对直接初始化和复制初始化感到困惑

I am confused with followed concepts:

我对以下概念感到困惑:

string str="123";

Some books say that: using "=" is copy initialization,

有些书说:使用“=”是复制初始化,

but some articles say: string str="123" is same as string str("123"). There is no doubt str("123") is directly initialization.

但有些文章说:string str =“123”与string str(“123”)相同。毫无疑问,str(“123”)是直接初始化的。

So which style for string str="123";?

那么字符串str =“123”的样式是什么?

How to judge which is copy initialization or directly initialization?

如何判断哪些是复制初始化还是直接初始化?

2 个解决方案

#1

It's simply a matter of grammar:

这只是一个语法问题:

T x = y; is copy-initialization, and

T x = y;是复制初始化,和
T x(y); is direct-initialization.

T x(y);是直接初始化。

This is true for any type T. What happens exactly depends on what sort of type T is. For primitive types (e.g. ints), the two are exactly the same. For class-types (such as std::string), the two are practically the same, though copy-initialization requires that a copy-constructor be accessible and non-explicit (though it will not actually be called in practice).

对于任何类型T都是如此。究竟发生了什么取决于T的类型。对于原始类型(例如整数),两者完全相同。对于类类型(例如std :: string),两者实际上是相同的,尽管复制初始化要求复制构造函数是可访问且非显式的(尽管实际上不会实际调用它)。

#2

Yes that is called copy initialization.

是的,称为复制初始化。

Instead of default constructing str and then constructing another string from "123" using string(const char*) and then assigning the two strings, the compiler just construct a string using string(const char*) with "123".

而不是默认构造str然后使用字符串(const char *)从“123”构造另一个字符串然后分配两个字符串,编译器只使用字符串(const char *)和“123”构造一个字符串。

string str="123" is same as string str("123"). There is no doubt str("123") is directly initial

string str =“123”与字符串str(“123”)相同。毫无疑问str(“123”)是直接初始的

However remember that is possible only if the corresponding constructor is not explicit.

但是请记住,只有相应的构造函数不明确时才可能。

#1