(B)What is an IL?
Twist: - What is MSIL or CIL, What is JIT?
(IL)Intermediate Language is also known as MSIL (Microsoft Intermediate Language) or CIL
(Common Intermediate Language). All .NET source code is compiled to IL. IL is then converted
to machine code at the point where the software is installed, or at run-time by a Just-In-Time
(JIT) compiler.
(B)What is a CLR?
Full form of CLR is Common Language Runtime and it forms the heart of the .NET framework.
All Languages have runtime and it is the responsibility of the runtime to take care of the code
execution of the program. For example, VC++ has MSCRT40.DLL, VB6 has MSVBVM60.DLL,
and Java has Java Virtual Machine etc. Similarly, .NET has CLR. Following are the
responsibilities of CLR
• Garbage Collection: - CLR automatically manages memory thus eliminating
memory leaks. When objects are not referred, GC automatically releases those
memories thus providing efficient memory management.
• Code Access Security: - CAS grants rights to program depending on the security
configuration of the machine. Example the program has rights to edit or create a
new file but the security configuration of machine does not allow the program to
delete a file. CAS will take care that the code runs under the environment of
machines security configuration.
• Code Verification: - This ensures proper code execution and type safety while the
code runs. It prevents the source code to perform illegal operation such as accessing
invalid memory locations etc.
• IL (Intermediate language)-to-native translators and optimizer’s:- CLR uses
JIT, compiles the IL code to machine code, and then executes. CLR also determines
depending on platform what is optimized way of running the IL code.
(B)What is CTS?
In order that two language communicate smoothly CLR has CTS (Common Type
System).Example in VB you have “Integer” and in C++ you have “long” these datatypes are not
compatible so the interfacing between them is very complicated. In order that these two different
languages communicate Microsoft introduced Common Type System. So “Integer” data type in
VB6 and “int” data type in C++ will convert it to System.int32, which is data type of CTS. CLS,
which is covered in the coming question, is subset of CTS.
Note: If you have undergone COM programming period interfacing VB6
application with VC++ application was a real pain as the datatype of
both languages did not have a common ground where they can come and
interface, by having CTS interfacing is smooth.
(B)What is a CLS (Common Language Specification)?
This is a subset of the CTS, which all .NET languages are expected to support. It was always a
dream of Microsoft to unite all different languages in to one umbrella and CLS is one-step
towards that. Microsoft has defined CLS, which are nothing but guidelines, that language should
follow so that it can communicate with other .NET languages in a seamless manner.
(B)What is a Managed Code?
Managed code runs inside the environment of CLR i.e. .NET runtime. In short, all IL are
managed code. However, if you are using some third party software example VB6 or VC++
component they are unmanaged code, as .NET runtime (CLR) does not have control over the
source code execution of these languages.
(B)What is a Assembly?
• Assembly is unit of deployment like EXE or a DLL.
• An assembly consists of one or more files (dlls, exe’s, html files etc.), and
represents a group of resources, type definitions, and implementations of those
types. An assembly may also contain references to other assemblies. These
resources, types and references are described in a block of data called a manifest.
The manifest is part of the assembly, thus making the assembly self-describing.
• An assembly is completely self-describing. An assembly contains metadata
information, which is used by the CLR for everything from type checking an
security to actually invoking the components methods. As all information is in
the assembly itself, it is independent of registry. This is the basic advantage as
compared to COM where the version was stored in registry.
• Multiple versions can be deployed side by side in different folders. These different
versions can execute at the same time without interfering with each other.
Assemblies can be private or shared. For private assembly deployment, the
assembly is copied to the same directory as the client program that references it. No
registration is needed, and no fancy installation program is required. When the
component is removed, no registry cleanup is needed, and no uninstall program is
required. Just delete it from the hard drive.
• In shared assembly deployment, an assembly is installed in the Global Assembly
Cache (or GAC). The GAC contains shared assemblies that are globally accessible
to all .NET applications on the machine.
(A) What are the different types of Assembly?
There are two types of assembly Private and Public assembly. A private assembly is normally
used by a single application, and is stored in the application's directory, or a sub-directory
beneath. A shared assembly is normally stored in the global assembly cache, which is a repository
of assemblies maintained by the .NET runtime. Shared assemblies are usually libraries of code,
which many applications will find useful, e.g. Crystal report classes that will be used by all
application for Reports.
(B) What is NameSpace?
Namespace has two basic functionality:-
• NameSpace Logically group types, example System.Web.UI logically groups UI
related features.
• In Object Oriented world, many times it is possible that programmers will use the
same class name. Qualifying NameSpace with class name can avoid this collision.
(B) What is Difference between NameSpace and Assembly?
Following are the differences between namespace and assembly:
• Assembly is physical grouping of logical units, Namespace, logically groups
classes.
• Namespace can span multiple assembly.
(A) If you want to view an Assembly how do you go about it?
Twist: What is ILDASM?
When it comes to understanding of internals, nothing can beat ILDASM. ILDASM converts the
whole ‘exe’ or ‘dll’ in to IL code. To run ILDASM you have to go to ‘C:\Program
Files\Microsoft Visual Studio .NET 2003\SDK\v1.1\Bin’. Note that we had v1.1 you have to
probably change it depending on the type of framework version you have.
If you run IDASM.EXE from the path you will be popped with the IDASM exe program as
shown in figure ILDASM. Click on file and browse to the respective directory for the DLL whose
assembly you want to view. After you select the DLL you will be popped with a tree view details
of the DLL as shown in figure ILDASM. On double clicking on manifest, you will be able to
view details of assembly, internal IL code etc as shown in Figure ‘Manifest View’.
Note : The version number are in the manifest itself which is defined
with the DLL or EXE thus making deployment much easier as compared to
COM where the information was stored in registry. Note the version
information in Figure Manifest view.
You can expand the tree for detail information regarding the DLL like methods, properties,
functions etc.
Figure: - 1.1 ILDASM
Figure: - 1.2 Manifest View
(A) What is Manifest?
Assembly metadata is stored in Manifest. Manifest contains all the metadata needed to do the
following things (See Figure Manifest View for more details):
• Version of assembly.
• Security identity.
• Scope of the assembly.
• Resolve references to resources and classes.
The assembly manifest can be stored in a PE file either (an .exe or) .dll with Microsoft
intermediate language (MSIL code with Microsoft intermediate language (MSIL) code or in a
stand-alone PE file, that contains only assembly manifest information.
(B) Where is version information stored of an assembly?
Version information is stored in assembly inside the manifest.
(I) Is versioning applicable to private assemblies?
Versioning concept is only applicable to global assembly cache (GAC) as private assembly lie in
their individual folders. This does not mean versioning is not needed , you can still version it to
have better version control on the project.
(B) What is GAC?
Twist: In what situations will you register .NET assembly in GAC?
GAC (Global Assembly Cache) is where all shared .NET assembly reside. GAC is used in the
following situations:-
• If the application has to be shared among several application.
• If the assembly has some special security, requirements like only administrators can
remove the assembly. If the assembly is private then a simple delete of assembly
the assembly file will remove the assembly.
Note:- Registering .NET assembly in GAC can lead to the old problem of
DLL hell, where COM version was stored in central registry. So GAC
should be used when absolutely necessary.
(I) what is the concept of strong names?
Twist: - How do we generate strong names?
Twist: - What is use the of SN.EXE?
Twist: - How do we apply strong names to assembly?
Twist: - How do you sign an assembly?
Strong name is similar to GUID (It is supposed to be unique in space and time) in COM
components. Strong Name is only needed when we need to deploy assembly in GAC. Strong
Names helps GAC to differentiate between two versions. Strong names use public key
cryptography (PKC) to ensure that no one can spoof it.PKC use public key and private key
concept.
Following are the step to generate a strong name and sign a assembly:-
• Go to “Visual Studio Command Prompt”. See the below figure “Visual studio Command
prompt”. Note the samples are compiled in 2005 but 2003 users do not have to worry
about it. Same type of command prompt will be seen in 2003 also.
Figure: - 1.3 Visual Studio Command Prompt
• Once you are in command, prompt type sn.exe -k “c:\test.snk”.
Figure: - 1.4 Running SN.EXE
Figure: - 1.5 Successful output of SN.EXE
Figure: - 1.6 Sample view of test.snk file
• After generation of the file you can view the SNK file in a simple notepad
• After the SNK file is generated its time to sign the project with this SNK file.
Figure: - 1.7 Click on project & then click on “classlibrary1 properties” menu to sign the assembly
• Click on project -- properties and the browse the SNK file from the respective folder
and compile the project.
Figure: - 1.8 Click on ‘Use a key file’ to sign the assembly with strong name
(I) How to add and remove an assembly from GAC?
There are two ways to install .NET assembly in GAC:-
• Using Microsoft Installer Package. You can get download of installer from
http://www.microsoft.com.
• Using Gacutil. Go to “Visual Studio Command Prompt” and type “gacutil –i
(assembly name)”, where (assembly name) is the DLL name of the project.
(B) What is Delay signing?
During development process you will need strong name keys to be exposed to developer which is
not a good practice from security aspect point of view.In such situations you can assign the key
later on and during development you an use delay signing
Following is process to delay sign an assembly:
• First obtain your string name keys using SN.EXE.
• Annotate the source code for the assembly with two custom attributes from
System.Reflection: AssemblyKeyFileAttribute, which passes the name of the file
containing the public key as a parameter to its constructor.
AssemblyDelaySignAttribute, which indicates that delay signing, is being used by
passing true as a parameter to its constructor. For example as shown below:
[Visual Basic]
[C#]
[Assembly: AssemblyKeyFileAttribute ("myKey.snk")]
[Assembly: AssemblyDelaySignAttribute (true)]
The compiler inserts the public key into the assembly manifest and reserves space in the PE file
for the full strong name signature. The real public key must be stored while the assembly is built
so that other assemblies that reference this assembly can obtain the key to store in their own
assembly reference.
• Because the assembly does not have a valid strong name signature, the verification of
that signature must be turned off. You can do this by using the –Vr option with the
Strong Name tool. The following example turns off verification for an assembly called
myAssembly.dll.
Sn –Vr myAssembly.dll
• Just before shipping, you submit the assembly to your organization signing authority
for the actual strong name signing using the –R option with the Strong Name tool. The
following example signs an assembly called myAssembly.dll with a strong name using the
sgKey.snk key pair.
Sn -R myAssembly.dll sgKey.snk
(B) What is garbage collection?
Garbage collection is a CLR feature, which automatically manages memory. Programmers forget
to release the objects while coding ... Laziness (Remember in VB6 where one of the good
practices is to set object to nothing). CLR automatically releases objects when they are no longer
in use and refernced. CLR runs on non-deterministic to see the unused objects and cleans them.
One side effect of this non-deterministic feature is that we cannot assume an object is destroyed
when it goes out of the scope of a function. We should avoid using destructors because before GC
destroys the object it first executes destructor in that case it will have to wait for code to release
the unmanaged resource. This results in additional delays in GC. So it is recommended to
implement IDisposable interface, write cleanup code in Dispose method, and call
GC.SuppressFinalize method. Its like instructing GC not to call your constructor. For more details
read why is it preferred to not use finalize for clean up? in OOPS chapter..
(I) Can we force garbage collector to run?
System.GC.Collect () forces garbage collector to run. This is not recommended but can be used if
situations arise.
(B) What is reflection?
All .NET assemblies have metadata information stored about the types defined in modules. This
metadata information can be accessed by mechanism called as “Reflection”. System. Reflection
can be used to browse through the metadata information.
Using reflection, you can also dynamically invoke methods using System.Type.Invokemember.
Below is sample source code if needed you can also get this code from CD provided, go to
“Source code” folder in “Reflection Sample” folder.
Public Class Form1
Private Sub Form1_Load (ByVal sender As System. Object, ByVal e as
System.EventArgs) Handles MyBase.Load
Dim Pobjtype As Type
Dim PobjObject As Object
Dim PobjButtons As New Windows.Forms.Button ()
Pobjtype = PobjButtons.GetType ()
For Each PobjObject in Pobjtype.GetMembers
LstDisplay.Items.Add (PobjObject.ToString ())
Next
End Sub
End Class
Note:- Sample source code is compiled using VB.NET 2005.
Figure:- 1.9 Sample reflection display
Sample source code uses reflection to browse through “Button” class of “Windows.Forms”. If
you compile and run the program following is output as shown in “Sample Reflection Display”.
Using this reflection, you can also dynamically invoke a method using
“System.Type.InvokeMember”.
Note:- System.Type.InvokeMember is left as homework for readers.
Believe me you will enjoy doing it yourself and the concept of
reflection will be clearer.
(A) What are different types of JIT?
JIT compiler is a part of the runtime execution environment.
In Microsoft .NET there are three types of JIT compilers:
• Pre-JIT: - Pre-JIT compiles complete source code into native code in a single
compilation cycle. This is done at the time of deployment of the application.
• Econo-JIT: - Econo-JIT compiles only those methods that are called at runtime.
However, these compiled methods are removed when they are not required.
• Normal-JIT: - Normal-JIT compiles only those methods that are called at runtime.
These methods are compiled the first time they are called, and then they are stored in
cache. When the same methods are called again, the compiled code from cache is used
for execution.
(B) What are Value types and Reference types?
Value types directly contain their data that are either allocated on the stack or allocated in-line in
a structure. So value types are actual data.
Reference types store a reference to the value's memory address, and are allocated on the heap.
Reference types can be self-describing types, pointer types, or interface types. You can view
reference type as pointers to actual data.
Variables that are value types each have their own copy of the data, and therefore operations on
one variable do not affect other variables. Variables that are reference types can refer to the same
object; therefore, operations on one variable can affect the same object referred to by another
variable. All types derive from the System. Object base type.
(B) What is concept of Boxing and Unboxing ?
Boxing and unboxing act like bridges between value type and reference types. When we convert
value type to a reference type it’s termed as boxing. Unboxing is just vice-versa. When an object
box is cast back to its original value type, the value is copied out of the box and into the
appropriate storage location.
Below is sample code of boxing and unboxing where integer data type are converted in to object
and then vice versa.
int i = 1;
object obj = i; // boxing
int j = (int) obj; // unboxing
(B) What is the difference between VB.NET and C#?
Well this is the most debatable issue in .NET community and people treat languages like religion.
It is a subjective matter which language is best. Some like VB.NET’s natural style and some like
professional and terse C# syntaxes. Both use the same framework and speed is very much
equivalents. Still let us list down some major differences between them:-
Advantages VB.NET:-
• Has support for optional parameters that makes COM interoperability much easy.
• With Option Strict off late binding is supported.Legacy VB functionalities can be
used by using Microsoft.VisualBasic namespace.
• Has the WITH construct which is not in C#.
• The VB.NET parts of Visual Studio .NET compiles your code in the background.
While this is considered an advantage for small projects, people creating very
large projects have found that the IDE slows down considerably as the project
gets larger.
Advantages of C#
• XML documentation is generated from source code but this is now been
incorporated in Whidbey.
• Operator overloading which is not in current VB.NET but is been introduced in
Whidbey.
• Use of this statement makes unmanaged resource disposal simple.
• Access to Unsafe code. This allows pointer arithmetic etc, and can improve
performance in some situations. However, it is not to be used lightly, as a lot of
the normal safety of C# is lost (as the name implies).This is the major difference
that you can access unmanaged code in C# and not in VB.NET.
(I) what is the difference between System exceptions and Application
exceptions?
All exception derives from Exception Base class. Exceptions can be generated programmatically
or can be generated by system. Application Exception serves as the base class for all applicationspecific
exception classes. It derives from Exception but does not provide any extended
functionality. You should derive your custom application exceptions from Application Exception.
Application exception is used when we want to define user-defined exception, while system
exception is all that is defined by .
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