在带有static_cast的const-cast和"this"的const_cast之间添加C-ness的C ++区别.目的? [英] C++ difference between adding const-ness with static_cast and const_cast of "this" object?

问题描述

按照Scott Meyers的说法，为防止getter的const版本和getter的非const版本中的代码重复出现，请从非const版本中调用方法的const版本: static_cast< constA&>(* this).Methodology(); 然而，由于我输入的Visual Assist X Intellisense过于狂热，导致意外使用: const_cast< const A&>(* this).Methodology(); 正常运行.

As per Scott Meyers, to prevent repetition of code in the const version of a getter and the non-const version of a getter, call the const version of the method from the non-const version: static_cast<const A&>(*this).Methodology(); however, in accidental usage due to an overzealous Visual Assist X Intellisense I typed: const_cast<const A&>(*this).Methodology(); and it worked just fine.

在这种情况下，使用特定演员表有什么区别?

What are any and all differences in this case with using a particular cast?

正在使用的IDE:Visual Studio 2010.

IDE in use: Visual Studio 2010.

推荐答案

假定 this 的类型为 A * ，没有区别.

Assuming that the type of this is A*, there is no difference.

通常 const_cast 可以丢弃 const 说明符(从任何级别的间接寻址或模板参数开始)

In general const_cast can cast aways the const specifier (from any level of indirection or template parameter)

static_cast<> 可以将一种类型转换为另一种类型.

static_cast<> can cast a type to another if the target type is in the source's type hierarchy.

他们不能做彼此的工作.

They cannot do each other's work.

它们在您的情况下都起作用的原因是因为您引入了 const-ness，而不是将其删除(从函数的非const版本中调用此是 A * ，没有const).你也可以写

The reason they both worked in your case is because you have introduced const-ness, as opposed to having taken it away (calling from the non-const version of the function the type of this is A*, no const). You could just as well have written

const A& tmp = *this;
tmp.Methodology();

，它不需要任何转换就可以工作.强制转换是为了方便和简洁而不必引入新变量.

and it would have worked without the need for any casting. The casting is used for convenience and terseness to not have to introduce a new variable.

注意:知道要转换为正确的类型时，您可以在此处使用 static_cast<> .在其他情况下(不确定时)，您需要使用 dynamic_cast<> 进行运行时类型检查以确保转换有效

Note: you can use static_cast<> here as you know that you are casting to the right type. In other cases (when you cannot be sure) you need to use dynamic_cast<> that does a runtime type check to ensure the conversion is valid

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