C ++风格cast的性能命中？ [英] Performance hit from C++ style casts?

问题描述

我是新的C ++风格的演员，我担心使用C ++风格的演员会破坏我的应用程序的性能，因为我有一个

我听说过，我在中断服务程序中发现了实时关键的截止日期。一些cast甚至会抛出异常！

我想使用C ++风格的转换，因为它会使我的代码更健壮。但是，如果有任何性能影响，那么我可能不会使用C ++风格的转换，而是花更多的时间测试使用C风格的转换的代码。

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有没有人做过任何严格的测试/性能测试来比较C ++风格的转换和C风格的转换？

<你的结果是什么？

你得出了什么结论？

解决方案

cast可以概念性地替换为C风格的cast，将不会有开销。如果不能，如在 dynamic_cast 的情况下，没有C等效的，你必须以这种方式支付费用。

例如，以下代码：

  int x; 
 float f = 123.456; 
 
 x =（int）f; 
 x = static_cast< int>（f）; 
  

使用VC ++生成相同的代码：

  00401041 fld dword ptr [ebp-8] 
 00401044 call __ftol（0040110c）
 00401049 mov dword ptr [ebp-4]，eax 
  

可以抛出的唯一C ++类型是 dynamic_cast 当投射到参考。为了避免这种情况，转换为指针，如果转换失败，它将返回0。

I am new to C++ style casts and I am worried that using C++ style casts will ruin the performance of my application because I have a real-time-critical deadline in my interrupt-service-routine.

I heard that some casts will even throw exceptions!

I would like to use the C++ style casts because it would make my code more "robust". However, if there is any performance hit then I will probably not use C++ style casts and will instead spend more time testing the code that uses C-style casts.

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Has anyone done any rigorous testing/profiling to compare the performance of C++ style casts to C style casts?

What were your results?

What conclusions did you draw?

解决方案

If the C++ style cast can be conceptualy replaced by a C-style cast there will be no overhead. If it can't, as in the case of dynamic_cast, for which there is no C equivalent, you have to pay the cost one way or another.

As an example, the following code:

int x;
float f = 123.456;

x = (int) f;
x = static_cast<int>(f);

generates identical code for both casts with VC++ - code is:

00401041   fld         dword ptr [ebp-8]
00401044   call        __ftol (0040110c)
00401049   mov         dword ptr [ebp-4],eax

The only C++ cast that can throw is dynamic_cast when casting to a reference. To avoid this, cast to a pointer, which will return 0 if the cast fails.

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