C++ Template Question

[Steven Green]

Hi Guys, I've been away from C++ since 2001 (been playing in Java land) but
I am trying to refresh my grey cells with C++.
What I am trying to do is wrap a std::list<T*> with a simple wrapper.

template <class T>
class Adapter
{
private:
std::list<T*> data;
public:
void remove(T*);
}

void Adapter<T>::remove(T *d)
{
std::list<T*>::iterator i = data.begin(); //the offencive line
}

Pardon me if there are any syntax errors in the above code, I am typing this
not cut and pasting.

The problem:
In th above code I create an iterator of type T*. This doesn't work it wants
the T* to be a class type:
For example:
std::list<Widget>::iterator i = data.begin(); //works
std::list<T*>::iterator i = data.begin(); //does not work.

I don't doubt that I am doing something dumb, but I cannot find my C++ book
(it is neatly tucked away under a pile somewhere to be sure)
Any thoughts on this would be appreciated.
Thanks,
Steve

 

[mlimber]

Hi Guys, I've been away from C++ since 2001 (been playing in Java land) but
I am trying to refresh my grey cells with C++.
What I am trying to do is wrap a std::list<T*> with a simple wrapper.

template <class T>
class Adapter
{
private:
std::list<T*> data;
public:
void remove(T*);
}

Could your problem be that you are missing this line:

void Adapter<T>::remove(T *d)
{
std::list<T*>::iterator i = data.begin(); //the offencive line
}

Pardon me if there are any syntax errors in the above code, I am typing this
not cut and pasting.

The problem:
In th above code I create an iterator of type T*. This doesn't work it wants
the T* to be a class type:
For example:
std::list<Widget>::iterator i = data.begin(); //works
std::list<T*>::iterator i = data.begin(); //does not work.

I don't doubt that I am doing something dumb, but I cannot find my C++ book
(it is neatly tucked away under a pile somewhere to be sure)
Any thoughts on this would be appreciated.
Thanks,
Steve

If that's not it, please cut and paste a complete but minimal sample
that demonstrates the problem.

Cheers! --M

 

[Bob Hairgrove]

Hi Guys, I've been away from C++ since 2001 (been playing in Java land) but
I am trying to refresh my grey cells with C++.
What I am trying to do is wrap a std::list<T*> with a simple wrapper.

template <class T>
class Adapter
{
private:
std::list<T*> data;
public:
void remove(T*);
}

void Adapter<T>::remove(T *d)
{
std::list<T*>::iterator i = data.begin(); //the offencive line
}

Pardon me if there are any syntax errors in the above code, I am typing this
not cut and pasting.

The problem:
In th above code I create an iterator of type T*. This doesn't work it wants
the T* to be a class type:
For example:
std::list<Widget>::iterator i = data.begin(); //works
std::list<T*>::iterator i = data.begin(); //does not work.

I don't doubt that I am doing something dumb, but I cannot find my C++ book
(it is neatly tucked away under a pile somewhere to be sure)
Any thoughts on this would be appreciated.
Thanks,
Steve

Try this:

void Adapter<T>::remove(T *d)
{
typename std::list<T*>::iterator i = data.begin();
// ^^^^^^^^
}

You need the keyword "typename" because the iterator's type depends on
the template parameter. If you specify a real type such as Widget, the
compiler can resolve it without the typename.

Implicit typename has been deprecated for 2 or 3 years now, so maybe
it used to work in 2001.

 

[Greg]

Hi Guys, I've been away from C++ since 2001 (been playing in Java land) but
I am trying to refresh my grey cells with C++.
What I am trying to do is wrap a std::list<T*> with a simple wrapper.

template <class T>
class Adapter
{
private:
std::list<T*> data;
public:
void remove(T*);
}

void Adapter<T>::remove(T *d)
{
std::list<T*>::iterator i = data.begin(); //the offencive line
}

Pardon me if there are any syntax errors in the above code, I am typing this
not cut and pasting.

The problem:
In th above code I create an iterator of type T*. This doesn't work it wants
the T* to be a class type:
For example:
std::list<Widget>::iterator i = data.begin(); //works
std::list<T*>::iterator i = data.begin(); //does not work.

I don't doubt that I am doing something dumb, but I cannot find my C++ book
(it is neatly tucked away under a pile somewhere to be sure)
Any thoughts on this would be appreciated.

Try:

typename std::list<T*>::iterator i = data.begin();

Greg

 

[John Carson]

Try this:

void Adapter<T>::remove(T *d)
{
typename std::list<T*>::iterator i = data.begin();
// ^^^^^^^^
}

Even better, try this:

template<class T>
void Adapter<T>::remove(T *d)
{
typename std::list<T*>::iterator i = data.begin();
// ^^^^^^^^
}