C ++ typedef成员函数签名语法 [英] C++ typedef member function signature syntax

问题描述

我想声明一个成员函数签名的类型定义。全局函数typedef如下：

  typedef int（function_signature）（int，int） 
 typedef int（* function_pointer）（int，int）; 
  

但是我不能为成员函数做同样的事情：

  typedef int（foo :: memberf_signature）（int，int）; // memberf_pointer不是foo 
的成员typedef int（foo :: * memberf_pointer）（int，int）; 
  

这听起来像是逻辑上的，因为foo ::ist语法访问类foo。
我如何只是签名typedef

解决方案

对于有关尴尬函数指针语法的问题，我个人使用cheat-sheet：函数指针教程（ 可在此下载，感谢向量以指出它）。

然而，成员函数的签名有点不同于

你可能知道，一个成员函数有一个隐藏的参数 this

  typedef int（Foo :: * Member）（int，int） 
  

可以指定传递给函数的第一个元素是 Foo * （因此你的方法真的需要3个参数，当你想到它，而不只是2。

，用于强制您指定类型。

函数指针可能指的是一个虚函数，在这种情况下事情可能会变得相当复杂，因此，事实上，在Visual Studio中，函数指针的大小可能在常规指针大小的1和4倍之间变化，这取决于函数是否是函数的大小virtual，特别是。

因此，函数引用的类是签名的一部分，并且没有解决方法。 p>

I want to declare type definition for a member function signature. Global function typedefs look like this:

typedef int (function_signature)(int, int);
typedef int (*function_pointer) (int, int);

But I'm not able to the same thing for a member function:

typedef int (foo::memberf_signature)(int, int);   // memberf_pointer is not a member of foo
typedef int (foo::*memberf_pointer)(int, int);

It sounds logically to me, because "foo::" ist the syntax to access a member in the class foo. How can I typedef just the signature?

解决方案

For questions regarding the awkward function pointer syntax, I personally use a cheat-sheet: The Function Pointers Tutorial (downloadable here, thanks to Vector for pointing it out).

The signature of a member function, however, is a bit different from the signature of a regular function, as you experienced.

As you probably know, a member function has a hidden parameter, this, whose type need be specified.

typedef int (Foo::*Member)(int, int);

does let you specify that the first element passed to the function will be a Foo* (and thus your method really takes 3 arguments, when you think of it, not just 2.

However there is another reason too, for forcing you to specify the type.

A function pointer might refer to a virtual function, in which case things can get quite complicated. Therefore, the very size of the in-memory representation changes depending on the type of function. Indeed, on Visual Studio, a function pointer's size might vary between 1 and 4 times the size of a regular pointer. This depends on whether the function is virtual, notably.

Therefore, the class the function refers to is part of the signature, and there is no work-around.

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