.NET fundamentals 4

Can I look at the IL for an assembly?
Yes. MS supply a tool called Ildasm which can be used to view the metadata and IL for an assembly.

Can source code be reverse-engineered from IL?
Yes, it is often relatively straightforward to regenerate high-level source (e.g. C#) from IL.

How can I stop my code being reverse-engineered from IL?
There is currently no simple way to stop code being reverse-engineered from IL. In future it is likely that IL obfuscation tools will become available, either from MS or from third parties. These tools work by 'optimising' the IL in such a way that reverse-engineering becomes much more difficult.
Of course if you are writing web services then reverse-engineering is not a problem as clients do not have access to your IL.

Is there built-in support for tracing/logging?
Yes, in the System.Diagnostics namespace. There are two main classes that deal with tracing - Debug and Trace. They both work in a similar way - the difference is that tracing from the Debug class only works in builds that have the DEBUG symbol defined, whereas tracing from the Trace class only works in builds that have the TRACE symbol defined. Typically this means that you should use System.Diagnostics.Trace.WriteLine for tracing that you want to work in debug and release builds, and System.Diagnostics.Debug.WriteLine for tracing that you want to work only in debug builds.

Can I redirect tracing to a file?
Yes. The Debug and Trace classes both have a Listeners property, which is a collection of sinks that receive the tracing that you send via Debug.WriteLine and Trace.WriteLine respectively. By default the Listeners collection contains a single sink, which is an instance of the DefaultTraceListener class. This sends output to the Win32 OutputDebugString() function and also the System.Diagnostics.Debugger.Log() method. This is useful when debugging, but if you're trying to trace a problem at a customer site, redirecting the output to a file is more appropriate. Fortunately, the TextWriterTraceListener class is provided for this purpose.

What are the contents of assembly?
In general, a static assembly can consist of four elements:
The assembly manifest, which contains assembly metadata.
Type metadata.
Microsoft intermediate language (MSIL) code that implements the types.
A set of resources.

What is GC (Garbage Collection) and how it works
One of the good features of the CLR is Garbage Collection, which runs in the background collecting unused object references, freeing us from having to ensure we always destroy them. In reality the time difference between you releasing the object instance and it being garbage collected is likely to be very small, since the GC is always running.
[The process of transitively tracing through all pointers to actively used objects in order to locate all objects that can be referenced, and then arranging to reuse any heap memory that was not found during this trace. The common language runtime garbage collector also compacts the memory that is in use to reduce the working space needed for the heap.]
Heap:
A portion of memory reserved for a program to use for the temporary storage of data structures whose existence or size cannot be determined until the program is running.

Differnce between Managed code and unmanaged code ?
Managed Code:
Code that runs under a "contract of cooperation" with the common language runtime. Managed code must supply the metadata necessary for the runtime to provide services such as memory management, cross-language integration, code access security, and
automatic lifetime control of objects. All code based on Microsoft intermediate language (MSIL) executes as managed code.
Un-Managed Code:
Code that is created without regard for the conventions and requirements of the common language runtime. Unmanaged code executes in the common language runtime environment with minimal services (for example, no garbage collection, limited debugging, and so on).

What is MSIL, IL, CTS and, CLR ?
MSIL: (Microsoft intermediate language)
When compiling to managed code, the compiler translates your source code into Microsoft intermediate language (MSIL), which is a CPU-independent set of instructions that can be efficiently converted to native code. MSIL includes instructions for loading, storing, initializing, and calling methods on objects, as well as instructions for arithmetic and logical operations, control flow, direct memory access, exception handling, and other operations. Before code can be executed, MSIL must be converted to CPU-specific code, usually by a just-in-time (JIT) compiler. Because the common language runtime supplies one or more JIT compilers for each computer architecture it supports, the same set of MSIL can be JIT-compiled and executed on any supported architecture.
When a compiler produces MSIL, it also produces metadata. Metadata describes the types in your code, including the definition of each type, the signatures of each type's members, the members that your code references, and other data that the runtime uses at execution time. The MSIL and metadata are contained in a portable executable (PE) file that is based on and extends the published Microsoft PE and Common Object File Format (COFF) used historically for executable content. This file format, which accommodates MSIL or native code as well as metadata, enables the operating system to recognize common language runtime images. The presence of metadata in the file along with the MSIL enables your code to describe itself, which means that there is no need for type libraries or Interface Definition Language (IDL). The runtime locates and extracts the metadata from the file as needed during execution.
IL: (Intermediate Language) A language used as the output of a number of compilers and as the input to a just-in-time (JIT) compiler. The common language runtime includes a JIT compiler for converting MSIL to native code.
CTS: (Common Type System) The specification that determines how the common language runtime defines, uses, and manages types
CLR: (Common Language Runtime) The engine at the core of managed code execution. The runtime supplies managed code with services such as cross-language integration, code access security, object lifetime management, and debugging and profiling support.

What is Reference type and value type ?
Reference Type:
Reference types are allocated on the managed CLR heap, just like object types.
A data type that is stored as a reference to the value's location. The value of a reference type is the location of the sequence of bits that represent the type's data. Reference types can be self-describing types, pointer types, or interface types
Value Type:
Value types are allocated on the stack just like primitive types in C/C++. Value types are not instantiated using new, and out of scope when the function they are defined within returns.
Value types in the CLR are defined as types that derive from system.valueType.
A data type that fully describes a value by specifying the sequence of bits that constitutes the value's representation. Type information for a value type instance is not stored with the instance at run time, but it is available in metadata. Value type instances can be treated as objects using boxing.

What is Boxing and unboxing ?
Boxing:
The conversion of a value type instance to an object, which implies that the instance will carry full type information at run time and will be allocated in the heap. The Microsoft intermediate language (MSIL) instruction set's box instruction converts a value type to an object by making a copy of the value type and embedding it in a newly allocated object.
Un-Boxing:
The conversion of an object instance to a value type.

What is JIT and how is works ?
An acronym for "just-in-time," a phrase that describes an action that is taken only when it becomes necessary, such as just-in-time compilation or just-in-time object activation

What is portable executable (PE) ?
The file format used for executable programs and for files to be linked together to form executable programs

What is strong name?
A name that consists of an assembly's identity—its simple text name, version number, and culture information (if provided)—strengthened by a public key and a digital signature generated over the assembly. Because the assembly manifest contains file hashes for all the files that constitute the assembly implementation, it is sufficient to generate the digital signature over just the one file in the assembly that contains the assembly manifest. Assemblies with the same strong name are expected to be identical

What is global assembly cache?
A machine-wide code cache that stores assemblies specifically installed to be shared by many applications on the computer. Applications deployed in the global assembly cache must have a strong name.

What is difference between constants, readonly and, static ?
Constants: The value can't be changed
Read-only: The value will be initialized only once from the constructor of the class.
Static: Value can be initialized once.

What is difference between shared and public?
An assembly that can be referenced by more than one application. An assembly must be explicitly built to be shared by giving it a cryptographically strong name.

What is namespace used for loading assemblies at run time and name the methods?
System.Reflection

What are the types of authentication in .net?
We have three types of authentication:
1. Form authentication
2. Windows authentication
3. Passport
This has to be declared in web.config file.

What is the difference between a Struct and a Class ?
The struct type is suitable for representing lightweight objects such as Point, Rectangle, and Color. Although it is possible to represent a point as a class, a struct is more efficient in some scenarios. For example, if you declare an array of 1000 Point objects, you will allocate additional memory for referencing each object. In this case, the struct is less expensive. When you create a struct object using the new operator, it gets created and the appropriate constructor is called. Unlike classes, structs can be instantiated without using the new operator. If you do not use new, the fields will remain unassigned and the object cannot be used until all of the fields are initialized. It is an error to declare a default (parameterless) constructor for a struct. A default constructor is always provided to initialize the struct members to their default values. It is an error to initialize an instance field in a struct. There is no inheritance for structs as there is for classes. A struct cannot inherit from another struct or class, and it cannot be the base of a class. Structs, however, inherit from the base class Object. A struct can implement interfaces, and it does that exactly as classes do.
A struct is a value type, while a class is a reference type.

How big is the datatype int in .NET?
32 bits.

How big is the char?
16 bits (Unicode).

How do you initiate a string without escaping each backslash?
Put an @ sign in front of the double-quoted string.

What's the access level of the visibility type internal?
Current application.

Explain encapsulation ?
The implementation is hidden, the interface is exposed.

What data type should you use if you want an 8-bit value that's signed?
sbyte.

Speaking of Boolean data types, what's different between C# and C/C++?
There's no conversion between 0 and false, as well as any other number and true, like in C/C++.

Where are the value-type variables allocated in the computer RAM?
Stack.

Where do the reference-type variables go in the RAM?
The references go on the stack, while the objects themselves go on the heap.

What is the difference between the value-type variables and reference-type variables in terms of garbage collection?
The value-type variables are not garbage-collected, they just fall off the stack when they fall out of scope, the reference-type objects are picked up by GC when their references go null.

How do you convert a string into an integer in .NET?
Int32.Parse(string)

How do you box a primitive data type variable?
Assign it to the object, pass an object.

Why do you need to box a primitive variable?
To pass it by reference.

What's the difference between Java and .NET garbage collectors?
Sun left the implementation of a specific garbage collector up to the JRE developer, so their performance varies widely, depending on whose JRE you're using. Microsoft standardized on their garbage collection.

How do you enforce garbage collection in .NET?
System.GC.Collect();

What's different about namespace declaration when comparing that to package declaration in Java?
No semicolon.