在类的函数中使用'const' [英] Using 'const' in class's functions

问题描述

我已经看到了很多const关键字在函数中的使用，所以我想知道它是什么。我在这里读了smth： http://duramecho.com/ComputerInformation/WhyHowCppConst.html 。

I've seen a lot of uses of the const keyword put after functions in classes, so i wanted to know what was it about. I read up smth at here: http://duramecho.com/ComputerInformation/WhyHowCppConst.html .

它表示使用const，因为函数可以尝试更改对象中的任何成员变量。如果这是真的，那么它应该被无处不在地使用，因为我不希望任何成员变量以任何方式被改变或改变。

It says that const is used because the function "can attempt to alter any member variables in the object" . If this is true, then should it be used everywhere, because i don't want ANY of the member variables to be altered or changed in any way.

class Class2
{ void Method1() const;
  int MemberVariable1;} 

那么，const的真正定义和用法是什么？ / p>

So, what is the real definition and use of const ?

推荐答案

const方法可以在const对象上调用：

A const method can be called on a const object:

class CL2
{
public:
    void const_method() const;
    void method();

private:
    int x;
};


const CL2 co;
CL2 o;

co.const_method();  // legal
co.method();        // illegal, can't call regular method on const object
o.const_method();   // legal, can call const method on a regulard object
o.method();         // legal

此外，它还告诉编译器const方法不应该改变状态对象并将捕获这些问题：

Furthermore, it also tells the compiler that the const method should not be changing the state of the object and will catch those problems:

void CL2::const_method() const
{
    x = 3;   // illegal, can't modify a member in a const object
}

通过使用mutable修饰符，上述规则的一个例外，但你应该先获得良好的const正确性，在你冒险进入该领土。

There is an exception to the above rule by using the mutable modifier, but you should first get good at const correctness before you venture into that territory.

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