.Net Framework Interview Questions 9

By | May 13, 2014

How do I change the permission set for a code group? Use caspol. If you are the machine administrator, you can operate at the ‘machine’ level – which means not only that the changes you make become the default for the machine, but also that users cannot change the permissions to be more permissive. If you are a normal (non-admin) user you can still modify the permissions, but only to make them more restrictive. For example, to allow intranet code to do what it likes you might do this: caspol -cg 1.2 FullTrust Note that because this is more permissive than the default policy (on a standard system), you should only do this at the machine level – doing it at the user level will have no effect.

I can’t be bothered with all this CAS stuff. Can I turn it off? Yes, as long as you are an administrator. Just run: caspol -s off

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 VBScript, VB6 and C/C++. Value types are not instantiated using new go 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

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