为什么C＃运行速度比C ++快？ [英] Why is C# running faster than C++?

问题描述

我不是在开玩笑。
我有一个C＃应用程序和一个C ++应用程序。他们做同样的事情，在完全相同的代码量...

I am not joking. I have a C# application, and a C++ application. They do they exact same thing, in the exact same amount of code...

...和C＃一个运行更快，不只是更快，但像10

...And the C# one is running faster, not just faster, but like 10 times faster.

这让我很奇怪，因为一个，我在调试器中运行C＃应用程序，这应该减慢C＃开始。然后，由于C＃是字节码与巨大的开销使用.NET编译成MSIL和一大堆额外的功能，这应该会放慢速度。

This struck me as weird, because for one, I was running the C# app in the debugger, which should slow C# down to begin with. Then, for the reason of that C# is bytecode with huge overhead using .NET compiled into MSIL with a bunch of extra features, that should slow it down. While C++ is just pure machine code.

这里是C＃代码：

static void main()
{
    ulong i = 0;
    while (i < 100000000000)
    {
        Console.WriteLine(i);
        i++;
    }
}

这是C ++代码

int main()
{
    usigned long i = 0;
    while (i < 100000000000)
    {
        cout << i << endl;
        i++;
    }
    return 0;
}

他们只是计数和显示一个数字。 C ++一个将在1000，而C＃一将在7000.（快7倍）

They are just counting and displaying a number. The C++ one would be at 1000, while the C# one would be at 7000. ( 7x faster)

我甚至尝试编译他们，并运行他们没有调试器使用命令提示符与命令： cplusplus.exe&& csharp.exe

I even tried compiling both of them, and running them without the debugger using command prompt with the command: cplusplus.exe && csharp.exe

是的，我知道也许这个问题是offtopic：P或者说不清楚是什么问题。 ：/
但是请有人向我解释这个问题。

Yeah, I know maybe this question is "offtopic" :P or maybe it is "not clear what's being asked for". :/ But please, someone explain this to me.

如果这很重要，我使用这个CPU：Intel i7 2.5 Ghz。

If this matters, I am using this CPU: Intel i7 2.5 Ghz.

编辑：
我做了 cout < i<< \ n; 创意，以及 std :: ios_base :: sync_with_stdio（false）; 在结果中。

I did the cout << i << "\n"; idea, plus the std::ios_base::sync_with_stdio(false); idea, without any luck or change in results.

编辑2：我试过C的printf（），它是多得多，更快。比C＃快3倍。

EDIT 2: I tried C's printf() and it was much, much faster. 3x faster than C#.

人们告诉我，IO流非常慢，所以我没有写入控制台尝试他们，C ++仍然明显快于C＃ 。

People told me that IO stream was very slow, so I then tried them both without writing to the console, and C++ was still significantly faster than C#.

总之，Writeline（）比cout快得多，printf（）比两者快得多。因此，写入控制台是唯一减慢速度的方法。

In conclusion, Writeline() is much faster than cout, and printf() is much faster than both. So writing to the console is the only thing that slows it down.

TLDR：printf（）胜利，控制台写入速度变慢。

TLDR: printf() wins, and console writing slows stuff down.

推荐答案

我认为你的评价不够仔细。我用C ++重新创建了你的测试，如下所示：

I think you've not been careful enough in your evaluation. I recreated your test with C++ proving massively faster as detailed below:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace CSScratch
{
    class Program
    {
        static void Main(string[] args)
        {
            ulong i = 0;
            while (i < 1000000)
            {
                Console.WriteLine(i);
                i++;
            }
        }
    }
}

在VS2013发布模式下构建到CSScratch.exe，然后我计时（在cygwin bash）输出重定向，所以文件系统写入时间不计数。结果相当一致，五次运行的最快 为：

I built the above in VS2013 Release mode to CSScratch.exe, which I then timed (under cygwin bash) with output redirected so file-system writing time wasn't counted. Results were fairly consistent, the fastest of five runs being:

time ./CSScratch.exe > NUL

real    0m17.175s
user    0m0.031s
sys     0m0.124s

C ++等价物：

#include <iostream>

int main()
{
    std::ios_base::sync_with_stdio(false);


    unsigned long i = 0;
    while (i < 1000000)
    {
        std::cout << i << '\n';
        i++;
    }
}

也用VS2013编译：

Also compiled with VS2013:

cl /EHsc /O2 output.cc
time ./output > NUL

最慢​​的

The slowest of five runs:

real    0m1.116s
user    0m0.000s
sys     0m0.109s

它比最快的C＃运行（17.175秒）更快（1.116秒）。

which is still faster (1.116 seconds) than the fastest of C# runs (17.175 seconds).

这两个版本的一些时间是通过加载/动态链接，初始化等。我将C ++版本修改为循环10倍以上 它仍然只需要9.327秒 - 大约是C＃需要十分之一工作量的时间的一半。

Some of the time for both versions is taken by loading / dynamic linking, initialisation etc.. I modified the C++ version to loop 10x more, and it still only took 9.327 seconds - about half the time C# needed for a tenth of the workload.

（您可以通过设置更大的输出缓冲区来进一步调整C ++版本，但通常不需要）。

(You could further tune the C++ version by setting a larger output buffer, but that's not normally needed).

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