c#和c++在性能方面有一些主要的区别:

c#是基于GC /堆的。分配和GC本身是内存访问的非局部性开销 多年来，c++优化器已经变得非常好。JIT编译器无法达到相同的级别，因为它们只有有限的编译时间，并且看不到全局作用域

除此之外，程序员的能力也很重要。我见过一些糟糕的c++代码，其中的类通过值作为参数传递。在c++中，如果你不知道自己在做什么，实际上会让性能变差。

我发现2020年4月读过:https://www.quora.com/Why-is-C-so-slow-compared-to-Python，作者是一位拥有15年以上软件开发经验的现实世界的程序员。

它指出，c#通常较慢，因为它被编译为公共中间语言(CIL)，而不是像c++那样的机器代码。然后，CIL通过公共语言运行库(CLR)输出机器代码。但是，如果您继续执行c#，它将获取机器代码的输出并缓存它，以便为下次执行保存机器代码。总而言之，如果多次执行，c#会更快，因为它是多次执行后的机器代码。

也有评论说，一个优秀的c++程序员可以做一些耗时的优化，但最终会被优化。

需要大量内存访问的应用程序。图像处理通常更适合在非托管环境(c++)而不是托管环境(c#)中编写。使用指针算法优化的内循环在c++中更容易控制。在c#中，你可能需要使用不安全的代码来获得相同的性能。

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。

We have had to determine if C# was comparable to C++ in performance and I wrote some test programs for that (using Visual Studio 2005 for both languages). It turned out that without garbage collection and only considering the language (not the framework) C# has basically the same performance as C++. Memory allocation is way faster in C# than in C++ and C# has a slight edge in determinism when data sizes are increased beyond cache line boundaries. However, all of this had eventually to be paid for and there is a huge cost in the form of non-deterministic performance hits for C# due to garbage collection.

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。