Windows handles

This is a discussion on Windows handles within the Windows Programming forums, part of the Platform Specific Boards category; Hi, I'm trying to write a program that will automate a process for me based on the text output in ...

  1. #1
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    Windows handles

    Hi,

    I'm trying to write a program that will automate a process for me based on the text output in a scroll window belonging to another app. The first step is that I need to be able to get the handle for the window in question but I'm not sure how to do this.

    So, can someone tell me how to get a list of all the current active windows ?

    Thanks,
    Marc

  2. #2
    It's full of stars adrianxw's Avatar
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    EnumWindows() and EnumChildWindows() would be a good starting point.
    Wave upon wave of demented avengers march cheerfully out of obscurity unto the dream.

  3. #3

  4. #4
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    That's great, thanks.

    While I'm at it, once I have these handles, can I send messages to any child window of one of these parent windows belonging to another app ? For example, could I even register a mouse button press on a button belonging to the window just by sending it the appropriate message ?

    Apologies if these are basic questions - I'm an experienced coder but just not to windows.

  5. #5
    Handy Andy andyhunter's Avatar
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    You would use the SendMessage function, its prototype is:

    SendMessage(HWND hwnd, UINT message, WPARAM, LPARAM)

    Below are 2 examples one basic which writes characters to the notepad window and one slightly more general which was originally provided by Lucky.

    Basic:
    Code:
    #include <windows.h>
    #include <stdio.h>
    
    int main(void)
    {
    	char chars[] = "abc";
    	HWND hwndNotepad, hwndChild; 
    	
                    //query for notepad
    	hwndNotepad = FindWindow(NULL, "Untitled - Notepad");
    	
    	if(hwndNotepad == NULL)
    	{
    		printf("error! HWND notepad = NULL\n");
    		return(0);
    	}
    
    	//query for the child window(edit control)
                    hwndChild = GetWindow(hwndNotepad, GW_CHILD);
    
                    //send our message
    	if(!(hwndChild == NULL)) {
    		for(int a = 0; a<4; a++) {
    
    			SendMessage(hwndChild, WM_CHAR, (WPARAM)chars[a], 1);
    		}
    	}
    
    	return 0;
    }
    General(provided by Lucky):
    Code:
    #include <windows.h>
    #include <tchar.h>
    
    // use some default text if none is supplied on the command line
    static LPCTSTR DEFAULT_MSG = _T("This text was automatically inserted.");
    
    // a container to pass to arguments - the string and it's length
    struct StringMsg {
      int nLength;
      LPCTSTR pszText;
    };
    
    // iteratively process each child window of the pass HWND
    BOOL CALLBACK EnumChildProc(HWND hwnd, LPARAM lParam) {
      // first we determine the classname 
      TCHAR szClassName[32];
      GetClassName(hwnd, szClassName, 32);
    
      // if it is not an edit window, we'll just continue with
      // the next child window
      if (_tcsncmpi(szClassName, _T("EDIT"), 4) != 0)
        return TRUE;
    
      // otherwise we auto-type something into the edit window and
      // cease the enumeration  
      StringMsg *pMsg = (StringMsg*)lParam;
      for (int i = 0; i < pMsg->nLength; ++i)
        SendMessage(hwnd, WM_CHAR, pMsg->pszText[i], 0);
    
      return FALSE;
    }
    
    // this is called for every top-most HWND
    BOOL CALLBACK EnumWindowsProc(HWND hwnd, LPARAM lParam) {
      TCHAR szClassName[32];
      GetClassName(hwnd, szClassName, 32);
    
      // determine if it is our target application window
      if (_tcsncmpi(szClassName, _T("NOTEPAD"), 7) == 0)
        // if it is, we'll enumerate it's children and let that
        // enumeration handle finding the target control and doing
        // our dirty work, then stop looking
        if (!EnumChildWindows(hwnd, EnumChildProc, lParam))
          return FALSE;
    
      // otherwise we just keep looking
      return TRUE;
    }
    
    // program entry point
    // pass a string on the command line or let the default text
    // be used 
    int _tmain(int argc, TCHAR **argv) {
      StringMsg sm;
    
      // argument? use it  
      if (argc > 1) {
        sm.nLength = _tcslen(argv[1]);
        sm.pszText = argv[1];
      }
      // none? use ours
      else {
        sm.nLength = _tcslen(DEFAULT_MSG);
        sm.pszText = DEFAULT_MSG;
      }  
    
      // enumerate all the top-level windows
      EnumWindows(EnumWindowsProc, (LPARAM)&sm);  
    
      return 0;
    }
    Happy Coding!!!
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    Such pointless tricks ceased to be interesting or useful when we came down from the trees and started using higher level languages. - Salem

  6. #6
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    Thanks,

    I've started using SendMessage ( ) with EM_GETLINECOUNT and EM_GETLINE and that seems to be retrieving the text for me.

    I plan to just keep a count of the line count when I last read and the new line count to get new content added to the window.

    Much appreciated,
    Marc

  7. #7
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    The basic example above isn't working. I am using Pelles C for Windows as a compiler.
    It compiles ok but when I tell it to build I get errors:

    Building window.exe.
    POLINK: error: Unresolved external symbol '__imp__FindWindowA'.

    POLINK: error: Unresolved external symbol '__imp__GetWindow'.

    POLINK: error: Unresolved external symbol '__imp__SendMessageA'.

    POLINK: fatal error: 3 unresolved external(s).

    *** Error code: 1 ***
    Done.



  8. #8
    erstwhile
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    Looks like you need to link with user32.lib.
    CProgramming FAQ
    Caution: this person may be a carrier of the misinformation virus.

  9. #9
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    Thumbs up

    Thanks Ken

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