Re: Exception Semantics question

From:
"Bo Persson" <bop@gmb.dk>
Newsgroups:
microsoft.public.vc.mfc
Date:
Thu, 24 Jun 2010 18:22:48 +0200
Message-ID:
<88hf2oFeghU1@mid.individual.net>
RB wrote:

I have a question on try throw semantics. This has
nothing to do with whether I should try or catch but
just the fact that I don't understand what is going
on here. Admittedly this is not any real code but a
scenario that I happened on by accident in experimenting
with writing my own exception class. The below code
compiles and runs with no errors but a newb like me
doesn't understand how. See comment on GlobalFunc

#include <iostream.h>

class ClassNoObject
{
public:
ClassNoObject(){}
~ClassNoObject(){}
void ClsNoObjFunc()
 {
  cout << "no object class printing? \n";
 }
};

void GlobalFunc()
{ // How can throw construct a class definition with
  // no object, but seemingly does in the debugger ?
 // What is happening here ?

 cout << "fixing to throw ClassDefinition? \n";
 throw ClassNoObject();


This is the construction of a new object, which is then thrown. There
is now 'new' here, so it is not a pointer.

}

void main(void)
{
try
 {
  GlobalFunc();
 }

// The E instead of * E appears it is passing a copy,
// but a copy of what object ?

catch( ClassNoObject E )
 {
  E.ClsNoObjFunc();
  cout << "Caught exception\n";
 }
}


Right, you catch the exception object by value. Quite ok.

Bo Persson

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