Common Language Runtime


1.1.   CLI or Common Language Infrastructure

The main purpose of CLI is to ensure the language neutral platform for application development and execution, including functions for Exception handling, Garbage Collection, security and interoperability. This is a standardized environment for the execution of the programs written in a wide range of high-level languages including Visual Basic, C#, and of course C++.
The CLI is essentially a specification for a virtual machine environment that enables applications written in diverse high - level programming languages to be executed in different system environments without the original source code ’ s being changed or replicated. The CLI specifies a standard intermediate language for the virtual machine to which the high - level language source code is compiled. With the .NET Framework, this intermediate language is referred to as Microsoft Intermediate Language (MSIL). Code in the intermediate language is ultimately mapped to machine code by a just - in - time (JIT) compiler when you execute a program. Of course, code in the CLI intermediate language can be executed within any other environment that has a CLI implementation. The CLI also defines a common set of data types called the Common Type System (CTS) that should be used for programs written in any programming language targeting a CLI implementation.

The CTS specifies how data types are used within the CLR and includes a set of predefined types. You may also define your own data types, and these must be defined in a particular way to be consistent with the CLR, as you’ll see. Having a standardized type system for representing data allows components written in different programming languages to handle data in a uniform way and makes it possible to integrate components written in different languages into a single application. Data security and program reliability is greatly enhanced by the CLR, in part because dynamic memory allocation and release for data is fully automatic, but also because the MSIL code for a program is comprehensively checked and validated before the program executes. The CLR is just one implementation of the CLI specification that executes under Microsoft Windows on a PC; there will undoubtedly be other implementations of the CLI for other operating system environments and hardware platforms. You’ll sometimes find that the terms CLI and CLR are used interchangeably, although it should be evident that they are not the same thing. The CLI is a standard specification; the CLR is Microsoft’s implementation of the CLI.
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