不同形式的初始化 [英] Different forms of initialization

问题描述

我在读这本书叫做C ++的C ++之旅的Bjarne Stroustrup，里面提到基本上有两种初始化方式：

I was reading this book called 'A Tour of C++' by Bjarne Stroustrup and inside it is mentioned that there are basically two ways of initialization:

p int a = 5.2; // Stores truncated value

int a = 5.2; // Stores truncated value

int a {5.2}; //编译器抛出错误

int a{5.2}; // Compiler throws error

正如你所看到的，后一种方法更安全，更推荐。

As you can see, the latter method is safer and recommended.

但我注意到：

int a（5.2）;

int a(5.2);

也有效（与第二个版本不同，它不检查类型是否匹配）。

also works (and unlike the second version, it doesn't check if the type matches).

，可以有人请解释第三种情况，我的意思是，当它应该使用，它如何与第一种情况不同。

So, can someone please explain the third case, I mean, when it should be used and how it's different than the first case.

推荐答案

当你使用int a（5.2）;你正在调用int的构造函数，这是一个C ++方法来初始化变量。
这相当于其他人。
根据 http://www.cplusplus.com/doc/tutorial/variables/ ：

When you use int a(5.2); you are calling the constructor of int, which is a C++ method to initialize variables. This is equivalent to others. According to http://www.cplusplus.com/doc/tutorial/variables/ :

在C ++中，有三种方式来初始化变量。他们都是
等价的，并且让人联想到语言在
年的演变：

In C++, there are three ways to initialize variables. They are all equivalent and are reminiscent of the evolution of the language over the years:

第一个，被称为c样初始化（因为它是从C语言继承的
），包括附加等号后跟
变量初始化的值：

The first one, known as c-like initialization (because it is inherited from the C language), consists of appending an equal sign followed by the value to which the variable is initialized:

type identifier = initial_value;例如，声明一个变量
，类型int调用x，并从它声明的同一个
初始化为零值，我们可以这样写：

type identifier = initial_value; For example, to declare a variable of type int called x and initialize it to a value of zero from the same moment it is declared, we can write:

int x = 0;

第二种方法称为构造函数初始化（由
引入C ++语言）括号之间的初始值
（（））：

A second method, known as constructor initialization (introduced by the C++ language), encloses the initial value between parentheses (()):

类型标识符（initial_value）;例如：

type identifier (initial_value); For example:

int x (0);

最后，第三种方法称为统一初始化，类似于上面的
，使用花括号（{}）而不是括号（这个
是由C ++标准的修订版在2011年引入的）：

Finally, a third method, known as uniform initialization, similar to the above, but using curly braces ({}) instead of parentheses (this was introduced by the revision of the C++ standard, in 2011):

type identifier {initial_value} ;比如：

type identifier {initial_value}; For example:

int x {0};

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