CODEWITHSUNDEEP
c++templatespointer-to-member
Zerreth
Zerreth

Reputation: 145

Template Member Function Pointers

I currently have a problem, VS2010 nags that "TFunctionPointer" used in the constructor of "Nuke" & as datamember is undefined. Could someone please explain to me why this is ? Any help is very much appreciated.

template<typename T>
typedef void (T::* TFunctionPointer)();

class Nuke
{
public:
    Nuke( TFunctionPointer pFunction );
    virtual ~Nuke();

private:
    TFunctionPointer m_pFunction;

};

// EDIT

What I'm trying to do is allow a function pointer to any type of class to be stored and called on destruction of the Nuke object. A twist on RAII. But I guess it isn't possible. Thanks for the help guys.

// EDIT

Apparently Boost::shared_ptr is what I was looking for.

Upvotes: 0

Views: 5652

Answers (2)

Grizzly
Grizzly

Reputation: 20211

C++ doesn't support template typedefs, so template<typename T> typedef is illegal.

If you can use C++11 you might be able to use template aliases. I'm not quite sure if that is possible with memberfunction pointers and can't guarantee the syntax is correct, but I would expect it to be something like the following:

template <typename T>
using TFunctionPointer = void(T::*)();

Of course VS2010 probably doesn't support that anyways.

Anyways your Nuke class doesn't give a type for the TFunctionPointer, so even if that typedef where legal, you are trying to pass a template instead of a concrete type, which isn't possible.

You could wrap your function pointer into a type and use a properinstantiation: 

template<typename T> struct FunctionPointer { typedef void (T::*Type)(); };
class Nuke {
public:
    Nuke(FunctionPointer<Nuke>::Type pFunction);
    virtual ~Nuke();
private:
    FunctionPointer<Nuke>::Type m_pFunction;

};

Upvotes: 1

Stuart Golodetz
Stuart Golodetz

Reputation: 20656

Template typedefs aren't legal in C++.

What you can do though (in both "old" and "new" C++) is this:

template <typename T>
struct TFunctionPointer
{
    typedef void (T::*Type)();
};

class Nuke
{
public:
    Nuke( TFunctionPointer<Nuke>::Type pFunction );
    virtual ~Nuke();

private:
    TFunctionPointer<Nuke>::Type m_pFunction;
};

Upvotes: 4

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