Getting the window title from a process name

Question

I am trying to write a program that can get the window title of a process. Before I describe the problem, here is the code:

#include <Windows.h>
#include <string>
#include <Psapi.h>
#include <algorithm>

std::string window_title;
std::string search_for;    

BOOL CALLBACK EnumWindowCallback(HWND hWindow, LPARAM param)
{
    if ( IsWindow( hWindow ) == TRUE )
    {
        DWORD pid = 0;

        if ( GetWindowThreadProcessId( hWindow, &pid ) != 0 )
        {
            HANDLE hProcess;
            hProcess = OpenProcess( PROCESS_ALL_ACCESS, FALSE, pid );
            if ( hProcess != 0 )
            {
                std::string path;
                CHAR name[MAX_PATH];
                GetModuleFileNameExA( hProcess, NULL, name, sizeof(name) / sizeof(CHAR) );
                path = name;
                unsigned int slash = path.find_last_of('\\');
                if ( slash != std::string::npos ){
                    std::string proc_name = path.substr( slash + 1, path.length() );
                    std::transform(proc_name.begin(), proc_name.end(), proc_name.begin(), ::tolower);
                    if ( proc_name == search_for )
                    {
                        CHAR finalTitle[MAX_PATH];
                        ZeroMemory( finalTitle, sizeof(finalTitle) );
                        SendMessageA( hWindow, WM_GETTEXT, (WPARAM)sizeof(CHAR)/sizeof(MAX_PATH), (LPARAM)finalTitle );
                        window_title = finalTitle;
                        return FALSE;
                    }
                }
            }
        }
    }
    return TRUE;
};

const char* __stdcall GetWinTitleByProcessName( const char* title )
{
    search_for = title;
    std::transform(search_for.begin(), search_for.end(), search_for.begin(), ::tolower);
    if ( EnumWindows( (WNDENUMPROC)EnumWindowCallback, 0 ) == FALSE )
    {
        return window_title.c_str();
    }

    return "NOTFOUND";
}

int WINAPI WinMain( HINSTANCE, HINSTANCE, LPSTR, int )
{
    MessageBoxA( NULL, GetWinTitleByProcessName("chrome.exe"), "Test", MB_OK);
}

The program works so far, until I want to get the actual title of the window. I tried GetWindowText and SendMessage, as shown here. Both methods return empty strings.

How can I get the window title?

Answer 1

The following code works for a similar problem. In my case I am looking for the windows handle of an application so that I can parent a dll. I identify the app by its caption. Its C++Builder code so some parts may be unfamiliar. I'll comment the differences I spot. The main one is the use of Application, I'm not sure what the non-Embarcadero equivalent is, but each running instance of code has an Application instance that manages the message loop and so on. I set my dll's Application->Handle to the calling apps hWnd to keep it off the taskbar, among other things. This code works on xp, vista 32 and win7 64.

   void HideDLL() {
      if (Application->Handle == 0) {
         SearchObject *so = new SearchObject();
         so->Caption = L"MyCallingApp";
         so->Handle = 0;
         EnumWindows((WNDENUMPROC)EnumWindowsProc, (long)so);
         Application->Handle = so->Handle;

         delete so;
      }

   }
   BOOL CALLBACK EnumWindowsProc(HWND hWnd, LPARAM lparam) {

      bool result;
      SearchObject *so = (SearchObject*)lparam;
      wchar_t *caption = new wchar_t[STR_DEFAULT];

      GetWindowTextW(hWnd, caption, STR_DEFAULT);
      // String is an Embarcadero type representing UnicodeString
      String Caption = caption;
      // Pos is a wrapper around strstr I think
      // the actual caption in my case is decorated with some other stuff
      // I only know that it will start with the name of the app
      if (Caption.Pos(so->Caption) > 0) {
         so->Handle = hWnd;
         result = false;
      } else {
         result = true;
      }
      delete caption;
      return result;
   }

Hope this helps.

Answer 2

It seems that (WPARAM)sizeof(CHAR)/sizeof(MAX_PATH) would return you zero, because sizeof(char) will be defenetly smaller then the max path, so you say to WinAPI that your variable has zero length, that's why it returns empty string to you. Specify there MAX_PATH value instead.