static_cast真的和C / C ++样式一样快吗？ [英] Is static_cast really as fast as C/C++ style casts?
问题描述
大家好。简而言之，之间是否有任何性能差异：
float f = 10.0f;
int i = static_cast< int>（f）;
和
float f = 10.0f;
int i = int（f）;
我想问这个问题一段时间但是有多快
static_cast？我一直假设（没有证明）static_cast是作为模板实现的，只是包装了一个C / C ++风格的演员。然后
它是Josuttis的书，它说：
只有在定义了类型转换时才允许转换
大概这个测试是在编译时完成的吗？ />
另外，如果static_cast只是C / C ++演员的包装器，那么<br />
与reinterpret_cast的区别是什么？也许这些东西都是编译器
依赖，但任何信息都很有用。
谢谢，
David
Hi all. In short, is there any performance difference between:
float f = 10.0f;
int i = static_cast<int>(f);
and
float f = 10.0f;
int i = int(f);
I''ve been meaning to ask this for a while but just how fast is
static_cast? I had always assumed (without proof) that static_cast is
implemented as a template which just wraps a C/C++ style cast.But then
it the Josuttis book it says:
"The conversion is allowed only if a type conversion is defined"
Presumably then this test is done at compile time?
Also, if static_cast is just a wrapper around C/C++ casts then how does
it differ from reinterpret_cast? Maybe these things are compiler
dependant but any info is useful.
Thanks,
David
推荐答案
大家好。简而言之，之间是否有任何性能差异：
float f = 10.0f;
int i = static_cast< int>（f）;
和
float f = 10.0f;
int i = int（f）;
Hi all. In short, is there any performance difference between:
float f = 10.0f;
int i = static_cast<int>(f);
and
float f = 10.0f;
int i = int(f);
否，因为强制转换是一个编译时的概念 - 不是运行时概念。
两者都应该生成相同的机器代码。
No, because a "cast" is a compile-time concept -- not a runtime concept.
Both should produce identical machine code.
我'我一直想问这个问题，但是有多快这个问题
static_cast？
I''ve been meaning to ask this for a while but just how fast is
static_cast?
它没有速度。
It doesn''t have a speed.
我一直认为（没有证明）static_cast实现为
a模板，它只包含一个C / C ++风格的演员。然后它就是Josuttis
的书，它说：
"只有在定义了类型转换时才允许转换
大概这个测试是在编译时完成的吗？
I had always assumed (without proof) that static_cast is implemented as
a template which just wraps a C/C++ style cast.But then it the Josuttis
book it says:
"The conversion is allowed only if a type conversion is defined"
Presumably then this test is done at compile time?
是的。使用符合标准的编译器进行测试：
char * p = 0;
long i = static_cast< long>（p）;
你应该得到编译器错误。
Yes it is. Test it with a conforming compiler:
char *p = 0;
long i = static_cast<long>(p);
You should get a compiler error.
另外，如果static_cast只是C / C ++强制转换的包装，那么
它与reinterpret_cast有什么不同？也许这些东西都是编译器
依赖，但任何信息都很有用。
Also, if static_cast is just a wrapper around C/C++ casts then how does
it differ from reinterpret_cast? Maybe these things are compiler
dependant but any info is useful.
我在上面给你看的方式。有一些东西列出了static_cast
会让你做的事情，还有其他的东西，它不会让你这么做。对于它不会让你这么做的事情，你必须使用reinterpret_cast。
-
Frederick Gotham
In the way I showed you above. There''s a list of things which static_cast
WILL let you do, and others which it WON''T let you do. For the things it
won''t let you do, you must use reinterpret_cast.
--
Frederick Gotham
es ***** @ googlemail.com 写道：
es*****@googlemail.com wrote :
据推测，这个测试是在编译时完成的吗？
Presumably then this test is done at compile time?
是。
Yes.
>
>
好的，感谢输入。我很想写出正确的代码，但是如果可能的话，我不想要牺牲速度。好像我在这里好：-D
es ***** @ googlemail.com 写道：
Ok, thanks for the input. I''m keen to write correct code but don''t want
to sacrifice speed if possible. Seems like I''m ok here :-D
es*****@googlemail.com wrote:
大家好。简而言之，之间是否有任何性能差异：
float f = 10.0f;
int i = static_cast< int>（f）;
和
float f = 10.0f;
int i = int（f）;
我想问这个问题一段时间但是有多快
static_cast？我一直假设（没有证明）static_cast是作为模板实现的，只是包装了一个C / C ++风格的演员。然后
它是Josuttis的书，它说：
只有在定义了类型转换时才允许转换
大概这个测试是在编译时完成的吗？ />
另外，如果static_cast只是C / C ++演员的包装器，那么<br />
与reinterpret_cast的区别是什么？也许这些东西都是编译器
依赖但任何信息都很有用。
谢谢，
David
Hi all. In short, is there any performance difference between:
float f = 10.0f;
int i = static_cast<int>(f);
and
float f = 10.0f;
int i = int(f);
I''ve been meaning to ask this for a while but just how fast is
static_cast? I had always assumed (without proof) that static_cast is
implemented as a template which just wraps a C/C++ style cast.But then
it the Josuttis book it says:
"The conversion is allowed only if a type conversion is defined"
Presumably then this test is done at compile time?
Also, if static_cast is just a wrapper around C/C++ casts then how does
it differ from reinterpret_cast? Maybe these things are compiler
dependant but any info is useful.
Thanks,
David
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