Question

I have some complex template code where the copy-constructor of OPC is being called even though I am only creating a reference to OPC (the actual instance is OP_S, which as a child class of OPC, should not result in a copy-construction call).

I am using gcc 4.6.1

The code is below.

#include <stdio.h>

class OPC
{
    public:
        OPC() { }
        OPC( const OPC& f ) {
            fprintf( stderr, "CC called!!!\n" );
        }
};

template<class T>
class SL : public T
{ };

template<class T>
class S : public SL<T>
{ };

class OP_S : public S<OPC>
{ };

class TaskFoo
{
    public:
        TaskFoo( OPC& tf ) :
            m_opc(  tf ),
            m_copc( tf )
        { }
        OPC& getOPC() { return m_opc; }

    private:
        OPC&       m_opc;
        const OPC& m_copc;
};

int main(int argc, char** argv)
{
    OP_S op_s;
    TaskFoo tf( op_s );

    auto opc = tf.getOPC();  // this line results in a call to OPC's CC

    return 0;
}

Answer as noted by James McNellis below – need auto& instead of auto.

Answer 1

auto opc declares an object, not a reference. It is the same as if you had said OPC opc.

If you want opc to be a reference, you need auto& opc.