关于课程中的方法 [英] About the method in the class

问题描述

虚拟方法的地址存储在类的vir_table中，当我们调用虚拟方法时，我们可以在类中搜索vir_table以获得所需的方法，但是普通方法未存储在vir_table中.因此，当我们通过对象或指针调用普通方法时，如何知道普通方法的地址?

The address of virtual method is stored in the vir_table in class.When we call a virtual method, we can search the vir_table in class to get that the method which we wanted.But the normal method is not stored in the vir_table.So, when we call a normal method by an object or a pointer.How do it know the normal method address?

推荐答案

非虚拟方法就像在这方面，常规的全局函数除外，只是它接受额外隐藏的此指针作为其第一个参数.非虚拟方法的地址是过程地址空间中的固定位置.

这可能是一个愚蠢的示例，但是以下代码:

A non-virtual method is just like a normal global function in this regard except that it accepts an extra hidden this pointer as its first parameter. The address of a non-virtual method is a fix location in your process address space.

This may be a stupid example but the following code:

struct S
{
    int i;
    void f()
    {
        printf("%d\n", i);
    }
}

S s;
s.f();

...基本上被编译成如下形式:

...is basically compiled to something like this:

struct S
{
    int i;
}

void f(S* _this_)
{
    printf("%d\n", _this_->i);
}

S s;
f(&s);

知道这一点后，您发出s.f()方法调用就不会发生魔术.通过将S实例指定为其第一个隐藏参数(在本例中为&s)，您只需调用S命名空间中的f()函数"即可.

唯一的不同是，第一块代码的可读性趋于提高(我认为，尤其是当代码库的大小增加时)，并且可以通过将方法f()设为私有和可以看到S的私有成员(这是某种文档，可以防止滥用-将人类编码人员的错误转换为编译错误)，对于第二个代码块(类似于C代码)来说，情况并非如此.我通常会通过关于非虚拟方法的类似示例，开始为C程序员解释C ++的美丽. :-)

Knowing this reveals that there is no magic happening when you issue an s.f() method call. You just call the f() "function" residing in the S namespace by specifying an S instance as its first hidden parameter (that is &s in our case).

The only difference is that the readability of the code in the first block tends to be better (in my opinion - especially when the size of codebase increases) and there you can hide method f() from outer world by making it private and f() can see the private members of S (this is some kind of documentation and prevention of abuse - converting human coder mistakes into compile errors), the same isn''t true for the second code block that is much like C code. I usually start to explain the beauty of C++ for C coders through a similar example on non-virtual methods. :-)

在程序编译期间会分配常规方法地址

the normal method address gets assigned during the program compilation

float (SomeClass::*my_memfunc_ptr)(int, char *);
// For const member functions, it's declared like this:
float (SomeClass::*my_const_memfunc_ptr)(int, char *) const;

   my_memfunc_ptr = &SomeClass::some_member_func;
 // This is the syntax for operators:
 my_memfunc_ptr = &SomeClass::operator !;

成员函数指针和最快的C ++代理 [ ^ ]

Member Function Pointers and the Fastest Possible C++ Delegates[^]

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