我正在从C转到C ++，但没有得到这个类的创建 [英] I'm moving from C to C++ and I don't get this creation of a class

问题描述

我是C开发人员，所以我决定转向c ++作为主要语言，以扩大我的视野.通过"C ++编程语言"的研究，我看到了创建类的示例:

I'm a C developer and I decided to move to c++ as main language to enlarge my horizons. Studying from "The C++ Programming Language" I saw this example of the creation of a class:

class Vector {
public:
    Vector(int s) :elem{new double[s]}, sz{s} { }
    double& operator[](int i) { return elem[i]; }
    int size() { return sz; }
private:
    double* elem;
    int sz; 
};

我没有使用sz {s} {}

And I don't get the use of sz{s} { }

我们为什么使用 {} ?为什么在行尾没有; ?

Why do we use the {}? Why there is not ; at the end of the line?

推荐答案

由于延迟缩进.让我们写得更清楚:

Because of lazy indentation. Let's write it clearer:

class Vector
{
private:
    double* elem;
    int sz; 
public:
     Vector(int s)
         : elem{new double[s]}
         , sz{s}
     {
         // ctor body
     }

     // More class members
};

看到了吗?您神秘的 {} 只是构造函数的主体，而只是函数主体，就像在C语言中一样，函数并不以; 结尾.

See? Your mysterious {} are just the body of the constructor, that is just a function body, and as in C, functions do not end with a ;.

以:开头的怪异行是初始化列表，其中初始化成员变量和基类，也就是在其中将参数写入其构造函数的地方. sz {s} 只是此列表中的第二个元素.

The weird lines beginning with : is the initialization list, where member variables and base classes are initialized, that is where you write the areguments to their constructors. The sz{s} is just the second element in this list.

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