this is header file  

int WINAPI TNGMain (LPSTR lpszCmdLine, ULONG TNGContext, int nCmdShow, HWND hParent)
{
/* clear application information structure */
   memset  (&appInfo, '\0', sizeof (APPINFO));

   /* save instance handle in structure */
   hAPPINST = hResourceModule;
   hWndParent = hParent;

   /* set other application information in structure */
   appInfo.iVersion      = iVERSION;
   appInfo.uMemBlocks    = NUMMEMBLOCKS;
   appInfo.uMemBlockSize = MEMBLOCKSIZE;
   strncpy(appInfo.szAppName,  szAPPNAME, MAXOBJNAME);
   strcpy(appInfo.szFileName, szFILENAME);
   strcpy(appInfo.szHelpFile, sz2DHELPFILE);

   /* register window classes if this is the first instance */
   if (!RegisterClasses (hAPPINST))
      return FALSE;
.
.
.
}

Regards
Sham

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Expert Comment

by:evilrix
Comment Utility
Are you sure that...

#define hAPPINST  appInfo.hAppInst  // this is header file  

...isn't being conditionally precompile to be either a HWND or a HMODULE depending upon build settings? Try changing hAPPINST = hResourceModule to be appInfo.hAppInst = hResourceModule and also, put a break point on this line to confirm the type is HWND. As you an see above, the types are not compatible under normal circumstances.
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Author Comment

by:sham_ibmgs
Comment Utility
am sure about it.

i wrote:

appInfo.hAppInst = hResourceModule; and compiled, it worked

Regards
Sham
 
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Author Comment

by:sham_ibmgs
Comment Utility
@evil: i placed another question with subject "wndclass and registerclass", Can u please look into that?

Regards
Sham
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Expert Comment

by:evilrix
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Then, I have to be honest, I don't know. I tested this in VS2005 and the types are not compatible.
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Author Comment

by:sham_ibmgs
Comment Utility
@evil: How do i know, whether, currently HWND/HMODULE pointer is pointed to some object or is NULL? can we write some debug statement?

Regards
Sham


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Expert Comment

by:evilrix
Comment Utility
>> How do i know, whether, currently HWND/HMODULE pointer is pointed to some object or is NULL?
Something like this maybe?
#include <windows.h>
 

int main()

{

	HWND hWnd = NULL;

	HMODULE hModule = NULL;
 

	if(NULL == hWnd) { /* it's null */ }

	if(NULL == hModule) { /* it's null */ }
 

	if(NULL != hWnd) { /* it's not null */ }

	if(NULL != hModule) { /* it's not null */ }

}

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