How to write a function pointer as template?
template <typename T>
T (*PtrToFunction)(T a);
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3That would amount to a "template typedef", which doesn't exist. In C++11 you have template aliases, but I'm not sure if they cover that situation.Kerrek SB– Kerrek SB2011-09-03 14:19:57 +00:00Commented Sep 3, 2011 at 14:19
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1If your application's size warrants it, use a more general functor object like Boost.Function which allows you to use any kind of callable object, not just function pointers. If you're writing a small app, don't bother.Paul Manta– Paul Manta2011-09-03 14:36:26 +00:00Commented Sep 3, 2011 at 14:36
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4 Answers
I am assuming you are trying to declare a type (you cannot declare a "template variable" without a concrete type).
C++03 doesn't have template typedefs, you need to use a struct as a workaround:
template <typename T>
struct FuncPtr {
typedef T (*Type)(T a);
};
...
// Use template directly
FuncPtr<int>::Type intf;
// Hide behind a typedef
typedef FuncPtr<double>::Type DoubleFn;
DoubleFn doublef;
C++11 template aliases will eliminate the struct workaround, but presently no compilers except Clang actually implement this.
template <typename T>
typedef T (*FuncPtr)(T a);
// Use template directly
FuncPtr<int> intf;
// Hide behind a typedef
typedef FuncPtr<double> DoubleFn;
DoubleFn doublef;
1 Comment
Christopher Smith
Just updating this old entry to mention that as of GCC 4.7, GCC now supports template aliases.
If you mean create a type for that function, you could do something like this:
template<typename T>
struct Function {
typedef T (*Ptr)(T);
};
Then use it like
int blah(Function<int>::Ptr a) { }
Comments
You can not do that. You can only create function pointers with concrete type.
Comments
It's ok on Visual Studio 2015 and on GCC you should use command line option -std=c++11
template<class T> using fpMember = void (T::*)();
