This document describes two techniques for inter-process communication (IPC) in Windows: using the clipboard and using data copy. It explains how to share data between processes using the Windows clipboard API functions like OpenClipboard(), SetClipboardData(), and CloseClipboard(). It also explains how to send data between processes using the WM_COPYDATA message, a COPYDATASTRUCT structure, and the SendMessage() API function. Both techniques allow sharing data between processes on the same computer.

1. Using Clipboard and Data Copy
for IPC in Windows
Describes using two simplest techniques of
IPC in Windows: Clipboard and Data Copy
Compiled By:
B. Vinoth Raj
Senior Software Engineer
Mindfire Solutions

2. IPC using Clipboard
 Loosely coupled exchange medium
 For data exchange, applications agree on the data format
 Data can be shared between processes on same computer
or unrelated processes on a network
 Windows API functions used are:
OpenClipboard(), EmptyClipboard(), SetClipboardData(),
CloseClipboard() and GetClipboardData()

3. IPC using Clipboard (cont.)
 Before copying data one opens the clipboard using
OpenClipboard()
 Emtpy the clipboard using EmptyClipboard() to clear
existing contents
 Set data using SetClipboardData() function in a specified
format
 Close the clipboard using CloseClipboard() function
 Read the data using GetClipboardData() function in
another process

4. IPC using Clipboard (cont.)
 Before copying data one opens the clipboard using
OpenClipboard()
CString sData(_T("Sample data"));
HGLOBAL hMem = GlobalAlloc(GMEM_MOVEABLE | GMEM_DDESHARE, (sData.GetLength() + 1) *
sizeof(WCHAR)); memcpy(GlobalLock(hMem), sData, sData.GetLength() * sizeof(WCHAR));
GlobalUnlock(hMem);
OpenClipboard();
EmptyClipboard();
SetClipboardData(CF_UNICODETEXT, hMem);
CloseClipboard();
· GlobalAlloc function is used because the system takes
ownership of the memory passed to the clipboard

5. IPC using Data Copy
 Use WM_COPYDATA windows message to share data
 SendMessage() API function used to send data
 COPYDATASTRUCT structure used to send data
SendMessage(hwnd, // Handle to destination window
WM_COPYDATA, // Message to send to destination window
(WPARAM)wparam, // Handle to window passing the data
(LPARAM)lparam); // Data (pointer to COPYDATASTRUCT)
 The data sent is read-only for the receiving application
 Works only for processes running on same computer

6. IPC using Data Copy (cont.)
 Code Usage
CString sMsg(_T("Hello this message is from WM_COPYDATA"));
COPYDATASTRUCT data;
data.dwData = 1;
data.cbData = sMsg.GetLength()*sizeof(WCHAR);
data.lpData = &sMsg;
HWND destWnd = FindWindow(_T("WinClassName"), _T("WindowName"));
SendMessage(destWnd, WM_COPYDATA, (WPARAM)(HWND)hwnd, (LPARAM)(LPVOID)&data);
Receiving application should implement the WM_COPYDATA message in its message loop:
case WM_COPYDATA:
PCOPYDATASTRUCT pcData;
pcData = (PCOPYDATASTRUCT) lParam;
CString* sRecvMsg = pcData->lpData;
break;

7. Thanks!