何时使用c++中的哪个数据成员初始化

Considering this program:

考虑到这个项目:

#include <iostream>

class C
{
public:
    C(void): a(1)
    { a=2; }
    int a{3};
};

int main(void)
{
    C c{};
    std::cout << c.a; // 2
}

I can see three forms of data member initialization:

我可以看到数据成员初始化的三种形式:

using a member initializer list
使用成员初始化器列表。
using the Constructor
使用构造函数
using a declaration in the class body
在类主体中使用声明

When to use which?

什么时候使用哪个?

2 个解决方案

#1

1: Using a declaration in the class body

1:在类主体中使用声明。

You should use this when the member will always be initialized with the same value, and it doesn't make sense to have to explicitly write that for each constructor.

当成员总是用相同的值初始化时，您应该使用这个方法，并且必须为每个构造函数显式地编写这个值是没有意义的。

2: Using a member initializer list

2:使用成员初始化列表

The member initializer list is obviously necessary for a member that lacks a default constructor, but aside from that, if you're initializing a member based on the constructor, it makes sense to do it here.

成员初始化器列表对于缺少默认构造函数的成员显然是必要的，但是除此之外，如果您正在基于构造函数初始化成员，那么在这里这样做是有意义的。

3: Using the constructor body

3:使用构造函数体

The constructor body is more useful for logic that can't be performed in a single statement (in the init-list). However, I don't think there is much difference between initializing a POD in the member initializer list or the constructor body.

构造函数体对于不能在单个语句(在init-list中)中执行的逻辑更有用。但是，我认为在成员初始化列表中初始化POD和构造函数主体之间没有太大的区别。

#2

My suggestion is to use:

我的建议是:

int a{3};

This makes sure that a is initialized to 3 no matter how many constructors you have in the class.

这将确保无论类中有多少构造函数，a都被初始化为3。

My second choice will be to use the member initialization list.

我的第二个选择是使用成员初始化列表。

c(void) : a(1) {}

The third option, using code to set the value of a member variable, should be avoided.

第三个选项，使用代码来设置成员变量的值，应该避免。

#1