Question

I hae written the following code:

class Object
{
   public:
   Object()
   {}
};

template <class T>
class Reg : public Object
{
    T val,val_new;
    public:
    Reg(T initval)
    {
    super( );
    val=initval;
    } 
};

The error in the code is

t.cpp: In constructor 'Reg<T>::Reg(T)':
Line 15: error: there are no arguments to 'super' that depend on a template parameter,
so a declaration of 'super' must be available
compilation terminated due to -Wfatal-errors.

How can i eliminate the error?

Answer 1

class Object
{
public:
   Object() {}
};

template <class T>
class Reg : public Object
{
    T val,val_new;
public:
    Reg(T const& initval)
        : val( initval )
    {} 
};

There is no super in standard C++. Some compilers offer it as a language extension, but in standard C++ if you want a generic name for “the” base class, then you have to typedef it. For example, in class Reg you can typedef Object Base;.

The construction : val( initval ) is a constructor initializer list, where essentially you call constructors of members and base classes, avoiding default construction.

Finally, the const&, passing by reference, avoids time-consuming and memory-consuming copying of the actual argument; it’s another thing that’s different in C++ (compared to Java, which I’m assuming that you’re coming from).