据我所知…

你的困难似乎在于决定你所听到的是否可信，当你试图评估这个网站上的回复时，这个困难将会重复。

你将如何判断人们在这里所说的比你最初听到的更可信还是更不可信?

一种方法是要求提供证据。

当有人声称“在某些领域c#被证明比c++快”时，问他们为什么这么说，让他们给你看测量结果，让他们给你看程序。有时他们只是犯了一个错误。有时你会发现他们只是在表达一种观点，而不是分享一些他们可以证明是正确的事情。

通常情况下，信息和观点会混淆在人们的说法中，你必须试着分清哪个是哪个。例如，从这个论坛的回复中:

"Take the benchmarks at http://shootout.alioth.debian.org/ with a great deal of scepticism, as these largely test arithmetic code, which is most likely not similar to your code at all." Ask yourself if you really understand what "these largely test arithmetic code" means, and then ask yourself if the author has actually shown you that his claim is true. "That's a rather useless test, since it really depends on how well the individual programs have been optimized; I've managed to speed up some of them by 4-6 times or more, making it clear that the comparison between unoptimized programs is rather silly." Ask yourself whether the author has actually shown you that he's managed to "speed up some of them by 4-6 times or more" - it's an easy claim to make!

垃圾收集是Java#不能用于实时系统的主要原因。

GC什么时候会发生? 需要多长时间?

这是不确定的。

快了5个橘子。或者更确切地说:不可能有一个(正确的)笼统的答案。c++是一种静态编译语言(但也有配置文件引导的优化)，c#在JIT编译器的帮助下运行。它们之间的差异如此之大，以至于像“快了多少”这样的问题都无法回答，甚至无法给出数量级。

没有严格的理由说明为什么基于字节码的语言(如c#或Java)不能像c++代码一样快。然而，c++代码在很长一段时间内都要快得多，今天在许多情况下仍然如此。这主要是因为更高级的JIT优化实现起来比较复杂，而真正酷的JIT优化现在才出现。

所以在很多情况下，c++更快。但这只是答案的一部分。c++实际上更快的情况是高度优化的程序，其中专业程序员彻底优化了代码。这不仅非常耗时(因此非常昂贵)，而且由于过度优化通常会导致错误。

On the other hand, code in interpreted languages gets faster in later versions of the runtime (.NET CLR or Java VM), without you doing anything. And there are a lot of useful optimizations JIT compilers can do that are simply impossible in languages with pointers. Also, some argue that garbage collection should generally be as fast or faster as manual memory management, and in many cases it is. You can generally implement and achieve all of this in C++ or C, but it's going to be much more complicated and error prone.

As Donald Knuth said, "premature optimization is the root of all evil". If you really know for sure that your application will mostly consist of very performance critical arithmetic, and that it will be the bottleneck, and it's certainly going to be faster in C++, and you're sure that C++ won't conflict with your other requirements, go for C++. In any other case, concentrate on first implementing your application correctly in whatever language suits you best, then find performance bottlenecks if it runs too slow, and then think about how to optimize the code. In the worst case, you might need to call out to C code through a foreign function interface, so you'll still have the ability to write critical parts in lower level language.

请记住，优化一个正确的程序相对容易，但更正一个优化的程序要难得多。

给出实际的速度优势百分比是不可能的，这在很大程度上取决于你的代码。在许多情况下，编程语言实现甚至不是瓶颈。请带着极大的怀疑态度使用http://benchmarksgame.alioth.debian.org/上的基准测试，因为这些测试的主要是算术代码，很可能与您的代码完全不同。

我知道这不是你想问的，但是c#通常比c++写得更快，这在商业环境中是一个很大的好处。

c++(或C)为您提供了对数据结构的细粒度控制。如果你想玩，你有这个选择。大型托管Java或。net应用程序(OWB, Visual Studio 2005)，它们使用Java/。NET库自带包袱。我曾见过OWB设计会话使用超过400 MB的RAM，立方体或ETL设计的bid也达到100 MB。

在可预测的工作负载上(例如重复一个过程多次的大多数基准测试)，JIT可以为您提供优化得足够好的代码，没有实际差别。

在大型应用程序上，差异与其说是JIT，不如说是代码本身使用的数据结构。当应用程序的内存很重时，您将获得较低的缓存使用效率。在现代cpu上，缓存丢失是非常昂贵的。C或c++的真正优势在于，您可以优化数据结构的使用，从而更好地使用CPU缓存。