Re: Exception Propagation / Copy Constructors

Hello All,

Please consider the following:

#include <iostream>

using namespace std;

class Foo
{
   public:
      Foo()
      {
         cout << "Foo::Foo()" << endl;
      }

      ~Foo()
      {
         cout << "Foo::~Foo()" << endl;
      }

      Foo(const Foo &)
      {
         cout << "Foo::Foo(const Foo &)" << endl;
      }

};

void func3()
{
   throw Foo();

}

void func2()
{
   func3();

}

void func1()
{
   func2();

}

int main()
{
   try
   {
      func1();
   }
   catch(const Foo &)
   {
      cout << "Caught Foo" << endl;
   }

}

This results in the following output:

Foo::Foo()
Caught Foo
Foo::~Foo()

This shows that the copy constructor does not run. Yet, if I make the
copy constructor private, the compiler balks with the following:

main.cpp: In function `void func3()':
main.cpp:20: error: `Foo::Foo(const Foo&)' is private
main.cpp:27: error: within this context
main.cpp:20: error: `Foo::Foo(const Foo&)' is private
main.cpp:27: error: within this context

This leads to two questions:

1. Why does the compiler balk about inaccessibility of a function (the
copy constructor) it does not use?

2. Why *is* it not using the copy constructor? I would have expected
to see the exception object copy constructed / destructed at each
level of the call stack as that stack is unwound.

Thanks,
Dave