铸造：btw有什么区别。(Casting: What is the difference btw. T(value) and (T)value for built

铸造：btw有什么区别。(Casting: What is the difference btw. T(value) and (T)value for built-in types? [duplicate])

可能重复： C ++演员语法样式 （类型）值和类型（值）之间有什么区别？

在C ++中，当显式地将一个内置类型转换为另一个内置类型时，您可以编写：

int x = (int)c; int x = int(c); int d = (double)f; int d = double(f);

我知道(T)v是一个C风格的演员，我认为其他语法在技术上不是演员，但是其他语法是什么，它的语义是什么？ （以及在哪里使用？）

Possible Duplicates: C++ cast syntax styles What is the difference between (type)value and type(value) ?

In C++, when explicitly converting one built-in type to another, you can write:

int x = (int)c; int x = int(c); int d = (double)f; int d = double(f);

I known that (T)v is a C-style cast, and I think the other syntax isn't technically a cast, but what is the other syntax called and what are its semantics? (And where to use which?)

最满意答案

T(value)实际上是类型T的初始化，并且因为它是初始化，所以如果value的类型和T是可转换的，则可以发生隐式类型转换。 如果T是一个类对象，则调用其中一个构造函数，或者采用单个值的默认构造函数， T和value是可隐式转换类型，或者复制构造函数具有两个类型可隐式转换的相同条件。 正如您所指出的， (T)value是从value类型到类型T的C样式转换。 最后两者虽然如此，但在引擎盖下却几乎都做同样的事情

T var1 = T(value); T var2 = (T)value;

你得到完全相同的结果，即创建/返回类型为T的对象，用于初始化类型为T的l值。

T(value) is actually an initialization of the type T, and because it's an initialization, an implicit type conversion can take place if the type of value and T are convertible. If T is a class-object, then one of it's constructors is called, either a default constructor that takes a single value and T and value are implicitly convertible types, or the copy constructor with the same condition that the two types are implicitly convertible. (T)value, as you've noted, is a C-style cast from the type of value, to the type T. Both in the end though are pretty much doing the same thing under the hood since if you did

T var1 = T(value); T var2 = (T)value;

you'd get the exact same result, that is both create/return an object of type T which an be used to initialize an l-value of type T.