What are core concept differences between C++ and C#?

Question

Let assume one knows C++, what are the main concepts that can confuse them/that work differently when using C#?

I do not mean the syntax differences but for example how references works, what "replaces" pointers, etc. or how the idea of managed code affects developer experience?

EDIT: Thanks to Chris for pointing out this great blog posts:

http://blogs.msdn.com/texblog/archive/2005/06/02/424588.aspx
http://www.thinkingparallel.com/2007/03/06/c-vs-c-a-checklist-from-a-c-programmers-point-of-view/

EDIT2:

http://www.charlespetzold.com/dotnet/

Answer 1

In C# every object is a reference. You never have to deal with pointers at all. Value types (int, float, bool...) are copied and objects are referenced. The only exception are structs which are value types in C#.

Value types can be referenced though using the "ref" keyword in the method declaration.

Also, .net has a garbage collector which automatically frees objects that are no longer used in your application. IMO in C# it is harder to keep track of where all of your memory goes. That is not to say that I don't like the language, however. .net also has a MASSIVE standard library which is well organized and can accomplish most of every task you can imagine.

C# is pure OO like Java - everything lives in a class unlike the psudo-OOness of C++.

Answer 2

The meaning of "struct" and "class" is very different in C++ and C#. In C++, a struct is a class where the default access is public, and in C# a struct denotes a "value type" where a class is always a "reference type".

Answer 3

C++ templates and C# generics look very similar at first look, and actually serve mostly the same purposes, but the knowledge is less transferable than you'd imagine at first thought.

Answer 4

c# apps run quicker by 6 months....

Answer 5

One of the main differences are the reference/value types in .NET. Classes are reference types, structs are value types. C++ programmers might think of references like strongly typed pointers, because the reference contains the address in the managed heap, like the pointer, except C++ heap is not managed of course. On the other side, value types are directly stored in the stack, no heap allocation there. And here comes another big concept in .NET - the heap is auto managed by the Garbage Collector (GC). The memory for all reference variables is allocated with the new operator like in C++, but freeing the memory is not responsibility of the programmer. When the memory is not referenced any more and the GC triggers, it's freed and the heap is defragmented. Again, this happens to reference types, value types are is the stack and after the method returns its stack is gone.
Added: For me the important thing is how this concept differences affect the development style generally. If we look at the usage of C++ and .NET, we see that C++ is used when performance is needed and .NET - when developer productivity is needed. Writing C# is easier, the large framework saves 90% (subjective of course) of the work, bugs are more rare. This makes it more suitable for so called enterprise solutions. But C++ is much better for creating drivers, embedded applications and 3D engines for example.

Answer 6

The intention of the languages are different.

C++ was designed as a systems programming language - close to the metal, where you don't pay for what you won't use. C# intends to offer a vast library to ease creation of applications.

This means you need a lot of code in C++ to obtain things you can do in one line in C# (or VB.Net or Boo or any emerging .NET language), but this also means you can optimize the code for a specific architecture.

C++ allows a mixture of OO, structured and generic (and meta-)programming. I'm not sure sure sure, but I believe C# generics are not fit for metaprogramming.

Answer 7

Constants

There is no concept of "const-correctness" in C#. Also, there are two versions of constants. Compile-time constants ("const") and runtime constants ("readonly")

Value Types and Reference Types

In C++ : All types are values, references are created to these values In C# : There are value types and reference types. This is a very important difference, as changing this will drastically affect the behavior of the code.

Dispose() pattern

For resource management (non-memory), instead of the RAII where we get resources in the constructor and release them in the destructor, one implements the Dispose pattern.

When using classes that implement the IDisposable interface, either:

a. call their Dispose() method or b. use the using keyword

using(ResourceHogger rh = new ResourceHogger())
{
   ... 
}

Answer 8

A somewhat surprising similarity to C++ is that in C# apps, despite being run in a garbage collected runtime, you can also leak memory, badly. ;)

Answer 9

One of the main differences not mentioned yet is the single inheritence model (like in java), you can only inherit from one parent class.

Answer 10

Everything we can write for an answer has been written elsewhere, like here, or here

Answer 11

If there's one thing that you need to be aware of when switching from C++ to C#:

Don't expect it to run on *nix (although you can give it a try)

On a more serious note, Microsoft may be changing their old ways, as indicated by the introduction Silverlight as cross-platform.

Answer 12

There is a resource out there that can be helpful: What the C or C++ Programmer Needs to Know About C# and the .NET Framework (aka .NET Book Zero) by Charles Petzold. ;-)

Answer 13

This is one of the questions where I'm really tempted just to say “wrong” – because basically, C# and C++ share (next to) no core concepts. Their names are intentionally similar, as is their syntax – but that's just a marketing trick.

C#'s core concepts say that it is an object-oriented, framework-supported language explicitly targeting Windows development. C# was developed to make RAD (rapid application development) in the tradition of VB6 possible, and offers facilities to work well with Smart Client (= classical windows) as well as web applications. Subsequent versions of C# have basically brought more of the same, albeit jumping on every marketing bandwagon along the way. Not that this is a bad thing, because it means that C# now has some really fancy features borrowed from functional programming. All in all, C# focuses on making programming even large systems relatively easy and safe (if something goes wrong, it does so on a high level; resources such as memory pointers are almost never corrupted).

C++ is fundamentally differently geared. C++ originally started out with the goal to be an object-oriented extension to C so there's at least some similarity to C# concepts: OOP. However, for at least 15 years, the development of C++ has parted from this path radically.

While OOP is still possible in C++, it is obviously no longer the main focus. C++ is called by its inventor (Stroustrup) “general purpose with a bias towards system programming” but that's rather unhelpful. C++ now really focuses on three main concepts: RAII (a very powerful mechanism to manage resources), template (meta-) programming and an unfortunate quasi-compatibility to C.

The latter is one of the reasons for C++' commercial success because it means that C++ can basically act as a drop-in replacement in large C systems that couldn't be rewritten from scratch. However, together with C++' meandering development pathway, it is also responsible for the convoluted syntax that is the target of a lot of (justified) criticism.

On the other hand, this also means that today C++ is in the rather unique position of offering a very high level of abstraction for the work with algorithms and data structures, at zero cost. Good C++ code can be just as efficient as good C or good FORTRAN code on the machine level (heck, even as efficient as good assembly code!).