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

EnumWindows() and EnumChildWindows() would be a good starting point.

EnumWindows() / EnumChildWindows() / GetWindow()
FindWindow[Ex]()

gg

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.

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!!!

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

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.


:(

Looks like you need to link with user32.lib.

Thanks Ken :)