BorlandTalk.com Borland discussion newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Retrieving another application data          BorlandTalk.com Forum Index -> C++ Builder (Language C++) View previous topic :: View next topic   Author Message Volodymyr Novikov Guest Posted: Sun Aug 21, 2005 6:16 pm    Post subject: Retrieving another application data Hello All. I am writing an application which has to communicate with another application by retrieving members of data structure within the application. What I am doing basically is: 1.Define structure same way as it defined in another application. 2. Receive from another application address of the structure using socket connection. 3. Assign received address to a pointer to the structure. Now comes trouble: when I try to access structure member like ptrStruct->Member I am as expected getting an Address violation exception. Is there any way of getting around this? Thanks in advance and sorry if the question is too stupid. Regards. Back to top Michel Leunen Guest Posted: Sun Aug 21, 2005 7:11 pm    Post subject: Re: Retrieving another application data Volodymyr Novikov wrote: Quote: I am writing an application which has to communicate with another application by retrieving members of data structure within the application. What I am doing basically is: 1.Define structure same way as it defined in another application. 2. Receive from another application address of the structure using socket connection. 3. Assign received address to a pointer to the structure. Now comes trouble: when I try to access structure member like ptrStruct->Member I am as expected getting an Address violation exception. This won't work because each process is executed in its own memory space. Instead, look at CreateFileMapping()/OpenFilemapping() or use your socket but send the data instead of the address of the structure. There are other ways like pipes for instance to do this job. Michel -- ---------------------------------------- Michel Leunen mailto: see my homepage. C++Builder, BCC5.5.1 Web site: http://www.leunen.com/ ---------------------------------------- Back to top Duane Hebert Guest Posted: Sun Aug 21, 2005 8:03 pm    Post subject: Re: Retrieving another application data "Volodymyr Novikov" <v.novikov (AT) sympatico (DOT) ca> wrote Quote: Hello All. I am writing an application which has to communicate with another application by retrieving members of data structure within the application. What I am doing basically is: 1.Define structure same way as it defined in another application. 2. Receive from another application address of the structure using socket connection. 3. Assign received address to a pointer to the structure. Now comes trouble: when I try to access structure member like ptrStruct->Member How about sending/receiving the data from the structure and constructing a new one on the receiving end with that data? We usually add a ctor for the struct that takes a string that's built from socket data. This way there's a local copy (adress space wise) of the structure. Back to top JD Guest Posted: Sun Aug 21, 2005 10:18 pm    Post subject: Re: Retrieving another application data "Volodymyr Novikov" <v.novikov (AT) sympatico (DOT) ca> wrote: Quote: [...] What I am doing basically is: [...] The AV is thrown because one application is attempting to access memory that is owned by another application. Use WM_COPYDATA instead. ~ JD Back to top Volodymyr Novikov Guest Posted: Sun Aug 21, 2005 11:16 pm    Post subject: Re: Retrieving another application data Yes, I considered this possibility and disregarded it as too slow (data send thru socket takes ~100ms, which is too slow for my case). Would be more than OK in 99% of cases though. Thanks anyway. "Duane Hebert" <spoo (AT) flarn2 (DOT) com> wrote Quote: "Volodymyr Novikov" <v.novikov (AT) sympatico (DOT) ca> wrote in message news:4308c504 (AT) newsgroups (DOT) borland.com... Hello All. I am writing an application which has to communicate with another application by retrieving members of data structure within the application. What I am doing basically is: 1.Define structure same way as it defined in another application. 2. Receive from another application address of the structure using socket connection. 3. Assign received address to a pointer to the structure. Now comes trouble: when I try to access structure member like ptrStruct->Member How about sending/receiving the data from the structure and constructing a new one on the receiving end with that data? We usually add a ctor for the struct that takes a string that's built from socket data. This way there's a local copy (adress space wise) of the structure. Back to top Remy Lebeau (TeamB) Guest Posted: Mon Aug 22, 2005 5:14 pm    Post subject: Re: Retrieving another application data "Volodymyr Novikov" <v.novikov (AT) sympatico (DOT) ca> wrote Quote: 2. Receive from another application address of the structure using socket connection. 3. Assign received address to a pointer to the structure. You cannot do that. Each application has its own memory address space that is separate from every other application. A memory address in one application WILL NOT be a valid memory address in another application. To do what you are asking for, you need to send the actual data members that are contained inside the structure. You cannot send just a pointer to the structure itself. On the receiving end, it reads the data and uses it to populate a local instance of the structure. Quote: Now comes trouble: when I try to access structure member like ptrStruct->Member I am as expected getting an Address violation exception. Of course, because what you are trying to do is illegal. Applications cannot access each other's address space. Gambit Back to top Remy Lebeau (TeamB) Guest Posted: Mon Aug 22, 2005 5:23 pm    Post subject: Re: Retrieving another application data "Volodymyr Novikov" <v.novikov (AT) sympatico (DOT) ca> wrote Quote: Yes, I considered this possibility and disregarded it as too slow (data send thru socket takes ~100ms, which is too slow for my case). Then your requirement is too restrictive, because sending the actual data is the only way to send anything over a socket. Also, you are probably not using the socket correctly in the first place, because you should be able to send data much faster than 100ms, especially if the two applications are on the same machine. But you did not show any of your actual code, so there is no way to know if you are managing the socket correctly. Even so, if the socket is still too slow for you, then using a socket is not the best choice for your application in the first place. Gambit Back to top Volodymyr Novikov Guest Posted: Mon Aug 22, 2005 11:46 pm    Post subject: Re: Retrieving another application data "Remy Lebeau (TeamB)" <no.spam (AT) no (DOT) spam.com> wrote Quote: "Volodymyr Novikov" <v.novikov (AT) sympatico (DOT) ca> wrote in message news:43090b59$1 (AT) newsgroups (DOT) borland.com... Yes, I considered this possibility and disregarded it as too slow (data send thru socket takes ~100ms, which is too slow for my case). Then your requirement is too restrictive, because sending the actual data is the only way to send anything over a socket. Also, you are probably not using the socket correctly in the first place, because you should be able to send data much faster than 100ms, especially if the two applications are on the same machine. But you did not show any of your actual code, so there is no way to know if you are managing the socket correctly. Even so, if the socket is still too slow for you, then using a socket is not the best choice for your application in the first place. Gambit This is a piece of testcode to mesure time from request to reply. Time delay includes also reply callback procedure within another application, which is very simple hence may be neglected. TclientSocket is used on both sides: //--------------------------------------------------------------------------- void __fastcall TForm1::Button3Click(TObject *Sender) { t1=timeGetTime(); CSocket1->Socket->SendText(Edit1->Text+"rn"); } //--------------------------------------------------------------------------- void __fastcall TForm1::CSocket1Read(TObject *Sender, TCustomWinSocket *Socket) { ch=Socket->ReceiveText(); lastline=ch; Bar1->Panels->Items[1]->Text=IntToStr(timeGetTime()-t1); Bar1->Panels->Items[0]->Text=ch; //--------------------------------------------------------------------------- Propagation time in my case lies within 40-150ms. Thanks, Vladimir. Back to top Duane Hebert Guest Posted: Mon Aug 22, 2005 11:56 pm    Post subject: Re: Retrieving another application data "Volodymyr Novikov" <v.novikov (AT) sympatico (DOT) ca> wrote Quote: This is a piece of testcode to mesure time from request to reply. Time delay includes also reply callback procedure within another application, which is very simple hence may be neglected. TclientSocket is used on both sides: //--------------------------------------------------------------------------- void __fastcall TForm1::Button3Click(TObject *Sender) { t1=timeGetTime(); CSocket1->Socket->SendText(Edit1->Text+"rn"); } //--------------------------------------------------------------------------- void __fastcall TForm1::CSocket1Read(TObject *Sender, TCustomWinSocket *Socket) { ch=Socket->ReceiveText(); lastline=ch; Bar1->Panels->Items[1]->Text=IntToStr(timeGetTime()-t1); Bar1->Panels->Items[0]->Text=ch; //--------------------------------------------------------------------------- Propagation time in my case lies within 40-150ms. Thanks, Vladimir. I assume that CSocket1Read() is an event. If this is so, you're timing is based on when the event loop updates more than the time it takes to send the data. You may want to try polling for data directly. You can normally send quite a bit of data through a socket in 150ms. If this is a strictly windows application, you may also want to look at some of the other ideas suggested in this thread. Back to top Volodymyr Novikov Guest Posted: Mon Aug 22, 2005 11:58 pm    Post subject: Re: Retrieving another application data "Remy Lebeau (TeamB)" <no.spam (AT) no (DOT) spam.com> wrote Quote: "Volodymyr Novikov" <v.novikov (AT) sympatico (DOT) ca> wrote in message news:4308c504 (AT) newsgroups (DOT) borland.com... 2. Receive from another application address of the structure using socket connection. 3. Assign received address to a pointer to the structure. You cannot do that. Each application has its own memory address space that is separate from every other application. A memory address in one application WILL NOT be a valid memory address in another application. To do what you are asking for, you need to send the actual data members that are contained inside the structure. You cannot send just a pointer to the structure itself. On the receiving end, it reads the data and uses it to populate a local instance of the structure. Now comes trouble: when I try to access structure member like ptrStruct->Member I am as expected getting an Address violation exception. Of course, because what you are trying to do is illegal. Applications cannot access each other's address space. Gambit I gave up socket connection and now using WM_COPYDATA Message which works OK for me. ....And still where must be a way of direct accessing another's application data which is of course illegal from the viewpoint of Windows i.e hacker stuff mostly. Thanks everybody fir help. Regards, Vladimir. Back to top Remy Lebeau (TeamB) Guest Posted: Tue Aug 23, 2005 6:52 am    Post subject: Re: Retrieving another application data "Volodymyr Novikov" <v.novikov (AT) sympatico (DOT) ca> wrote Quote: This is a piece of testcode to mesure time from request to reply. That code is going to be slow because you are using the socket in non-blocking mode, which means the speed of the processing is directly related to the speed in which the application can process messages from the main message queue. If you change to using a blocking socket instead, and put in it a worker thread, you are likely to see a bit of a speed increase, both in GUI responsiveness and in data processing. Quote: TclientSocket is used on both sides: Two client sockets cannot communicate with each other. One of the applications has to be using a server socket that the client socket then connects to. Gambit Back to top Remy Lebeau (TeamB) Guest Posted: Tue Aug 23, 2005 6:55 am    Post subject: Re: Retrieving another application data "Volodymyr Novikov" <v.novikov (AT) sympatico (DOT) ca> wrote Quote: ...And still where must be a way of direct accessing another's application data The OS strictly prohibits that. That is why each application has its own address space to begin with - specifcally so that application cannot access each other's memory directly. Also so that if one application crashes, it doesn't (usually) take down other applications with it. The only application that can access another application's memory is a debugger, for obvious reasons. Gambit Back to top Alan Bellingham Guest Posted: Tue Aug 23, 2005 9:51 am    Post subject: Re: Retrieving another application data "Volodymyr Novikov" <v.novikov (AT) sympatico (DOT) ca> wrote: Quote: ...And still where must be a way of direct accessing another's application data which is of course illegal from the viewpoint of Windows i.e hacker stuff mostly. There are ways. They involve rewriting chunks of the operating system. 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