DLL Speed

Majid Kamali

Hi.
Is it important that in which language, a DLL written with?
I mean, DLLs written in native C++ are faster or DLLs written in C#.NET? Because Native C++ is much faster that C#.

5 Replies

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Vulpes15y ago
Accepted answer
When speed tests are done on code written in different languages, there's a tendency to use simple algorithms which involve array or string manipulation.

Unmanaged C++ always shows up well in these tests because it uses pointers to do the manipulations and doesn't check whether those pointers are addressing memory which is outside the bounds of the array or string.

In contrast, C# - which is an inherently 'safe' language - does do bounds checking for every array or string access which slows down the code.

However, if you use 'unsafe' code in C# then there's no bounds checking and the results are usually much closer. Implementing 'time critical algorithms' was after all one of the reasons why unsafe code was included in C# in the first place.

Even when you use unsafe code, C++ still usually has the edge on speed because the compiler can do more optimizations than are feasible with the 'just in time' compiler used by .NET applications.

However, in 'real world' applications, these differences tend to get dwarfed by other factors such as database access as Mahesh and Sam have already pointed out.

Incidentally, it was claimed when it first came out that C++/CLI (which superseded Managed Extensions for C++), was slightly faster than C# because, when generating the IL, the compiler did a few more optimizations which improved the quality of the JIT'ed code. However, this does not seem to have been borme out in practice and I've never found there to be much difference either way.
Majid Kamali15y ago
Thanks to every one.
Sam Hobbs15y ago
As Mahesh says, it depends. I think that the example that you have is not representative. If the C# program is doing a database connection differently from how your C++ program did it then it is not a reasonable comparison. Normally C# will connect to a database much faster than that.

You might think that C++ is faster because it is compiled to machine code and C# is not, but C# does get compiled to machine code. You might be able to write C++ programs taht are more efficient but you need to be experienced and knowledgeable to be successful. Note that your time is also expensive and spending a lot of your time to save a little machine time might be considered poor performance, especially if someone is paying you to do the work.
Majid Kamali15y ago
Something like database connectivity is easier to develop in C# but I think, even in this case, C++ is faster. I wrote a console program in native C++ and it took less than a second to answer, but I wrote it in C# console and it even took 15 seconds.
BTW, in a program, between what you said (between low level and high level code), which is better?
Thanks
Mahesh Chand15y ago
This is untrue. It all depends on what exactly are you doing. Also, it is not true that C++ is faster than C#. Again, it depends on what exactly are you doing. For example, a DLL that uses and talk to hardware (low level machine) in C++ may be faster than C# but a DLL that has database connectivity may be faster in C# than C++.