Robust, simple (and fast) interprocess communication in C++ on Windows - c++

Question

I am developing a plug-in for two 3rd party programs: A and B in C++ on Windows (7) and need a robust, relatively simple (and fast) way to communicate between the two programs.
The communication is one way: based on user interaction in program A I want my plug-in inside program A to send a signal that ends up calling a function inside my plug-in in program B.
The protocol is simple. This is the signature of the receiving function inside my plug-in in B:
struct XYZ {
double x, y, z;
}
void polyLineSelected(long id, std::vector<XYZ> & points);
How would you recommend to do this?

Answer 1

By far the easiest way to implement one-way communication on Windows is to send a WM_COPYDATA message. It takes a COPYDATASTRUCT parameter to move arbitrary data from one application to another.
For your specific example an implementation of the sender would look like this:
// Declare symbolic constants to identify data
enum DataType {
DataType_Points
};
// Declare struct to hold compound data
struct IPCData {
long id;
XYZ pts[];
};
// Allocate buffer
const size_t bufferSize = offsetof(IPCData, pts[points.size()]);
vector<char> buffer(bufferSize);
IPCData* pData = reinterpret_cast<IPCData*>(&buffer[0]);
// Fill the buffer
pData->id = 42;
copy(points.begin(), points.end(), &pData->pts[0]);
// Prepare COPYDDATASTRUCT
COPYDATASTRUCT cds = { 0 };
cds.dwData = DataType_Points; // Can be used by the receiver to identify data
cds.cbData = bufferSize;
cds.lpData = pData;
// Send the data
SendMessage(hWndRecv, WM_COPYDATA,
(WPARAM)hWndSender,
(LPARAM)(LPVOID)&cds);