Problem with multiple inheritance

[Loreno Oliveira]

Hi there,

besides I always check this forum about my doutbs this is my first post here. In fact, this problem is boring me for a day and could not find an answer yet :-(

The scenario is illustrated bellow with code snipets:

//MStreamError.h
 
class MStreamError {
private:
    char* mesg;
 
public:
 
    explicit MStreamError( const char* msg ) {
        //impl...
    }
 
    ~MStreamError() {
        //impl...
    }
 
    void report() const {
        //impl...
    }
 
    const char* get_message() {
        //impl...
    }
};
 
//ServerRuntimeErrors.h
 
class ServerRuntimeErrors : public virtual MStreamError {
public:
    ServerRuntimeErrors( const char* errorMessage ) : MStreamError( errorMessage ) {}
};
 
//ClientRuntimeErrors.h
 
class ClientRuntimeErrors : public virtual MStreamError {
public:
    ClientRuntimeErrors( const char* errorMessage ) : MStreamError( errorMessage ) {}
};
 
//InterfaceInicializationError.h
 
class InterfaceInitializationError : public ServerRuntimeErrors, public ClientRuntimeErrors {
public:
 
    InterfaceInitializationError( const char* msg ) {};
};
 

Well, my doubt is how to initialize InterfaceInitializationError since it inherits from both ClientRuntimeErrors and ServerRuntimeErrors. In fact, after following the compiler error messages, I tried putting " : MStreamError( msg ), ServerRuntimeErrors( msg ), ClientRuntimeErrors( msg )" just after the InterfaceInitializationError ctor, and it worked. However, I do not know is this solution (using virtual inheritance and this order of constructors) is correct, or even what is happening here...

I will be thankfull is someone could give me some hint about that or point me out some reference where I could understand this situation...

Regards!!

[weaknessforcats]

With multiple inheritance there are new compiler rules for calling base class
constructors:

THE COMPILER WON' T CALL THEM.

That means in a multiple inheritance constructor, you have explicitly call all of the base class contructors yourself. That includes ALL indirect base class coinstructors as well. Like this:

InterfaceInitializationError::InterfaceInitializat ionError( const char* msg )
: ServerRuntimeErrors(msg), ClientRuntimeErrors(msg)
{};

This is different from single inheritance where you are not allowed to call indirect base class constructors but only the the immediate base class constructor.

[weaknessforcats]

Oh, I forgot:

Check out C++ Primer Plus Stephane Prata 5th Ed. Read section on "New Constructor Rules"