C / C++ / MFC

18-Nov-02 17:51

Hi guys,

I'm sure there are some java gurus out there who also know c++. Anyone know the answer to the following:

In C++, I declare functions such as:

void PassInAConstantReference(const Object& o);
void PassInAModifiableReference(Object& o);
void PassInACopy(Object o);

In java, so far I only see:

void PassInAModifiableReference(Object o);

Any equivalent of the above C++ functions in Java? Wink | ;)

Cheers,

swine

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Christian Graus18-Nov-02 17:58

18-Nov-02 17:58

In Java there are no pointers, and no const, and I believe everything is passed by reference.

Christian

No offense, but I don't really want to encourage the creation of another VB developer. - Larry Antram 22 Oct 2002

Hey, at least Logo had, at it's inception, a mechanical turtle. VB has always lacked even that... - Shog9 04-09-2002

Again, you can screw up a C/C++ program just as easily as a VB program. OK, maybe not as easily, but it's certainly doable. - Jamie Nordmeyer - 15-Nov-2002

Swinefeaster18-Nov-02 18:00

18-Nov-02 18:00

So you can only do it non-const and by reference? That sux...

swine

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Christian Graus18-Nov-02 18:12

18-Nov-02 18:12

Yes, yes it does. I've been whining about the lack of const in C# for months, and the common response is that Java is the same, that's why I know. I've never coded in Java, so someone may correct me, but I'm pretty sure, and I'm *very* sure that it sucks.

Christian

No offense, but I don't really want to encourage the creation of another VB developer. - Larry Antram 22 Oct 2002

Hey, at least Logo had, at it's inception, a mechanical turtle. VB has always lacked even that... - Shog9 04-09-2002

Again, you can screw up a C/C++ program just as easily as a VB program. OK, maybe not as easily, but it's certainly doable. - Jamie Nordmeyer - 15-Nov-2002

Swinefeaster18-Nov-02 18:16

18-Nov-02 18:16

lol

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S van Leent19-Nov-02 7:31

S van Leent

19-Nov-02 7:31

Bunch of criminals, Java does have const, namely final!

LPCTSTR Dutch = TEXT("Double Dutch Smile | :)

");

Swinefeaster18-Nov-02 18:24

18-Nov-02 18:24

so then, would the following work:

public boolean receiveAndUnmarshallInvoke(CRmiInvokeMessage InvokeMessage,
ServerSocket ListenSocket, Socket TheClientSocket)
{
boolean success = false;

if(TheSocket == null)
{
System.err.println("Null TheSocket passed in CRmiCommunicator.receiveAndUnmarshallInvoke().");
}
else
{
TheClientSocket = ListenSocket.accept();
}

return success;
}

Err, as in, the caller passes in a local client socket object for the TheClientSocket parameter, and when the function returns, the caller's local object is now the accepted client socket?

Thanks,

swine

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Christian Graus18-Nov-02 18:59

18-Nov-02 18:59

I'm sorry, I could not say, but it should not be hard to design a test to see.

Christian

No offense, but I don't really want to encourage the creation of another VB developer. - Larry Antram 22 Oct 2002

Hey, at least Logo had, at it's inception, a mechanical turtle. VB has always lacked even that... - Shog9 04-09-2002

Again, you can screw up a C/C++ program just as easily as a VB program. OK, maybe not as easily, but it's certainly doable. - Jamie Nordmeyer - 15-Nov-2002

Joaquín M López Muñoz18-Nov-02 19:57

Joaquín M López Muñoz

18-Nov-02 19:57

...the caller's local object is now the accepted client socket?

No. In Java, primitive types (ints, floats) are passed by value, anything else (objects whose type begin with a capital letter, if you want a mnemonic) is passed as if with a hidden pointer. In your particular case, picturing a '*' at appropriate places will help you realize TheClientSocket won't hold the newly accepted socket on return:

// Not quite Java!
public boolean receiveAndUnmarshallInvoke(CRmiInvokeMessage * InvokeMessage,
ServerSocket * ListenSocket, Socket * TheClientSocket)
{
boolean success = false;

if(TheSocket == null)
{
System.err.println("Null TheSocket passed in CRmiCommunicator.receiveAndUnmarshallInvoke().");
}
else
{
TheClientSocket = ListenSocket.accept();
}

return success;
}

Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo

Swinefeaster18-Nov-02 20:17

18-Nov-02 20:17

Thanks Joaquin. So in the code I posted, when the function returns, the new socket object created by ListenSocket.accept() will be deleted once the TheClientSocket local reference (?) variable goes out of scope, correct?

I guess then the only way to implement this would be to go "return TheClientSocket" instead of the boolean, and pass it back to the caller in that manner?

Thanks,

swine

Check out Aephid Photokeeper, the powerful digital
photo album solution at www.aephid.com.

Joaquín M López Muñoz18-Nov-02 20:52

Joaquín M López Muñoz

18-Nov-02 20:52

Thanks Joaquin. So in the code I posted, when the function returns, the new socket object created by ListenSocket.accept() will be deleted once the TheClientSocket local reference (?) variable goes out of scope, correct?

No, it'll be deleted when the garbage collector decides to sweep it off. Whether the socket itself, as a system resource, gets released, depends on the Finalize method of Socket (I think).

I guess then the only way to implement this would be to go "return TheClientSocket" instead of the boolean, and pass it back to the caller in that manner?

This is a way. Another is to have a wrapper class around Socket and pass this to the function:

class SocketWrapper
{
  SocketWrapper(Socket socket_)
  {
    socket=socket_;
  }
  public Socket socket;
}
...
public boolean receiveAndUnmarshallInvoke(CRmiInvokeMessage InvokeMessage,
ServerSocket ListenSocket, SocketWrapper TheClientSocket)
{
boolean success = false;

if(TheSocket == null)
{
System.err.println("Null TheSocket passed in CRmiCommunicator.receiveAndUnmarshallInvoke().");
}
else
{
TheClientSocket.socket = ListenSocket.accept();
}

return success;
}
...
Socket clientSocket;
receiveAndUnmarshallInvoke(...,new SocketWrapper(clientSocket));

Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo

Swinefeaster18-Nov-02 21:21

18-Nov-02 21:21

Lol that is really really weird. Are you sure it works that way? So I have to make a whole separate class just to pass a pointer back?

Also.... do I have to explicitly call Finalize() on Socket objects? I thought perhaps it all "just gets taken care of" with the garbage collector... No?

Much thanks,

swine

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Joaquín M López Muñoz18-Nov-02 21:59

Joaquín M López Muñoz

18-Nov-02 21:59

Lol that is really really weird. Are you sure it works that way? So I have to make a whole separate class just to pass a pointer back?

I'm sure. This is how things are in Java. The idiom seems a little strange at first, but Java programmers are used to it. C# provides references to handle this problem, I think (I'm no expert in either language).

Also.... do I have to explicitly call Finalize() on Socket objects? I thought perhaps it all "just gets taken care of" with the garbage collector... No?

You should never call Finalize yourself, this is done by the garbage collector. Java docs are not specific about this, but my hunch is that Socket.Finalize actually closes the socket (you might want to ask on some Java forum, they'll surely know).

Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo

S van Leent19-Nov-02 7:36

S van Leent

19-Nov-02 7:36

Finilize is used by java, at it's turn it calls the close method of a socket. It's done so, so an port is always closed when the class has no reference anymore,and is garbage collected. However, it's far better to use the close method yourself.

LPCTSTR Dutch = TEXT("Double Dutch Smile | :)

");

Swinefeaster18-Nov-02 21:58

18-Nov-02 21:58

ok i got it! check it out, a java implentation of a c++ pointer! Smile | :)

public class CPointer<br />
{<br />
  public CPointer()<br />
  {<br />
    m_TargetObject = null;<br />
  }<br />
<br />
  public CPointer(Object TargetObject)<br />
  {<br />
    m_TargetObject = TargetObject;<br />
  }<br />
<br />
  // Sets the pointer to null.<br />
  public void nullIt()<br />
  {<br />
    m_TargetObject = null;<br />
  }<br />
<br />
  // Returns true if the pointer is pointing to null.<br />
  public boolean isNull()<br />
  {<br />
    boolean isNullResult = false;<br />
<br />
    if(m_TargetObject == null)<br />
    {<br />
      isNullResult = true;<br />
    }<br />
<br />
    return isNullResult;<br />
  }<br />
<br />
  // Points the pointer at the given target object.<br />
  public void pointAt(Object TargetObject)<br />
  {<br />
    m_TargetObject = TargetObject;<br />
  }<br />
<br />
  // Returns the the object being pointed at.<br />
  public Object unwrap()<br />
  {<br />
    return m_TargetObject;<br />
  }<br />
<br />
  // The target object the pointer is pointing at.<br />
  private Object m_TargetObject;<br />
}<br />

so we just need to go:

  public boolean receiveAndUnmarshallInvoke(CRmiInvokeMessage InvokeMessage,<br />
   ServerSocket ListenSocket, CPointer ReturnedClientSocketPointer)<br />
  {<br />
    boolean success = false;<br />
<br />
    if(ListenSocket == null)<br />
    {<br />
      System.err.println("Null ListenSocket passed in CRmiCommunicator.receiveAndUnmarshallInvoke().");<br />
    }<br />
    else<br />
    {<br />
      try<br />
      {<br />
        Socket TheClientSocket = ListenSocket.accept();<br />
<br />
        // .....<br />
<br />
        ReturnedClientSocketPointer.pointAt(TheClientSocket);<br />
      }<br />
      catch (Exception e) <br />
      {<br />
        System.err.println("Socket failure (" + e.getLocalizedMessage()<br />
        + ") in CRmiCommunicator.receiveAndUnmarshallInvoke().");<br />
      }<br />
    }<br />
<br />
    return success;<br />
  }<br />
<br />

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Alexandru Savescu19-Nov-02 4:18

Alexandru Savescu

19-Nov-02 4:18

In Java everything is a reference. If you have two objects a and b and you
do:

a = b

then a references the same data as b, so modifying a will modify b as well. Frown | :(

Best regards,
Alexandru Savescu

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Alvaro Mendez19-Nov-02 5:25

Alvaro Mendez

19-Nov-02 5:25

In Java:

Definitions:

void PassInAConstantReference(final Object o)
{ }

void PassInAModifiableReference(Object o)
{ }

void PassInACopy(Object o)
{ }

Calls:

Object o = new SomeObject();
 
PassInAConstantReference(o);
 
PassInAModifiableReference(o);
 
PassInACopy(o.clone());

Regards,
Alvaro

Well done is better than well said. -- Benjamin Franklin
(I actually prefer medium-well.)

Swinefeaster19-Nov-02 14:29

a question about two CPU...

19-Nov-02 14:29

ahhh! thanks!

what about the c++ equivalent of:

<br />
boolean isEmpty(void)const;<br />

I don't think the following works in Java:

<br />
boolean isEmpty() final<br />
{<br />
}<br />

swine

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Mouse hover question

David Ensminger18-Nov-02 16:42

David Ensminger

18-Nov-02 16:42

How can I detect when the mouse cursor hovers over the system tray icon for my application? TrackMouseEvent() doesn't actually handle this since the application is a background process, since there's really no visible handle to give to it... Anyone know how to detect this?

Thanks!

liuty200618-Nov-02 16:27

liuty2006

18-Nov-02 16:27

I write a programe(with VC6).It run correctly at computer with ONE cpu(Win2000 server).But It can not run with TWO CPUs .
For my develop envirment is ONE cpu,so I can not locate the error correctly.

can you tell me the possible reason.
How can i locate the error?

thanks in advance.

liuty

Re: a question about two CPU...

Christian Graus18-Nov-02 16:59

Re: a question about two CPU...

18-Nov-02 16:59

Are you using threads ? I'd imagine that would be a likely error source, not being threadsafe.

Christian

No offense, but I don't really want to encourage the creation of another VB developer. - Larry Antram 22 Oct 2002

Hey, at least Logo had, at it's inception, a mechanical turtle. VB has always lacked even that... - Shog9 04-09-2002

Again, you can screw up a C/C++ program just as easily as a VB program. OK, maybe not as easily, but it's certainly doable. - Jamie Nordmeyer - 15-Nov-2002

liuty200618-Nov-02 17:57

liuty2006

18-Nov-02 17:57

yes!I use threads.
How to do with "being threadsafe".
what I would pay special attention to, when i write programe?

Re: a question about two CPU...

Christian Graus18-Nov-02 18:01