C++ 静态转换与动态转换
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/1254777/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
static cast versus dynamic cast
提问by rayimag
Possible Duplicate:
Regular cast vs. static_cast vs. dynamic_cast
I don't quite get when to use static cast and when dynamic. Any explanation please?
我不太清楚什么时候使用静态转换，什么时候使用动态转换。请问有什么解释吗？
回答by Nick Meyer
Use dynamic_castwhen casting from a base class type to a derived class type. It checks that the object being cast is actually of the derived class type and returns a null pointer if the object is not of the desired type (unless you're casting to a reference type -- then it throws a bad_castexception).
使用dynamic_cast从基类转换为派生类类型时。它检查被强制转换的对象是否实际上是派生类类型，如果对象不是所需的类型，则返回一个空指针（除非您要强制转换为引用类型——然后它会抛出bad_cast异常）。
Use static_castif this extra check is not necessary. As Arkaitz said, since dynamic_castperforms the extra check, it requires RTTI information and thus has a greater runtime overhead, whereas static_castis performed at compile-time.
static_cast如果不需要此额外检查，请使用。正如 Arkaitz 所说，由于dynamic_cast执行额外检查，它需要 RTTI 信息，因此具有更大的运行时开销，而static_cast在编译时执行。
回答by xan
In some contexts, like this one, "static" refers to compile-time and "dynamic" refers to run-time.
在某些上下文中，像这样，“静态”指的是编译时，而“动态”指的是运行时。
For compile-time checking, use static_cast (limited to what the compiler knows). For run-time checking, use dynamic_cast (limited to classes with RTTI). For no checking, use reinterpret_cast.
对于编译时检查，请使用 static_cast（仅限于编译器知道的内容）。对于运行时检查，请使用 dynamic_cast（仅限于具有 RTTI 的类）。对于不检查，请使用 reinterpret_cast。
回答by Diaa Sami
dynamic_cast checks information available at run-time, such as RTTI, it also traverses class hierarchies to see if such cast is possible.
dynamic_cast 检查运行时可用的信息，例如 RTTI，它还遍历类层次结构以查看此类转换是否可行。
回答by Jesse Vogt
static_castis similar to the old C style cast and can be applied to just about anything. static_castwould be used when you certain of the types in question. For example, I usually use a static_castwhen casting between intand enum.
static_cast类似于旧的 C 风格转换，几乎可以应用于任何东西。static_cast当您有问题的某些类型时将使用。例如，我通常static_cast在int和之间转换时使用 a enum。
dynamic_castcan only be used with pointers and references. On failure to cast, a null pointer is returned. dynamic_castis generally used when resolving pointers to classes used in inheritance where you want to make sure the pointer you are casting is of the expected type.
dynamic_cast只能与指针和引用一起使用。如果转换失败，则返回空指针。dynamic_cast通常在解析指向继承中使用的类的指针时使用，您希望确保您正在转换的指针是预期的类型。
Also check out C++ : Documentation : C++ Language Tutorial : Type Casting
回答by xtofl
Static casting is done by the compiler: it treats the result as the target type, no matter what. You do this when you're absolutely sure about the argument being of the target type.
静态转换由编译器完成：无论如何，它都将结果视为目标类型。当您完全确定参数是目标类型时，您可以这样做。
Dynamic casting is done at runtime, and thus requires runtime type information. You do this when you're unsure about the type you have: the cast may fail, which is shown by the return value being null. It can also only be done for pointers and references.
动态转换在运行时完成，因此需要运行时类型信息。当您不确定您拥有的类型时，您可以这样做：转换可能会失败，这表现为返回值为 null。它也只能用于指针和引用。
回答by Arkaitz Jimenez
Dynamic cast requires RTTI and does some magic compared to static cast. static_cast is just a compile time cast, checks if origin class can be promoted to the casted class by some simple rules as inheritance.
动态转换需要 RTTI 并且与静态转换相比有一些神奇之处。static_cast 只是一个编译时转换，检查源类是否可以通过一些简单的规则提升为转换类，如继承。
For example, in cases of virtual inheritance only dynamic_cast can resolve the situation.
例如，在虚拟继承的情况下，只有 dynamic_cast 可以解决这种情况。
Apart, dynamic_cast will return NULL if the cast is not possible, so you can take a different decision.
另外，如果无法进行强制转换，则 dynamic_cast 将返回 NULL，因此您可以做出不同的决定。
In the other hand, dynamic_cast is slower, as it implies some code being executed, and as said previously, it needs RTTI enabled which increases the size of the binaries.
另一方面，dynamic_cast 速度较慢，因为它意味着正在执行一些代码，并且如前所述，它需要启用 RTTI，这会增加二进制文件的大小。
回答by faya
If you are talking about C++. Then static_cast is not safe type of casting. It can cast to your type but if its wrong it will not throw any error/message. So you will get bad object from that. And the dynamic_cast is throwing error if the casting failed :) Hope this helps ! :)
如果你在谈论 C++。那么 static_cast 不是安全的类型转换。它可以转换为您的类型，但如果错误，则不会抛出任何错误/消息。所以你会从中得到不好的对象。如果转换失败，则 dynamic_cast 会抛出错误:) 希望这会有所帮助！:)
