C# is a strongly typed object-oriented language whose code visually resembles C++ (and Java). This decision by the C# language designers allows C++ developers to easily leverage their knowledge to quickly become productive in C#. C# syntax differs from C++ in some ways, but most of the differences between these languages are semantic and behavioral, stemming from differences in the runtime environments in which they execute.



C#

C# source code compiles into managed code. Managed code, as you may already know, is an intermediate language (IL) because it is halfway between the high-level language (C#) and the lowest-level language (assembly/machine code). At run time, the Common Language Runtime (CLR) compiles the code on the fly by using Just In Time (JIT) compiling. As with just about anything in engineering, this technique comes with its pros and cons. It may seem that an obvious con is the inefficiency of compiling the code at run time. This process is different from interpreting, which is typically used by scripting languages such as Perl and JScript. The JIT compiler doesn’t compile a function or method each and every time it’s called; it does so only the first time, and when it does, it produces machine code native to the platform on which it’s running. An obvious pro of JIT compiling is that the working set of the application is reduced, because the memory footprint of intermediate code is smaller. During the execution of the application, only the needed code is JIT-compiled. If your application contains printing code, for example, that code is not needed if the user never prints a document, and therefore the JIT compiler never compiles it. Moreover, the CLR can optimize the program’s execution on the fly at run time. For example, the CLR may determine a way to reduce page faults in the memory manager by rearranging compiled code in memory, and it could do all this at run time. Once you weigh all the pros together, you find that they outweigh the cons for most applications.



C++

Unlike C#, C++ code traditionally compiles into native code. Native code is the machine code that’s native to the processor for which the program was compiled. For the sake of discussion, assume that we’re talking about natively compiled C++ code rather than managed C++ which can be achieved by using C++/CLI. If you want your native C++ application to run on different platforms, such as on both a 32-bit platform and a 64-bit platform, you must compile it separately for each. The native binary output is generally not compatible across platforms.



IL, on the other hand, is compatible across platforms, because it, along with the Common Language Infrastructure (CLI) upon which the CLR is built, is a defined international standard. This standard is rapidly gaining traction and being implemented beyond the Microsoft Windows platform.



Included in the CLI standard is the Portable Executable (PE) file format for managed modules. Therefore, you can actually compile a C# program on a Windows platform and execute the output on both Windows and Linux without having to recompile, because even the file format is standardized. This degree of portability is extremely convenient and was in the hearts and minds of the COM/DCOM designers back in the day, but for various reasons, it failed to succeed across disparate platforms at this level. One of the major reasons for that failure is that COM lacked a sufficiently expressive and extensible mechanism for describing types and their dependencies. The CLI specification solves this nicely by introducing metadata.



CLR Garbage Collection

One of the key facilities in the CLR is the garbage collector (GC). The GC frees you from the burden of handling memory allocation and deallocation, which is where many software errors can occur. However, the GC doesn’t remove all resource-handling burdens from your plate. A file handle is a resource that must be freed when the consumer is finished with it, just as memory must be freed in the same way. The GC handles only memory resources directly. To handle resources other than memory, such as database connections and file handles, you can use a finalizer to free your resources when the GC notifies you that your object is being destroyed. However, an even better way is to use the Disposable pattern for this task.



The CLR references all objects of reference type indirectly, similar to the way you use pointers and references in C++, except without the pointer syntax. When you declare a variable of a reference type in C#, you actually reserve a storage location that has a type associated with it, either on the heap or on the stack, which stores the reference to the object. So when you copy an object reference in one variable into another variable, you end up with two variables referencing the same object. All reference type instances live on the managed heap. The CLR manages the location of these objects, and if it needs to move them around, it updates all the outstanding references to the moved objects to point to the new location. Also, value types exist in the CLR, and instances of them live on the stack or as a field of an object on the managed heap. Their usage comes with many restrictions and nuances. You normally use them when you need a lightweight structure to manage some related data. Value types are also useful when modeling an immutable chunk of data.



C# allows you to develop applications rapidly while dealing with fewer mundane details than in a C++ environment. At the same time, C# provides a language that feels familiar to either C++ or Java developers.



Source of Information : Apress Accelerated C Sharp 2008