SetWindowsHookEx
in [Visual C]
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From: ama on 28 Dec 2005 12:17 hi here we go again with another question about system hooks... I compiled a dll and exported a function using a .DEF file. lets call it lib.dll . Inside my .exe i load the library and i call the exported call StartHook (see code below) Now the question i have is : What do i need to do to get notified for HCBT_CREATEWND for other applications ? Right now the only time CBTProc is called is for MY application only and of course i was hoping for a system wide hook so i can be notified when ANY window is created. Funny thing is i didnt tell SetWindowsHookEx to hook a specific Process. So what 's going on here? If this is default behavior whats the alternative. Here's part of the dll code : HHOOK gHhook = NULL; HINSTANCE gHinstance = NULL; BOOL APIENTRY DllMain(HANDLE hModule, DWORD ul_reason_for_call, LPVOID lpReserved) { gHinstance = (HINSTANCE)hModule; return TRUE; } LRESULT CALLBACK CBTProc(int nCode,WPARAM wParam,LPARAM lParam) { if( nCode < 0 ) return CallNextHookEx(gHhook, nCode, wParam, lParam); CallNextHookEx(gHhook, nCode, wParam, lParam); if( nCode == HCBT_CREATEWND ) ::PostMessage(ghTarget, WM_USER_WINDOWCREATED, wParam, 0); return 0; } //exported call HHOOK APIENTRY StartHook(HWND htarget) { if( ! gHinstance ) return 0; ghTarget = htarget; gHhook = SetWindowsHookEx(WH_CBT, (HOOKPROC)&CBTProc, gHinstance, 0); return gHhook; }
From: Igor Tandetnik on 28 Dec 2005 12:38 ama <a.m.a(a)videotron.ca> wrote: > I compiled a dll and exported a function using a .DEF file. > lets call it lib.dll . > > Inside my .exe i load the library and i call the exported call > StartHook (see code below) > > Now the question i have is : What do i need to do to > get notified for HCBT_CREATEWND for other applications ? Most likely, you already do. The problem is, each mapping of a DLL in a separate process has its own set of global variables. StartHook sets gHhook and ghTarget in the process it is called from, but these values are not visible in any other process. Your hook gets called from other processes but is unable to report this fact. See http://www.codeproject.com/dll/hooks.asp, the part that talks about #pragma data_seg. Note that you do _not_ want to share gHinstance, but you need to share gHhook and ghTarget. -- With best wishes, Igor Tandetnik With sufficient thrust, pigs fly just fine. However, this is not necessarily a good idea. It is hard to be sure where they are going to land, and it could be dangerous sitting under them as they fly overhead. -- RFC 1925
From: James Brown on 28 Dec 2005 12:39 comments inline "ama" <a.m.a(a)videotron.ca> wrote in message news:pMzsf.123974$0p5.1325182(a)wagner.videotron.net... > hi > > here we go again with another question about system hooks... > > I compiled a dll and exported a function using a .DEF file. > lets call it lib.dll . > > Inside my .exe i load the library and i call the exported call > StartHook (see code below) > > Now the question i have is : What do i need to do to > get notified for HCBT_CREATEWND for other applications ? > > Right now the only time CBTProc is called is for MY application > only and of course i was hoping for a system wide hook so i can > be notified when ANY window is created. > > Funny thing is i didnt tell SetWindowsHookEx to hook a specific Process. > So what 's going on here? If this is default behavior whats the > alternative. > > Here's part of the dll code : > > HHOOK gHhook = NULL; > HINSTANCE gHinstance = NULL; You *must* place your gHhook handle inside a shared section. You haven't made the mistake that most make by failing to initialize it to NULL though (failure to do this means it won't get placed in your new section). #pragma data_seg(".shared") #pragma comment(linker, "/section:.shared,rws") HHOOK gHook = NULL; HWND ghTarget = NULL; #pragma data_seg() > BOOL APIENTRY DllMain(HANDLE hModule, DWORD ul_reason_for_call, LPVOID > lpReserved) > { > gHinstance = (HINSTANCE)hModule; > return TRUE; > } > > LRESULT CALLBACK CBTProc(int nCode,WPARAM wParam,LPARAM lParam) > { > if( nCode < 0 ) > return CallNextHookEx(gHhook, nCode, wParam, lParam); > > CallNextHookEx(gHhook, nCode, wParam, lParam); > > if( nCode == HCBT_CREATEWND ) > ::PostMessage(ghTarget, WM_USER_WINDOWCREATED, wParam, 0); > > return 0; > } > > //exported call > HHOOK APIENTRY StartHook(HWND htarget) > { > if( ! gHinstance ) > return 0; > > ghTarget = htarget; > gHhook = SetWindowsHookEx(WH_CBT, (HOOKPROC)&CBTProc, gHinstance, 0); > > return gHhook; > } > > > The docs are very clear about global hooking. If you pass 0 (NULL) as the last parameter to SetWindowsHookEx then your hook is associated with all threads running under the current desktop (and therefore will be automatically injected into any process which has it's threads hooked) When your CBTProc executes it will be in the context of another process. So you will need to devise some mechanism to communicate back to the "original" process. I see you are using PostMessage for this matter. This is a good choice, but be careful that you also place your "ghTarget" window-handle in the ".shared" section, otherwise this window-handle will not be accessible to other processes which map your DLL into their address spaces. James -- www.catch22.net Free Win32 Source and Tutorials
From: ama on 28 Dec 2005 21:53 > Most likely, you already do. The problem is, each mapping of a DLL in a > separate process has its own set of global variables. StartHook sets > gHhook and ghTarget in the process it is called from, but these values are > not visible in any other process. Your hook gets called from other > processes but is unable to report this fact. > Ok thanks. I tried all that too : #pragma data_seg(".shared") HHOOK gHhook = NULL; HINSTANCE gHinstance = NULL; UINT WM_USER_WINDOWCREATED = (WM_USER+100); #pragma data_seg() #pragma comment( linker, "/SECTION:.shared,RWS" ) before and after posting the first question. I tried everything in case there's a flaw in the docs or with winxp sp2 etc... Since noone pointed me with errors in the code posted in the previous post and if the code above is ok ill assume the problem is something wrong with windows on my PC... lets call it voodoo.. thanks anyways.
From: Alexander Grigoriev on 28 Dec 2005 23:41
Read the thread again. You don't need to share gHinstance, but you need ghTarget. "ama" <a.m.a(a)videotron.ca> wrote in message news:ScIsf.131591$0p5.1588261(a)wagner.videotron.net... > >> Most likely, you already do. The problem is, each mapping of a DLL in a >> separate process has its own set of global variables. StartHook sets >> gHhook and ghTarget in the process it is called from, but these values >> are not visible in any other process. Your hook gets called from other >> processes but is unable to report this fact. >> > > Ok thanks. > > I tried all that too : > > #pragma data_seg(".shared") > HHOOK gHhook = NULL; > HINSTANCE gHinstance = NULL; > UINT WM_USER_WINDOWCREATED = (WM_USER+100); > #pragma data_seg() > #pragma comment( linker, "/SECTION:.shared,RWS" ) > > before and after posting the first question. I tried everything > in case there's a flaw in the docs or with winxp sp2 etc... > > Since noone pointed me with errors in the code posted > in the previous post and if the code above is ok > ill assume the problem is something wrong with windows > on my PC... lets call it voodoo.. > > thanks anyways. > > > > |