&在函数声明返回类型 [英] & in function declaration return type

问题描述

什么是&在下面是什么意思？

What does the & mean in the following?

class Something
{
 public:
   int m_nValue;

   const int& GetValue() const { return m_nValue; }
   int& GetValue() { return m_nValue; }
};

此代码取自这里。

推荐答案

这意味着通过引用返回值：

   int& GetValue()
     ^ Means returns a reference of int

像

int i = 10;

int& GetValue() {
    int &j = i;
    return j;
}

注意：在C ++中有三种变量：

Note: In C++ you have three kinds of variables:

1. 值变量例如 int i = 10 。


2. 引用变量例如 int& j = i;
   引用变量创建其他变量的别名，都是同一内存位置的符号名称。


3. 地址变量： int * ptr =& i 。称为指针。指针变量用于保存变量的地址。

1. Value variable for example int i = 10.
2. Reference variable for example int &j = i; reference variable creates alias of other variable, both are symbolic names of same memory location.
3. Address variable: int* ptr = &i. called pointers. Pointer variables use for holding address of a variable.

声明中的参数

   Pointer:
           int  *ptr = &i;
                ^      ^  & is on the left side as an address operation
                |
                * For pointer variable.

   Reference:

           int &j = i;
               ^
               | & on the right side for reference

记住在C你只有两种变量值和地址）。引用变量在C ++中，引用很容易使用，如值变量和指针变量一样。

Remember in C you have only two kinds of variables value and address (pointer). Reference variables are in C++, and references are simple to use like value variables and as capable as pointer variables.

指针如下：

                      j = &i;

                      i                   j
                   +------+            +------+
                   | 10   |            | 200  |
                   +------+            +------+
                     202                 432

参考如下：

                   int &j = i;

                    i, j
                   +------+
                   | 10   |
                   +------+

没有给j分配内存。它是内存中相同位置的别名。

No memory is allocated for j. It's an alias of the same location in memory.

指针变量和引用变量之间的区别是什么？ >

What are the differences between pointer variable and reference variable in C++?

1. 指针可以重新分配任何次数，而引用初始化后无法重新分配。


2. 指针可以指向NULL，而引用永远不能指向NULL


3. 不能像指针一样获取引用的地址


4. 没有引用算术（但你可以取一个引用指向的对象的地址，并在其上做指针算术，如& obj + 5）。

1. A pointer can be re-assigned any number of times while a reference can not be reassigned after initialization.
2. A pointer can point to NULL while a reference can never point to NULL
3. You can’t take the address of a reference like you can with pointers
4. There’s no "reference arithmetics" (but you can take the address of an object pointed by a reference and do pointer arithmetics on it as in &obj + 5).

_{因为你评论过，你对指针和引用变量之间的差异有疑问，所以我强烈建议你从我给出的链接中读取相关页面我的回答。}

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