如何声明一个指向返回类型X和输入参数A的函数的指针？

Question

What is the general form of declaring a pointer to a function which, say is of return type X and accepts the input parameter &Y?

is it:

X my_function(Y &y){
    //code
}

X (*my_pointer) (Y &y) = my_function;

?

Answer 1

X (*fptr)(Y&) = my_function;

Or:

auto fptr = my_function; // c++11

Or:

std::function<X(Y&)> fptr(my_function); // c++11, boost::function if not

Answer 2

What you wrote is OK, but you normally do not write the name of function arguments if you just want to declare a function pointer of that type:

X (*my_pointer) (Y&) = my_function;

Depending on your taste, you may want to be more C++11-ish and write:

#include <type_traits>

std::add_pointer<X(Y&)>::type my_pointer = my_function;

It can get even more readable with a template alias:

#include <type_traits>

template<typename T>
using AddPointer = typename std::add_pointer<T>::type;

AddPointer<X(Y&)> my_pointer = my_function;

Or even use auto and forget about naming the function type explicitly, as suggested by hmjd in his answer . If you would later need to retrieve the type, you could do:

decltype(my_pointer)

Answer 3

• is it:

   X my_function(Y &y){ //code } X (*my_pointer) (Y &y) = my_function; 

  ?

Yes