Question

I am new to inter process communication and need some help. I want to be able to send a string from a C++ program to a C# program. My problem is that the resultant string is gibberish. Here is my code:

Sending program (C++):

void transmitState(char* myStr) {      HWND hWnd = ::FindWindow(NULL, _T('myApp v.1.0'));     if (hWnd)     {         COPYDATASTRUCT cds;         ::ZeroMemory(&cds, sizeof(COPYDATASTRUCT));         cds.dwData = 0;         cds.lpData = (PVOID) myStr;         cds.cbData = strlen(myStr) + 1;          ::SendMessage(hWnd, WM_COPYDATA, NULL, (LPARAM)&cds);     } }    

And the receiving program (C#) (I have already overridden the WndProc):

private void OnCopyData(ref Message m) {     COPYDATASTRUCT cds = new COPYDATASTRUCT();     cds = (COPYDATASTRUCT)Marshal.PtrToStructure(m.LParam, typeof(COPYDATASTRUCT));      String myStr;     unsafe     {         myStr = new String((char*) cds.lpData);     }      label1.Text = myStr; } 

Answer 1

char* in C++ is ANSI character string (usually one byte per character), char* in C# is Unicode character string (like WCHAR* – two bytes per character).

You in fact reinterpret_cast from char* to WCHAR*. This won’t work. Use MultiByteToWideChar() on C++ side to convert.