Sample use of the WM_COPYDATA message.
This is a single-program sample, created in Visual Studio as a Windows Desktop Applicaiton. It needs to be executed twice. The first execution will be the receiver. The second execution will be the sender of a string. Each time the Send button is pressed a string with the current time is sent to the other instance.
The data is sent using:
// Format the time into a string
TCHAR timeString[30];
time_t secs = time(0);
struct tm local;
localtime_s(&local, &secs);
swprintf(timeString, sizeof(timeString), L"%02d:%02d:%02d", local.tm_hour, local.tm_min, local.tm_sec);
// Send the string
COPYDATASTRUCT cds{};
cds.dwData = 1;
cds.cbData = (wcslen(timeString)+1)*sizeof(TCHAR);
cds.lpData = (PVOID)timeString;
SendMessage(OtherhWnd, WM_COPYDATA, NULL, (LPARAM)&cds);
The data is received using:
COPYDATASTRUCT *pMessageCDS = (PCOPYDATASTRUCT)lParam;
// first save the string
pSavedString = (TCHAR*)malloc(pMessageCDS->cbData);
memcpy_s(pSavedString, pMessageCDS->cbData, pMessageCDS->lpData, pMessageCDS->cbData);
// now use it now and later
SetDlgItemTextW(hWnd, IDC_MESSAGE_EDIT, pSavedString);