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Is C# really slower than say C++?

Asked 2011-03-16T13:49:45.630
86

I've been wondering about this issue for a while now.

Of course there are things in C# that aren't optimized for speed, so using those objects or language tweaks (like LinQ) may cause the code to be slower.

But if you don't use any of those tweaks, but just compare the same pieces of code in C# and C++ (It's easy to translate one to another). Will it really be that much slower ?

I've seen comparisons that show that C# might be even faster in some cases, because in theory the JIT compiler should optimize the code in real time and get better results:

Managed Or Unmanaged?

We should remember that the JIT compiler compiles the code at real time, but that's a 1-time overhead, the same code (once reached and compiled) doesn't need to be compiled again at run time.

The GC doesn't add a lot of overhead either, unless you create and destroy thousands of objects (like using String instead of StringBuilder). And doing that in C++ would also be costly.

Another point that I want to bring up is the better communication between DLLs introduced in .Net. The .Net platform communicates much better than Managed COM based DLLs.

I don't see any inherent reason why the language should be slower, and I don't really think that C# is slower than C++ (both from experience and lack of a good explanation)..

So, will a piece of the same code written in C# will be slower than the same code in C++ ?
In if so, then WHY ?

Some other reference (Which talk about that a bit, but with no explanation about WHY):

Why would you want to use C# if its slower than C++?

c# c++ performance
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3 Answers

43

Because you don't always need to use the (and I use this loosely) "fastest" language? I don't drive to work in a Ferrari just because it's faster...

answered 2011-03-16T13:52:17.190
6

BTW, time critical applications are not coded in C# or Java, primarily due to uncertainty of when the Garbage Collection will be performed.

In modern times, application or execution speed is not as important as was previously. Development schedules, correctness and robustness are higher priorities. A high speed version of an application is no good if it has lots of bugs, crashes a lot or worse, misses an opportunity to get to market or be deployed.

Since development schedules are a priority, new languages are coming out that speed up development. C# is one of these. C# also assists in correctness and robustness by removing features from C++ that cause common problems: one example is pointers.

The differences in execution speed of an application developed with C# and one developed using C++ is negligible on most platforms. This is due to the fact that the execution bottlenecks are not language dependent but usually depend on the operating system or I/O. For example if C++ performs a function in 5 ms but C# uses 2ms, and waiting for data takes 2 seconds, the time spent in the function is insignificant compared to the time waiting for data.

Choose a language that is best suited for the developers, platform and projects. Work towards the goals of correctness, robustness and deployment. The speed of an application should be treated as a bug: prioritize it, compare to other bugs, and fix as necessary.

answered 2011-03-16T19:05:36.873
1

Getting an exact answer to your question is not really possible unless you perform benchmarks on specific systems. However, it is still interesting to think about some fundamental differences between programming languages like C# and C++.

Compilation

Executing C# code requires an additional step where the code is JIT'ed. With regard to performance that will be in favor of C++. Also, the JIT compiler is only able to optimize the generated code within the unit of code that is JIT'ed (e.g. a method) while a C++ compiler can optimize across method calls using more aggressive techniques.

However, The JIT compiler is able to optimize the generated machine code to closely match the underlying hardware enabling it to take advantage of additional hardware features if they exist. To my knowledge the .NET JIT compiler doesn't do that but it would conceiveably be able to generate different code for Atom as opposed to Pentium CPU's.

Memory access

The garbage collected architecture can in many cases create more optimal memory access patterns than standard C++ code. If the memory area used for the first generation is small enough in can stay within the CPU cache increasing performance. If you create and destroy a lot of small objects the overhead of maintaing the managed heap may be smaller than what is required by the C++ runtime. Again, this is highly dependent on the application. A study Python of performance demonstrates that a specific managed Python application is able to scale much better than the compiled version as a result of more optimal memory access patterns.

answered 2011-05-11T12:40:11.453

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