mirror of
https://github.com/Light-City/CPlusPlusThings.git
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dfe1c933b3
- const README: rewrite the space-saving claim per issue #5 follow-ups (constant-expression const vs #define immediates; which const qualify as constant expressions) - const README: fix the class-section diagnosis per issue #338 (overload resolution picks the const overload; the restriction only surfaces once that overload is removed) - sizeof README: virtual-inheritance result is compiler-dependent (GCC merges vbptr+vfptr -> 16, MSVC keeps them separate -> 32) #246 - static README: new section on internal linkage / access restriction with anonymous-namespace comparison #142 - 10-day practice: full problem list table + fixed day links #136 - new design_pattern/singleton/singleton_default.hpp: reusable thread-safe CRTP singleton template, compile+concurrency tested #303
78 lines
2.0 KiB
Markdown
78 lines
2.0 KiB
Markdown
> 来自 [C++那些事网站](https://light-city.github.io/stories_things/cpp-things/cpp-dereference-operator/) 的文章，由站点同步脚本导出。
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# C++ 解引用运算符 *
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## 0.导语
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通常我们在操作指针时，会使用到`*`，例如：
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```cpp
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int a = 1;
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int *ptr = a;
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std::cout << *ptr << std::endl;
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```
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除此之外，还有什么用途？
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答案是肯定的，例如，在C++中还有下面三类：
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- `::*`
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- `.*`
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- `->*`
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那么你知道这三个分别表示什么吗？
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## 1.::*
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`::*`被称之为**Pointer to member declarator**，指向成员声明符的指针。
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举个例子吧：
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下面这个例子你如何区w_的地址呢？
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如果你写成`double * d = &w_`; 它便是无效的，因为不知道`w_`在哪里哦，所以需要指向成员声明符的指针，这样便可以进行绑定，有了这个指针之后，便可以访问成员了，继续讲后面两个。
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```cpp
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class Rectangle {
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public:
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double w_, h_;
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Rectangle(double w, double h) : w_(w), h_(h) {}
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double area() { return w_ * h_; }
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};
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int main() {
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Rectangle r{2.1, 3.2};
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double Rectangle::* w = &Rectangle::w_;
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r.*w = 2.2;
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std::cout << r.w_ << std::endl;
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};
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```
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## 2..*
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`.*`被称为pointer to member of object，这个比较好理解，就是访问**对象**成员的指针，指向成员的指针允许你引用类对象的非静态成员。不能使用指向成员的指针指向静态类成员，因为静态成员的地址与任何特定对象都没有关联。
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所以看上面的例子中有了这一行代码，修改成员w的值为2.2。
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```cpp
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r.*w = 2.2;
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```
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## 3.->*
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`->*`被称为pointer to member of pointer，这个就更好理解了，跟.*类似，不过操作的是**指针对象**成员的地址，
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所以对应的例子变为：
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```cpp
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Rectangle r{2.1, 3.2}, *pr;
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pr = &r;
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std::cout << pr->*w << std::endl;
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```
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更加详细的请阅读cppreference.com。
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> https://en.cppreference.com/w/cpp/language/pointer#Pointers_to_members
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你学会了吗？本节完~ |