指针和参考 [英] pointers and references

问题描述

我是c ++的新手.我无法理解的一件事. *或&是什么类方法名称之前是什么意思?我也通过简单的功能看到了它.例如，这里的类方法返回this指针，但是什么是&"为了?如果此类方法更改了对象，那么const又是什么呢?

Hi, i''m new at c++. There is one thing I can''t understand. What do * or & before class method name mean? Also I have seen it after simple functions. For example, here class method returns the this pointer, but what is "&" for? Also what is const for if this class method changes object?

const Counter& Counter::operator++()
   {
       ++itsVal;
       return *this;
    }

推荐答案

在方法名之前不是"*"或&"，而是"'*'或'&键入后.

例如:

It isn''t a ''*'' or an ''&'' before a method name, it''s a ''*'' or an ''& after a type.

For example:

int * fun(int p)
   {
   }

是说名为"fun"的函数返回一个指向整数的指针. *是指int而不是fun. &"也是如此:它将返回对整数的引用.

在您给出的示例中，class方法不会返回this指针"-它返回对项目this所指向的点的引用(该类的实例)-参见this之前的"*"吗?

Is saying that the function called "fun" returns a pointer to an integer. The ''*'' refers to the int not the fun. The same applies for ''&'': it would return a reference to an integer.

In the example you give, teh class method does not "return the this pointer" - it returns a reference to the item this points at (the instance of the class) - see the ''*'' before this?

这不只是在类之前"，而是这是运算符"++"的返回类型的规范的一部分.
您具有类型SomeType，符号SomeType&表示另一种类型，对类型SomeType的实例的引用"，并且consts使常量修改的变体成为同一类型，即符号const SomeType&表示对SomeType类型的实例的引用；该实例无法通过该引用进行修改".

这种const修改可以被认为是语法糖，并且是一种愚蠢的功能，可以保护类型的变量免受实例的修改，但是变量本身的值可以修改，因为您以后可以为它分配相同类型的其他引用.

C ++引用在这里得到了很好的解释，包括它们的语义和用法:
http://en.wikipedia.org/wiki/Reference_%28C%2B%2B%29 [^ ].

—SA

This is not just "before class", rather, this is the part of the specification of the return type of the operator "++".

You you have a type SomeType, the notation SomeType& means another type, "a reference to the instance of the type SomeType", and the consts makes the constant-modified variant the the same type, that is, the notation const SomeType& means "a reference to the instance of the type SomeType; and the instance cannot be modified through this reference".

This const modification can be considered as syntactic sugar and a fool-proof feature protecting the variable of the type const SomeType& from modification of the instance, but the value of the variable itself can be modified, as you can assign a different reference of the same type to it later on.

C++ references are well explained here, with their semantics and usage:
http://en.wikipedia.org/wiki/Reference_%28C%2B%2B%29[^].

—SA

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