类变量：公共访问只读，但私有访问读/写 [英] Class variables: public access read-only, but private access read/write

问题描述

Whoopee，暂时不在那个套接字库上工作。我试图在C ++中教育自己一点点。

Whoopee, not working on that socket library for the moment. I'm trying to educate myself a little more in C++.

有了一个方法，使一个变量只读的公共，但读+写当私人访问？例如像这样：

With classes, is there a way to make a variable read-only to the public, but read+write when accessed privately? e.g. something like this:

class myClass {
    private:
    int x; // this could be any type, hypothetically

    public:
    void f() {
        x = 10; // this is OK
    }
}

int main() {
    myClass temp;

    // I want this, but with private: it's not allowed
    cout << temp.x << endl;


    // this is what I want:

    // this to be allowed
    temp.f(); // this sets x...

    // this to be allowed
    int myint = temp.x;

    // this NOT to be allowed
    temp.x = myint;
}

我的问题，精简是如何允许完全访问<$ c $从 f（）内，但是从任何其他地方只读访问，即 int newint = temp.x ; 允许，但 temp.x = 5; 不允许？像一个常量变量，但可写从 f（） ...

My question, condensed, is how to allow full access to x from within f() but read-only access from anywhere else, i.e. int newint = temp.x; allowed, but temp.x = 5; not allowed? like a const variable, but writable from f()...

编辑：我忘了提及计划返回一个大的向量实例，使用一个getX（）函数只会做一个副本，它不是真正的最佳。我可以返回一个指针，但这是坏的做法iirc。

I forgot to mention that I plan to be returning a large vector instance, using a getX() function would only make a copy of that and it isn't really optimal. I could return a pointer to it, but that's bad practice iirc.

PS：如果我只想基本上显示我的知识的指针，完成还是不完成？谢谢！

P.S.: Where would I post if I just want to basically show my knowledge of pointers and ask if it's complete or not? Thanks!

推荐答案

当然可以：

class MyClass
{
    int x_;

public:
    int x() const { return x_; }
};

如果你不想复制一个（对于整数，没有开销）如下：

If you don't want to make a copy (for integers, there is no overhead), do the following:

class MyClass
{
    std::vector<double> x_;

public:
    const std::vector<double>& x() const { return x_; }
};

这不会产生任何副本。它返回 对const 的引用

This does not make any copy. It returns a reference to const.

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