Compilation error - no matching function for call to 'Exception::Exception(Exception)'

Question

Hello. I can not solve this problem for a while. I would be glad for some advice.

When I try to throw an exception (self created one in Java style)

throw Exception ();

compiler make a protest:

DataTypes/Date.cpp:24: error: no matching function for call to `Exception::Exception(Exception)' DataTypes/Date.cpp:24: error: in thrown expression

It does not work with any of the constructors I have. What is the problem? Here is header file of the Exception:

class Exception
{

public:
 Exception(void);
    explicit Exception(const char *);
    explicit Exception(const Exception &);
    Exception(const char *, const Exception &);
 virtual ~Exception();

 const char * message;
 const Exception & cause;

};

I should mention that when I leave just implicit constructor and the second one it works.

Thank you for any help.

Answer 1

Your copy constructor is marked explicit, which means it isn't really a copy constructor. Thrown objects must be copyable.

To elaborate:

The explicit keyword means that a single-argument constructor cannot be used to implicitly convert a variable of the argument type to an object of the constructed type. You have to do it explicitly with the class name. For example, your constructor from const char* is explicit, so the compiler will never implicitly convert a const char* to a new object of type Exception, without you writing out Exception("some string here"). On the other hand, you do want the compiler to be able to implicitly make one Exception object into another Exception object (that's what a copy constructor does!), so by taking the constructor that would otherwise be the copy constructor and marking it with the explicit keyword, you have completely eliminated its ability to make copies.

Answer 2

By throw Exception(); you create a local instance of the exception class, which is then copied off the stack. Remove explicit from the copy-constructor.

Edit:

If your copy constructor doesn't do anything - just omit it. The compiler will generate one for you.