ipc - Why dwData = new IntPtr(0) would work in WM_COPYDATA (c# visual studio 2015) -

when set copydatastruct, set {

dwdata = new intptr(0) 

} , , sender send message receiver. however, when tried {

dwdata = new intptr(xxothernumbersxxx) 

} , not work. can explain me dwdata doing here? thanks!

(p.s. newbie software engineer passionate heart learn, gentle on ratings.... plz.....)

here source code sender in c# :

using system; using system.diagnostics; using system.runtime.interopservices; using system.windows.forms;  // application sender // made work receiver made in pascal xxxxxx  // receiver located @  // "k:\xxxxxxxxxxx" //  // application meant send string "hello world" receiver // if successful, receiver appear on screen: // //                 wm_copydata from: 3819 //                 received string "hello world!" @ 6/3/2015 // // application: // 1. put "hello world!" message data structure called "copydatastuct" // 2. find receiver app title "receivermainform" , class "treceivermainform" (debug window: pop-up window should show non-zero integers) // 3. send message in copydatastruct through wm_copydata code receiver  namespace findnotepad {     class program     {       //include sendmessage         [dllimport("user32.dll")]         public static extern int sendmessage(intptr hwnd, int umsg, int wparam, ref copydatastruct lparam);          //include sendmessage         [dllimport("user32.dll")]         public static extern intptr findwindow(string lpszclass, string lpszwindow);          //this constant indicating window want send text message         const int wm_copydata = 0x004a;         static void main(string[] args)         {              // ---------------- 1. set message sent -----------------------             //put "hello world!" message data structure called "copydatastuct"             string msg = "hello world!";             var cds = new copydatastruct             {                 dwdata = new intptr(0),                 cbdata = msg.length + 1,                 lpdata = msg             };             // ---------------- 2. find receiver application window -----------------------             intptr receiverhandle = findwindow("treceivermainform", "receivermainform");              // debug window pop-up             messagebox.show(receiverhandle.tostring());               // ---------------- 3. send message receiver -----------------------             try             {                 sendmessage(receiverhandle, wm_copydata, 3819, ref cds);                 // receiverhandle: handle receiver window                 // wm_copydata: application sends wm_copydata message pass data application                 // 3819: handle of sender application, preset integer can work. distinguish sender sends message on receiver                 // ref cds: data structure contains message sent.             }             catch (exception ex)             {                 messagebox.show(ex.message);             }         }         //used wm_copydata string messages         public struct copydatastruct         {             //dwdata             //the data passed receiving application.             public intptr dwdata;             // cbdata             // size, in bytes, of data pointed lpdata member.             public int cbdata;             // lpdata             // data passed receiving application. member can null.             public string lpdata;         }     } }