inherit constructor

[rmxhaha]

I've searched google and looks around and found that it's possible to inherit a constructor from base class. But I simply don't know the syntax. I think the pattern is something like this code bellow.

class B {
public:
	B(){
	}
private:
	int haha;
};

class I : public B {
	using B::B;
};

but this code produce error in my compiler

error: 'B:B' name constructor

FYI, My compiler is codeblocks 10.05 no patch to the gcc and using C++0x

So what's the correct syntax to inherit class constructor ?

[Catfish3]

Maybe you think about calling the base constructor:

class B {
public:
	B(){
	}
private:
	int haha;
};

class I : public B {
public:
	I(): B() {
	}
};

[LB]

http://stackoverflow.com/questions/4417797/why-is-inheriting-constructors-not-supported-by-all-of-the-existing-c-compiler

The compiler you're using is likely not to have full support yet. In fact I do not know of any compiler will full 100% C++11 support yet.

[rmxhaha]

I think that solves the problem but if there is a parameter in the constructor
Hmmm something like this

class B{
public:
    B( int a, int b, int c ){ 
           d = a; 
           e = b;
           f = c;
    }
private:
    int d,e,f;
}

class I {
    I( int a, int b, int c ) : B( a,b,c ) {} 
}

is there better ways to do this ?
because if the base class constructor parameter change then all the derived class inheriting the class consturctor this way must change and it's an extra work in every work.

[Cubbi]

You could just forward everything

class B{
public:
    B( int a, int b, int c )
    : d(a), e(b), f(c) { }
private:
    int d,e,f;
};

class I : public B {
public:
    template<typename ...A>
    I(A&& ...a)
    : B(std::forward<A>(a)...) {}
};

[JLBorges]

g++ - Delegating constructors GCC 4.7, Inheriting constructors GCC 4.8
http://gcc.gnu.org/projects/cxx0x.html

clang - Delegating constructors Clang 3.0, Inheriting constructors Not implemented
http://clang.llvm.org/cxx_status.html

[rmxhaha]

What's with the C++11...
Doesn't this inheriting consturctor exist before C++0x ?
and yes my compiler is capable of doing it...
So don't mind the version

class I : public B {
public:
	I(): B() {
	}
};

the code above can run without problem

I just need the solution for inheriting the consturctor without knowing the parameter to the consturctor

and I don't know about std::forward. Never heard of it and have to search about it...

is the forward version like this ?

class I : public B {
public:
    template<typename X, typename Y, typename Z>
    I(X&& a, Y&& b, Z&& c)
    : B(std::forward<X>(a),std::forward<Y>(b),std::forward<Z>(c)) {}
};

templating and inheriting is the things I don't want to combine. They produces obsecure error message if there is one and I hate it but somehow have to deal with it.

[JLBorges]

> Doesn't this inheriting consturctor exist before C++0x ?

http://www.stroustrup.com/C++11FAQ.html#inheriting


> templating and inheriting is the things I don't want to combine.
> They produces obsecure error message if there is one

They can also cause unexpected or unintuitive behaviour unless one is careful.

struct B
{
    B( int a, int b, int c ) : d(a), e(b), f(c) {}
    private: int d,e,f;
};

struct I : B
{
    template< typename... A >
        I( A&& ...a ) : B(std::forward<A>(a)...) {}

    I( double a, int b, char c ) : B( int( std::ceil(a) + 0.1 ), b, c ) {}
    I( const std::string& n, int a, int b, int c ) : B(a,b,c), name(n) {}

    const std::string name = "anonymous" ;
};

int main()
{
    I a( 2.6f, 1, 2 ) ; // un-intuitive

    I b( std::string("a name"), 1, 2, 3 ) ; // *** error
}

[rmxhaha]

Thanks for the helps...
I am sorry, I am not too well informed...

This part give error message

    template< typename... A >
        I( A&& ...a ) : B(std::forward<A>(a)...) {}

Maybe my compiler is just not new enough

Maybe copy paste produces less stress for my brain than inheriting.