How much faster is C++ than C#?

Question

Or is it now the other way around?

From what I've heard there are some areas in which C# proves to be faster than C++, but I've never had the guts to test it by myself.

Thought any of you could explain these differences in detail or point me to the right place for information on this.

Answer 1

It's five oranges faster. Or rather: there can be no (correct) blanket answer. C++ is a statically compiled language (but then, there's profile guided optimization, too), C# runs aided by a JIT compiler. There are so many differences that questions like “how much faster” cannot be answered, not even by giving orders of magnitude.

Answer 2

It's an extremely vague question without real definitive answers.

For example; I'd rather play 3D-games that are created in C++ than in C#, because the performance is certainly a lot better. (And I know XNA, etc., but it comes no way near the real thing).

On the other hand, as previously mentioned; you should develop in a language that lets you do what you want quickly, and then if necessary optimize.

Answer 3

Applications that require intensive memory access eg. image manipulation are usually better off written in unmanaged environment (C++) than managed (C#). Optimized inner loops with pointer arithmetics are much easier to have control of in C++. In C# you might need to resort to unsafe code to even get near the same performance.

Answer 4

The garbage collection is the main reason Java# CANNOT be used for real-time systems.

1. When will the GC happen?

2. How long will it take?

This is non-deterministic.

Answer 5

There is no strict reason why a bytecode based language like C# or Java that has a JIT cannot be as fast as C++ code. However C++ code used to be significantly faster for a long time, and also today still is in many cases. This is mainly due to the more advanced JIT optimizations being complicated to implement, and the really cool ones are only arriving just now.

So C++ is faster, in many cases. But this is only part of the answer. The cases where C++ is actually faster, are highly optimized programs, where expert programmers thoroughly optimized the hell out of the code. This is not only very time consuming (and thus expensive), but also commonly leads to errors due to over-optimizations.

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.

Keep in mind that it's relatively easy to optimize a correct program, but much harder to correct an optimized program.

Giving actual percentages of speed advantages is impossible, it largely depends on your code. In many cases, the programming language implementation isn't even the bottleneck. Take the benchmarks at http://benchmarksgame.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.

Answer 6

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.