C Sharp (programming language)
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C# (pronounced ) is a general-purpose,
high-level High-level and low-level, as technical terms, are used to classify, describe and point to specific goals of a systematic operation; and are applied in a wide range of contexts, such as, for instance, in domains as widely varied as computer scienc ...
multi-paradigm programming language Programming paradigms are a way to classify programming languages based on their features. Languages can be classified into multiple paradigms. Some paradigms are concerned mainly with implications for the execution model of the language, suc ...
. C# encompasses static typing, strong typing,
lexically scoped In computer programming, the scope of a name binding (an association of a name to an entity, such as a variable) is the part of a program where the name binding is valid; that is, where the name can be used to refer to the entity. In other parts ...
, imperative, declarative, functional,
generic Generic or generics may refer to: In business * Generic term, a common name used for a range or class of similar things not protected by trademark * Generic brand, a brand for a product that does not have an associated brand or trademark, other ...
,
object-oriented Object-oriented programming (OOP) is a programming paradigm based on the concept of " objects", which can contain data and code. The data is in the form of fields (often known as attributes or ''properties''), and the code is in the form of p ...
(
class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an analytical concept used differentl ...
-based), and component-oriented programming disciplines. The C# programming language was designed by
Anders Hejlsberg Anders Hejlsberg (, born 2 December 1960) is a Danish software engineer who co-designed several programming languages and development tools. He was the original author of Turbo Pascal and the chief architect of Delphi. He currently works for Mic ...
from
Microsoft Microsoft Corporation is an American multinational technology corporation producing computer software, consumer electronics, personal computers, and related services headquartered at the Microsoft Redmond campus located in Redmond, Washing ...
in 2000 and was later approved as an international standard by Ecma (ECMA-334) in 2002 and
ISO ISO is the most common abbreviation for the International Organization for Standardization. ISO or Iso may also refer to: Business and finance * Iso (supermarket), a chain of Danish supermarkets incorporated into the SuperBest chain in 2007 * Iso ...
/
IEC The International Electrotechnical Commission (IEC; in French: ''Commission électrotechnique internationale'') is an international standards organization that prepares and publishes international standards for all electrical, electronic and r ...
(ISO/IEC 23270) in 2003. Microsoft introduced C# along with
.NET Framework The .NET Framework (pronounced as "''dot net"'') is a proprietary software framework developed by Microsoft that runs primarily on Microsoft Windows. It was the predominant implementation of the Common Language Infrastructure (CLI) until bein ...
and
Visual Studio Visual Studio is an integrated development environment (IDE) from Microsoft. It is used to develop computer programs including web site, websites, web apps, web services and mobile apps. Visual Studio uses Microsoft software development platfor ...
, both of which were
closed-source Proprietary software is software that is deemed within the free and open-source software to be non-free because its creator, publisher, or other rightsholder or rightsholder partner exercises a legal monopoly afforded by modern copyright and inte ...
. At the time, Microsoft had no open-source products. Four years later, in 2004, a free and open-source project called
Mono Mono may refer to: Common meanings * Infectious mononucleosis, "the kissing disease" * Monaural, monophonic sound reproduction, often shortened to mono * Mono-, a numerical prefix representing anything single Music Performers * Mono (Japanese b ...
began, providing a
cross-platform In computing, cross-platform software (also called multi-platform software, platform-agnostic software, or platform-independent software) is computer software that is designed to work in several computing platforms. Some cross-platform software r ...
compiler In computing, a compiler is a computer program that translates computer code written in one programming language (the ''source'' language) into another language (the ''target'' language). The name "compiler" is primarily used for programs that ...
and
runtime environment In computer programming, a runtime system or runtime environment is a sub-system that exists both in the computer where a program is created, as well as in the computers where the program is intended to be run. The name comes from the compile t ...
for the C# programming language. A decade later, Microsoft released
Visual Studio Code Visual Studio Code, also commonly referred to as VS Code, is a source-code editor made by Microsoft with the Electron Framework, for Windows, Linux and macOS. Features include support for debugging, syntax highlighting, intelligent code comple ...
(code editor), Roslyn (compiler), and the unified .NET platform (software framework), all of which support C# and are free, open-source, and cross-platform. Mono also joined Microsoft but was not merged into .NET. the most recent stable version of the language is C# 11.0, which was released in 2022 in .NET 7.0.


Design goals

The Ecma standard lists these design goals for C#: * The language is intended to be a simple, modern, general-purpose,
object-oriented programming Object-oriented programming (OOP) is a programming paradigm based on the concept of "objects", which can contain data and code. The data is in the form of fields (often known as attributes or ''properties''), and the code is in the form of pr ...
language. * The language, and implementations thereof, should provide support for software engineering principles such as strong type checking, array
bounds checking In computer programming, bounds checking is any method of detecting whether a variable is within some bounds before it is used. It is usually used to ensure that a number fits into a given type (range checking), or that a variable being used as ...
, detection of attempts to use
uninitialized variable In computing, an uninitialized variable is a variable that is declared but is not set to a definite known value before it is used. It will have ''some'' value, but not a predictable one. As such, it is a programming error and a common source of b ...
s, and automatic
garbage collection Waste collection is a part of the process of waste management. It is the transfer of solid waste from the point of use and disposal to the point of treatment or landfill. Waste collection also includes the curbside collection of recyclabl ...
. Software robustness, durability, and programmer productivity are important. * The language is intended for use in developing
software components Component-based software engineering (CBSE), also called component-based development (CBD), is a branch of software engineering that emphasizes the separation of concerns with respect to the wide-ranging functionality available throughout a give ...
suitable for
deployment Deployment may refer to: Engineering and software Concepts * Blue-green deployment, a method of installing changes to a web, app, or database server by swapping alternating production and staging servers * Continuous deployment, a software e ...
in distributed environments. * Portability is very important for
source code In computing, source code, or simply code, is any collection of code, with or without comments, written using a human-readable programming language, usually as plain text. The source code of a program is specially designed to facilitate the wo ...
and programmers, especially those already familiar with C and
C++ C++ (pronounced "C plus plus") is a high-level general-purpose programming language created by Danish computer scientist Bjarne Stroustrup as an extension of the C programming language, or "C with Classes". The language has expanded significan ...
. * Support for
internationalization In economics, internationalization or internationalisation is the process of increasing involvement of enterprises in international markets, although there is no agreed definition of internationalization. Internationalization is a crucial strateg ...
is very important. * C# is intended to be suitable for writing applications for both hosted and
embedded system An embedded system is a computer system—a combination of a computer processor, computer memory, and input/output peripheral devices—that has a dedicated function within a larger mechanical or electronic system. It is ''embedded'' as ...
s, ranging from the very large that use sophisticated
operating system An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs. Time-sharing operating systems schedule tasks for efficient use of the system and may also in ...
s, down to the very small having dedicated functions. * Although C# applications are intended to be economical with regard to memory and
processing power In computing, computer performance is the amount of useful work accomplished by a computer system. Outside of specific contexts, computer performance is estimated in terms of accuracy, efficiency and speed of executing computer program instruction ...
requirements, the language was not intended to compete directly on performance and size with C or assembly language.


History

During the development of the
.NET Framework The .NET Framework (pronounced as "''dot net"'') is a proprietary software framework developed by Microsoft that runs primarily on Microsoft Windows. It was the predominant implementation of the Common Language Infrastructure (CLI) until bein ...
, the class libraries were originally written using a
managed code Managed code is computer program code that requires and will execute only under the management of a Common Language Infrastructure (CLI); Virtual Execution System (VES); virtual machine, e.g. .NET, CoreFX, or .NET Framework; Common Language Runt ...
compiler system called ''" Simple Managed C"'' (SMC). In January 1999,
Anders Hejlsberg Anders Hejlsberg (, born 2 December 1960) is a Danish software engineer who co-designed several programming languages and development tools. He was the original author of Turbo Pascal and the chief architect of Delphi. He currently works for Mic ...
formed a team to build a new language at the time called Cool, which stood for " C-like Object Oriented Language". Microsoft had considered keeping the name "Cool" as the final name of the language, but chose not to do so for trademark reasons. By the time the .NET project was publicly announced at the July 2000
Professional Developers Conference Microsoft's Professional Developers Conference (PDC) was a series of conferences for software developers; the conference was held infrequently to coincide with beta releases of the Windows operating system, and showcased topics of interest to tho ...
, the language had been renamed C#, and the class libraries and
ASP.NET ASP.NET is an open-source, server-side web-application framework designed for web development to produce dynamic web pages. It was developed by Microsoft to allow programmers to build dynamic web sites, applications and services. The name s ...
runtime had been ported to C#. Hejlsberg is C#'s principal designer and lead architect at Microsoft, and was previously involved with the design of
Turbo Pascal Turbo Pascal is a software development system that includes a compiler and an integrated development environment (IDE) for the Pascal programming language running on CP/M, CP/M-86, and DOS. It was originally developed by Anders Hejlsberg at ...
,
Embarcadero Delphi Delphi is a general-purpose programming language and a software product that uses the Delphi dialect of the Object Pascal programming language and provides an integrated development environment (IDE) for rapid application development of desktop, ...
(formerly CodeGear Delphi, Inprise Delphi and Borland Delphi), and
Visual J++ Visual J++ is Microsoft's discontinued implementation of Java. Syntax, keywords, and grammatical conventions were the same as Java's. It was introduced in 1996 and discontinued in January 2004, replaced to a certain extent by J# and C#. The i ...
. In interviews and technical papers he has stated that flaws in most major programming languages (e.g.
C++ C++ (pronounced "C plus plus") is a high-level general-purpose programming language created by Danish computer scientist Bjarne Stroustrup as an extension of the C programming language, or "C with Classes". The language has expanded significan ...
,
Java Java (; id, Jawa, ; jv, ꦗꦮ; su, ) is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea to the north. With a population of 151.6 million people, Java is the world's List ...
,
Delphi Delphi (; ), in legend previously called Pytho (Πυθώ), in ancient times was a sacred precinct that served as the seat of Pythia, the major oracle who was consulted about important decisions throughout the ancient classical world. The oracle ...
, and Smalltalk) drove the fundamentals of the Common Language Runtime (CLR), which, in turn, drove the design of the C# language itself.
James Gosling James Gosling (born May 19, 1955) is a Canadian computer scientist, best known as the founder and lead designer behind the Java programming language. Gosling was elected a member of the National Academy of Engineering in 2004 for the conception ...
, who created the
Java Java (; id, Jawa, ; jv, ꦗꦮ; su, ) is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea to the north. With a population of 151.6 million people, Java is the world's List ...
programming language in 1994, and
Bill Joy William Nelson Joy (born November 8, 1954) is an American computer engineer and venture capitalist. He co-founded Sun Microsystems in 1982 along with Scott McNealy, Vinod Khosla, and Andy Bechtolsheim, and served as Chief Scientist and CTO at ...
, a co-founder of
Sun Microsystems Sun Microsystems, Inc. (Sun for short) was an American technology company that sold computers, computer components, software, and information technology services and created the Java programming language, the Solaris operating system, ZFS, the ...
, the originator of Java, called C# an "imitation" of Java; Gosling further said that " # issort of Java with reliability, productivity and security deleted." Klaus Kreft and Angelika Langer (authors of a C++ streams book) stated in a blog post that "Java and C# are almost identical programming languages. Boring repetition that lacks innovation," "Hardly anybody will claim that Java or C# are revolutionary programming languages that changed the way we write programs," and "C# borrowed a lot from Java - and vice versa. Now that C# supports
boxing Boxing (also known as "Western boxing" or "pugilism") is a combat sport in which two people, usually wearing protective gloves and other protective equipment such as hand wraps and mouthguards, throw punches at each other for a predetermine ...
and unboxing, we'll have a very similar feature in Java." In July 2000, Hejlsberg said that C# is "not a Java clone" and is "much closer to C++" in its design. Since the release of C# 2.0 in November 2005, the C# and Java languages have evolved on increasingly divergent trajectories, becoming two quite different languages. One of the first major departures came with the addition of generics to both languages, with vastly different implementations. C# makes use of reification to provide "first-class" generic objects that can be used like any other class, with code generation performed at class-load time. Furthermore, C# has added several major features to accommodate functional-style programming, culminating in the
LINQ Language Integrated Query (LINQ, pronounced "link") is a Microsoft .NET Framework component that adds native data querying capabilities to .NET languages, originally released as a major part of .NET Framework 3.5 in 2007. LINQ extends the langu ...
extensions released with C# 3.0 and its supporting framework of
lambda expressions Lambda expression may refer to: *Lambda expression in computer programming, also called an anonymous function, is a defined function not bound to an identifier. * Lambda expression in lambda calculus, a formal system in mathematical logic and ...
,
extension method In object-oriented computer programming, an extension method is a method added to an object after the original object was compiled. The modified object is often a class, a prototype or a type. Extension methods are features of some object-orie ...
s, and
anonymous type Anonymous types are a feature of C# 3.0, Visual Basic .NET 9.0, Oxygene, Scala and Go that allows data types to encapsulate a set of properties into a single object without having to first explicitly define a type. This is an important feature ...
s. These features enable C# programmers to use functional programming techniques, such as closures, when it is advantageous to their application. The LINQ extensions and the functional imports help developers reduce the amount of boilerplate code that is included in common tasks like querying a database, parsing an xml file, or searching through a data structure, shifting the emphasis onto the actual program logic to help improve readability and maintainability. C# used to have a
mascot A mascot is any human, animal, or object thought to bring luck, or anything used to represent a group with a common public identity, such as a school, professional sports team, society, military unit, or brand name. Mascots are also used as fi ...
called Andy (named after Anders Hejlsberg). It was retired on January 29, 2004. C# was originally submitted to the ISO/IEC JTC 1 subcommittee SC 22 for review, under ISO/IEC 23270:2003, was withdrawn and was then approved under ISO/IEC 23270:2006. The 23270:2006 is withdrawn under 23270:2018 and approved with this version.


Name

Microsoft first used the name C# in 1988 for a variant of the C language designed for incremental compilation. That project was not completed, and the name was later reused. The name "C sharp" was inspired by the musical notation whereby a sharp symbol indicates that the written note should be made a
semitone A semitone, also called a half step or a half tone, is the smallest musical interval commonly used in Western tonal music, and it is considered the most dissonant when sounded harmonically. It is defined as the interval between two adjacent no ...
higher in pitch. This is similar to the language name of
C++ C++ (pronounced "C plus plus") is a high-level general-purpose programming language created by Danish computer scientist Bjarne Stroustrup as an extension of the C programming language, or "C with Classes". The language has expanded significan ...
, where "++" indicates that a variable should be incremented by 1 after being evaluated. The sharp symbol also resembles a
ligature Ligature may refer to: * Ligature (medicine), a piece of suture used to shut off a blood vessel or other anatomical structure ** Ligature (orthodontic), used in dentistry * Ligature (music), an element of musical notation used especially in the me ...
of four "+" symbols (in a two-by-two grid), further implying that the language is an increment of C++. Due to technical limitations of display (standard fonts, browsers, etc.) and the fact that the sharp symbol () is not present on most
keyboard layout A keyboard layout is any specific physical, visual or functional arrangement of the keys, legends, or key-meaning associations (respectively) of a computer keyboard, mobile phone, or other computer-controlled typographic keyboard. is the actua ...
s, the
number sign The symbol is known variously in English-speaking regions as the number sign, hash, or pound sign. The symbol has historically been used for a wide range of purposes including the designation of an ordinal number and as a Typographic ligature, ...
() was chosen to approximate the sharp symbol in the written name of the programming language. This convention is reflected in the ECMA-334 C# Language Specification. The "sharp" suffix has been used by a number of other .NET languages that are variants of existing languages, including J# (a .NET language also designed by Microsoft that is derived from Java 1.1), A# (from
Ada Ada may refer to: Places Africa * Ada Foah, a town in Ghana * Ada (Ghana parliament constituency) * Ada, Osun, a town in Nigeria Asia * Ada, Urmia, a village in West Azerbaijan Province, Iran * Ada, Karaman, a village in Karaman Province, ...
), and the
functional programming In computer science, functional programming is a programming paradigm where programs are constructed by applying and composing functions. It is a declarative programming paradigm in which function definitions are trees of expressions that ...
language F#. The original implementation of Eiffel for .NET was called Eiffel#, a name retired since the full
Eiffel Eiffel may refer to: Places * Eiffel Peak, a summit in Alberta, Canada * Champ de Mars – Tour Eiffel station, Paris, France; a transit station Structures * Eiffel Tower, in Paris, France, designed by Gustave Eiffel * Eiffel Bridge, Ungheni, M ...
language is now supported. The suffix has also been used for
libraries A library is a collection of Document, materials, books or media that are accessible for use and not just for display purposes. A library provides physical (hard copies) or electronic media, digital access (soft copies) materials, and may be a ...
, such as Gtk# (a .NET wrapper for
GTK GTK (formerly GIMP ToolKit and GTK+) is a free and open-source cross-platform widget toolkit for creating graphical user interfaces (GUIs). It is licensed under the terms of the GNU Lesser General Public License, allowing both free and propriet ...
and other GNOME libraries) and Cocoa# (a wrapper for
Cocoa Cocoa may refer to: Chocolate * Chocolate * ''Theobroma cacao'', the cocoa tree * Cocoa bean, seed of ''Theobroma cacao'' * Chocolate liquor, or cocoa liquor, pure, liquid chocolate extracted from the cocoa bean, including both cocoa butter and ...
).


Versions


Syntax

The core syntax of the C# language is similar to that of other C-style languages such as C, C++ and Java, particularly: * Semicolons are used to denote the end of a statement. *
Curly brackets A bracket is either of two tall fore- or back-facing punctuation marks commonly used to isolate a segment of text or data from its surroundings. Typically deployed in symmetric pairs, an individual bracket may be identified as a 'left' or 'r ...
are used to group statements. Statements are commonly grouped into methods (functions), methods into classes, and classes into
namespaces In computing, a namespace is a set of signs (''names'') that are used to identify and refer to objects of various kinds. A namespace ensures that all of a given set of objects have unique names so that they can be easily identified. Namespaces ...
. * Variables are assigned using an
equals sign The equals sign (British English, Unicode) or equal sign (American English), also known as the equality sign, is the mathematical symbol , which is used to indicate equality in some well-defined sense. In an equation, it is placed between two ...
, but compared using two consecutive equals signs. *
Square brackets A bracket is either of two tall fore- or back-facing punctuation marks commonly used to isolate a segment of text or data from its surroundings. Typically deployed in symmetric pairs, an individual bracket may be identified as a 'left' or 'r ...
are used with
arrays An array is a systematic arrangement of similar objects, usually in rows and columns. Things called an array include: {{TOC right Music * In twelve-tone and serial composition, the presentation of simultaneous twelve-tone sets such that the ...
, both to declare them and to get a value at a given index in one of them.


Distinguishing features

Some notable features of C# that distinguish it from C, C++, and Java where noted, are:


Portability

By design, C# is the programming language that most directly reflects the underlying Common Language Infrastructure (CLI). Most of its intrinsic types correspond to value-types implemented by the CLI framework. However, the language specification does not state the code generation requirements of the compiler: that is, it does not state that a C# compiler must target a Common Language Runtime, or generate
Common Intermediate Language Common Intermediate Language (CIL), formerly called Microsoft Intermediate Language (MSIL) or Intermediate Language (IL), is the intermediate language binary instruction set defined within the Common Language Infrastructure (CLI) specification. ...
(CIL), or generate any other specific format. Theoretically, a C# compiler could generate machine code like traditional compilers of C++ or Fortran.


Typing

C# supports strongly, implicitly typed variable declarations with the keyword var, and implicitly typed arrays with the keyword new[] followed by a collection initializer. C# supports a strict Boolean data type, bool. Statements that take conditions, such as while and if, require an expression of a type that implements the true operator, such as the Boolean type. While C++ also has a Boolean type, it can be freely converted to and from integers, and expressions such as if (a) require only that a is convertible to bool, allowing a to be an int, or a pointer. C# disallows this "integer meaning true or false" approach, on the grounds that forcing programmers to use expressions that return exactly bool can prevent certain types of programming mistakes such as if (a = b) (use of assignment = instead of equality

). C# is more
type safe In computer science, type safety and type soundness are the extent to which a programming language discourages or prevents type errors. Type safety is sometimes alternatively considered to be a property of facilities of a computer language; that is ...
than C++. The only
implicit conversion In computer science, type conversion, type casting, type coercion, and type juggling are different ways of changing an expression from one data type to another. An example would be the conversion of an integer value into a floating point valu ...
s by default are those that are considered safe, such as widening of integers. This is enforced at compile-time, during
JIT Jit (also known as jiti, jit-jive and the Harare beat) is a style of popular Zimbabwean dance music. It features a swift rhythm played on drums and accompanied by a guitar. Jit evolved out many diverse influences, including domestic chimurenga, ...
, and, in some cases, at runtime. No implicit conversions occur between Booleans and integers, nor between enumeration members and integers (except for literal 0, which can be implicitly converted to any enumerated type). Any user-defined conversion must be explicitly marked as explicit or implicit, unlike C++
copy constructor In class-based, object-oriented programming, a constructor (abbreviation: ctor) is a special type of subroutine called to create an object. It prepares the new object for use, often accepting arguments that the constructor uses to set required ...
s and conversion operators, which are both implicit by default. C# has explicit support for covariance and contravariance in generic types, unlike C++ which has some degree of support for contravariance simply through the semantics of return types on virtual methods.
Enumeration An enumeration is a complete, ordered listing of all the items in a collection. The term is commonly used in mathematics and computer science to refer to a listing of all of the elements of a set. The precise requirements for an enumeration (fo ...
members are placed in their own
scope Scope or scopes may refer to: People with the surname * Jamie Scope (born 1986), English footballer * John T. Scopes (1900–1970), central figure in the Scopes Trial regarding the teaching of evolution Arts, media, and entertainment * Cinem ...
. The C# language does not allow for global variables or functions. All methods and members must be declared within classes. Static members of public classes can substitute for global variables and functions. Local variables cannot
shadow A shadow is a dark area where light from a light source is blocked by an opaque object. It occupies all of the three-dimensional volume behind an object with light in front of it. The cross section of a shadow is a two-dimensional silhouette, ...
variables of the enclosing block, unlike C and C++.


Metaprogramming

Metaprogramming Metaprogramming is a programming technique in which computer programs have the ability to treat other programs as their data. It means that a program can be designed to read, generate, analyze or transform other programs, and even modify itself ...
can be achieved in several ways: *
Reflection Reflection or reflexion may refer to: Science and technology * Reflection (physics), a common wave phenomenon ** Specular reflection, reflection from a smooth surface *** Mirror image, a reflection in a mirror or in water ** Signal reflection, in ...
is supported through .NET APIs, which enable scenarios such as type metadata inspection and dynamic method invocation. * Expression trees represent code as an
abstract syntax tree In computer science, an abstract syntax tree (AST), or just syntax tree, is a tree representation of the abstract syntactic structure of text (often source code) written in a formal language. Each node of the tree denotes a construct occurr ...
, where each node is an expression that can be inspected or executed. This enables dynamic modification of executable code at runtime. Expression trees introduce some
homoiconicity In computer programming, homoiconicity (from the Greek words ''homo-'' meaning "the same" and ''icon'' meaning "representation") is a property of some programming languages. A language is homoiconic if a program written in it can be manipulated as ...
to the language. *
Attributes Attribute may refer to: * Attribute (philosophy), an extrinsic property of an object * Attribute (research), a characteristic of an object * Grammatical modifier, in natural languages * Attribute (computing), a specification that defines a prope ...
are
metadata Metadata is "data that provides information about other data", but not the content of the data, such as the text of a message or the image itself. There are many distinct types of metadata, including: * Descriptive metadata – the descriptive ...
that can be attached to types, members, or entire assemblies, equivalent to annotations in Java. Attributes are accessible both to the compiler and to code through reflection. Many of these attributes duplicate the functionality of GCC's and VisualC++'s platform-dependent preprocessor directives. * The .NET Compiler Platform (Roslyn) provides API access to language compilation services, allowing for the compilation of C# code from within .NET applications. It exposes APIs for syntactic (
lexical Lexical may refer to: Linguistics * Lexical corpus or lexis, a complete set of all words in a language * Lexical item, a basic unit of lexicographical classification * Lexicon, the vocabulary of a person, language, or branch of knowledge * Lex ...
) analysis of code, semantic analysis, dynamic compilation to CIL, and code emission. * Source generators, a feature of the Roslyn C# compiler, enable compile time metaprogramming. During the compilation process, developers can inspect the code being compiled with the compiler's API and pass additional generated C# source code to be compiled.


Methods and functions

A method in C# is a member of a class that can be invoked as a function (a sequence of instructions), rather than the mere value-holding capability of a class property. As in other syntactically similar languages, such as C++ and
ANSI C ANSI C, ISO C, and Standard C are successive standards for the C programming language published by the American National Standards Institute (ANSI) and ISO/IEC JTC 1/SC 22/WG 14 of the International Organization for Standardization (ISO) and th ...
, the signature of a method is a declaration comprising in order: any optional accessibility keywords (such as private), the explicit specification of its return type (such as int, or the keyword void if no value is returned), the name of the method, and finally, a parenthesized sequence of comma-separated parameter specifications, each consisting of a parameter's type, its formal name and optionally, a default value to be used whenever none is provided. Certain specific kinds of methods, such as those that simply get or set a class property by return value or assignment, do not require a full signature, but in the general case, the definition of a class includes the full signature declaration of its methods. Like C++, and unlike Java, C# programmers must use the scope modifier keyword virtual to allow methods to be overridden by subclasses. ''Extension methods'' in C# allow programmers to use static methods as if they were methods from a class's method table, allowing programmers to add methods to an object that they feel should exist on that object and its derivatives. The type dynamic allows for run-time method binding, allowing for JavaScript-like method calls and run-time
object composition In computer science, object composition and object aggregation are closely related ways to combine objects or data types into more complex ones. In conversation the distinction between composition and aggregation is often ignored. Common kind ...
. C# has support for strongly-typed
function pointer A function pointer, also called a subroutine pointer or procedure pointer, is a pointer that points to a function. As opposed to referencing a data value, a function pointer points to executable code within memory. Dereferencing the function poi ...
s via the keyword delegate. Like the Qt framework's pseudo-C++ ''signal'' and ''slot'', C# has semantics specifically surrounding publish-subscribe style events, though C# uses delegates to do so. C# offers Java-like synchronized method calls, via the attribute ethodImpl(MethodImplOptions.Synchronized)/code>, and has support for mutually-exclusive locks via the keyword lock.


Property

C# supports classes with
properties Property is the ownership of land, resources, improvements or other tangible objects, or intellectual property. Property may also refer to: Mathematics * Property (mathematics) Philosophy and science * Property (philosophy), in philosophy an ...
. The properties can be simple accessor functions with a backing field, or implement getter and setter functions. Since C# 3.0 the
syntactic sugar In computer science, syntactic sugar is syntax within a programming language that is designed to make things easier to read or to express. It makes the language "sweeter" for human use: things can be expressed more clearly, more concisely, or in an ...
of auto-implemented properties is available, where the accessor (getter) and mutator (setter) encapsulate operations on a single
attribute Attribute may refer to: * Attribute (philosophy), an extrinsic property of an object * Attribute (research), a characteristic of an object * Grammatical modifier, in natural languages * Attribute (computing), a specification that defines a prope ...
of a class.


Namespace

A C# namespace provides the same level of code isolation as a Java package or a C++ , with very similar rules and features to a package. Namespaces can be imported with the "using" syntax.


Memory access

In C#, memory address pointers can only be used within blocks specifically marked as ''unsafe'', and programs with unsafe code need appropriate permissions to run. Most object access is done through safe object references, which always either point to a "live" object or have the well-defined
null Null may refer to: Science, technology, and mathematics Computing * Null (SQL) (or NULL), a special marker and keyword in SQL indicating that something has no value * Null character, the zero-valued ASCII character, also designated by , often use ...
value; it is impossible to obtain a reference to a "dead" object (one that has been garbage collected), or to a random block of memory. An unsafe pointer can point to an instance of an 'unmanaged' value type that does not contain any references to garbage-collected objects, array, string, or a block of stack-allocated memory. Code that is not marked as unsafe can still store and manipulate pointers through the System.IntPtr type, but it cannot dereference them. Managed memory cannot be explicitly freed; instead, it is automatically garbage collected. Garbage collection addresses the problem of
memory leak In computer science, a memory leak is a type of resource leak that occurs when a computer program incorrectly manages memory allocations in a way that memory which is no longer needed is not released. A memory leak may also happen when an object ...
s by freeing the programmer of responsibility for releasing memory that is no longer needed in most cases. Code that retains references to objects longer than is required can still experience higher memory usage than necessary, however once the final reference to an object is released the memory is available for garbage collection.


Exception

A range of standard exceptions are available to programmers. Methods in standard libraries regularly throw system exceptions in some circumstances and the range of exceptions thrown is normally documented. Custom exception classes can be defined for classes allowing handling to be put in place for particular circumstances as needed.
Checked exceptions In computing and computer programming, exception handling is the process of responding to the occurrence of ''exceptions'' – anomalous or exceptional conditions requiring special processing – during the execution of a program. In general, an ...
are not present in C# (in contrast to Java). This has been a conscious decision based on the issues of scalability and versionability.


Polymorphism

Unlike
C++ C++ (pronounced "C plus plus") is a high-level general-purpose programming language created by Danish computer scientist Bjarne Stroustrup as an extension of the C programming language, or "C with Classes". The language has expanded significan ...
, C# does not support
multiple inheritance Multiple inheritance is a feature of some object-oriented computer programming languages in which an object or class can inherit features from more than one parent object or parent class. It is distinct from single inheritance, where an object or ...
, although a class can implement any number of " interfaces" (fully abstract classes). This was a design decision by the language's lead architect to avoid complications and to simplify architectural requirements throughout CLI. When implementing multiple interfaces that contain a method with the same name and taking parameters of the same type in the same order (i.e. the same
signature A signature (; from la, signare, "to sign") is a handwritten (and often stylized) depiction of someone's name, nickname, or even a simple "X" or other mark that a person writes on documents as a proof of identity and intent. The writer of a ...
), similar to
Java Java (; id, Jawa, ; jv, ꦗꦮ; su, ) is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea to the north. With a population of 151.6 million people, Java is the world's List ...
, C# allows both a single method to cover all interfaces and if necessary specific methods for each interface. However, unlike Java, C# supports
operator overloading In computer programming, operator overloading, sometimes termed ''operator ad hoc polymorphism'', is a specific case of polymorphism, where different operators have different implementations depending on their arguments. Operator overloading i ...
.


Language Integrated Query (LINQ)

C# has the ability to utilize
LINQ Language Integrated Query (LINQ, pronounced "link") is a Microsoft .NET Framework component that adds native data querying capabilities to .NET languages, originally released as a major part of .NET Framework 3.5 in 2007. LINQ extends the langu ...
through the .NET Framework. A developer can query a variety of data sources, provided IEnumerable<T> interface is implemented on the object. This includes XML documents, an ADO.NET dataset, and SQL databases. Using LINQ in C# brings advantages like
Intellisense Intelligent code completion is a context-aware code completion feature in some programming environments that speeds up the process of coding applications by reducing typos and other common mistakes. Attempts at this are usually done through auto- ...
support, strong filtering capabilities, type safety with compile error checking ability, and consistency for querying data over a variety of sources. There are several different language structures that can be utilized with C# and LINQ and they are query expressions, lambda expressions, anonymous types, implicitly typed variables, extension methods, and object initializers.


Functional programming

Though primarily an imperative language, C# 2.0 offered limited support for functional programming through
first-class functions In computer science, a programming language is said to have first-class functions if it treats functions as first-class citizens. This means the language supports passing functions as arguments to other functions, returning them as the values from ...
and closures in the form of anonymous delegates. C# 3.0 expanded support for functional programming with the introduction of a lightweight syntax for lambda expressions, extension methods (an affordance for modules), and a
list comprehension A list comprehension is a syntactic construct available in some programming languages for creating a list based on existing lists. It follows the form of the mathematical ''set-builder notation'' (''set comprehension'') as distinct from the use of ...
syntax in the form of a "query comprehension" language. C# 7.0 adds features typically found in functional languages like tuples, local functions and
pattern matching In computer science, pattern matching is the act of checking a given sequence of tokens for the presence of the constituents of some pattern. In contrast to pattern recognition, the match usually has to be exact: "either it will or will not be ...
. C# 9.0 introduces record feature which is primarily built for better supporting immutable data models.


Common type system

C# has a ''unified type system''. This unified type system is called
Common Type System In Microsoft's .NET Framework, the Common Type System (CTS) is a standard that specifies how type definitions and specific values of types are represented in computer memory. It is intended to allow programs written in different programming langu ...
(CTS). A unified type system implies that all types, including primitives such as integers, are subclasses of the class. For example, every type inherits a method.


Categories of data types

CTS separates data types into two categories: # Reference types # Value types Instances of value types neither have referential identity nor referential comparison semantics. Equality and inequality comparisons for value types compare the actual data values within the instances, unless the corresponding operators are overloaded. Value types are derived from , always have a default value, and can always be created and copied. Some other limitations on value types are that they cannot derive from each other (but can implement interfaces) and cannot have an explicit default (parameterless) constructor. Examples of value types are all primitive types, such as (a signed 32-bit integer), (a 32-bit IEEE floating-point number), (a 16-bit Unicode code unit), and (identifies a specific point in time with nanosecond precision). Other examples are (enumerations) and (user defined structures). In contrast, reference types have the notion of referential identity, meaning that each instance of a reference type is inherently distinct from every other instance, even if the data within both instances is the same. This is reflected in default equality and inequality comparisons for reference types, which test for referential rather than structural equality, unless the corresponding operators are overloaded (such as the case for ). Some operations are not always possible, such as creating an instance of a reference type, copying an existing instance, or performing a value comparison on two existing instances. Though specific reference types can provide such services by exposing a public constructor or implementing a corresponding interface (such as or ). Examples of reference types are (the ultimate base class for all other C# classes), (a string of Unicode characters), and (a base class for all C# arrays). Both type categories are extensible with user-defined types.


Boxing and unboxing

''Boxing'' is the operation of converting a value-type object into a value of a corresponding reference type. Boxing in C# is implicit. ''Unboxing'' is the operation of converting a value of a reference type (previously boxed) into a value of a value type. Unboxing in C# requires an explicit type cast. A boxed object of type T can only be unboxed to a T (or a nullable T). Example: int foo = 42; // Value type. object bar = foo; // foo is boxed to bar. int foo2 = (int)bar; // Unboxed back to value type.


Libraries

The C# specification details a minimum set of types and class libraries that the compiler expects to have available. In practice, C# is most often used with some implementation of the Common Language Infrastructure (CLI), which is standardized as ECMA-335 ''Common Language Infrastructure (CLI)''. In addition to the standard CLI specifications, there are many commercial and community class libraries that build on top of the .NET framework libraries to provide additional functionality. C# can make calls to any library included in the List of .NET libraries and frameworks.


Examples


Hello World

The following is a very simple C# program, a version of the classic "
Hello world ''Hello'' is a salutation or greeting in the English language. It is first attested in writing from 1826. Early uses ''Hello'', with that spelling, was used in publications in the U.S. as early as the 18 October 1826 edition of the '' Norwich ...
" example using the top-level statements feature introduced in C# 9: using System; Console.WriteLine("Hello, world!"); For code written as C# 8 or lower, the entry point logic of a program must be written in a Main method inside a type: using System; // A version of the classic "Hello World" program class Program This code will display this text in the console window: Hello, world! Each line has a purpose: using System; The above line imports all types in the System namespace. For example, the Console class used later in the source code is defined in the System namespace, meaning it can be used without supplying the full name of the type (which includes the namespace). // A version of the classic "Hello World" program This line is a comment; it describes and documents the code for the programmer(s). class Program Above is a
class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an analytical concept used differentl ...
definition for the class. Everything that follows between the pair of braces describes that class. The curly brackets demarcate the boundaries of a code block. In this first instance, they are marking the start and end of the class. static void Main() This declares the class member method where the program begins execution. The .NET runtime calls the method. Unlike in
Java Java (; id, Jawa, ; jv, ꦗꦮ; su, ) is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea to the north. With a population of 151.6 million people, Java is the world's List ...
, the method does not need the keyword, which tells the compiler that the method can be called from anywhere by any class. Writing is equivalent to writing . The static keyword makes the method accessible without an instance of . Each console application's entry point must be declared otherwise the program would require an instance of , but any instance would require a program. To avoid that irresolvable
circular dependency In software engineering, a circular dependency is a relation between two or more modules which either directly or indirectly depend on each other to function properly. Such modules are also known as mutually recursive. Overview Circular depend ...
, C# compilers processing
console application A console application is a computer program designed to be used via a text-only computer interface, such as a text terminal, the command-line interface of some operating systems (Unix, DOS, etc.) or the text-based interface included with most gr ...
s (like that above) report an error if there is no method. The keyword declares that has no
return value In computer programming, a return statement causes execution to leave the current subroutine and resume at the point in the code immediately after the instruction which called the subroutine, known as its return address. The return address is sa ...
. Console.WriteLine("Hello, world!"); This line writes the output. is a static class in the namespace. It provides an interface to the standard input, output, and error streams for console applications. The program calls the method , which displays on the console a line with the argument, the string .


GUI

A Windows
GUI The GUI ( "UI" by itself is still usually pronounced . or ), graphical user interface, is a form of user interface that allows users to interact with electronic devices through graphical icons and audio indicator such as primary notation, inste ...
example: using System; using System.Windows.Forms; class Program This example is similar to the previous example, except that it generates a
dialog box The dialog box (also called dialogue box (non-U.S. English), message box or simply dialog) is a graphical control element in the form of a small window that communicates information to the user and prompts them for a response. Dialog boxes ar ...
that contains the message "Hello, World!" instead of writing it to the console.


Images

Another useful library is the System.Drawing library, which is used to programmatically draw images. For example: using System; using System.Drawing; public class Example This will create an image that is identical to that stored in "Image.png".


Standardization and licensing

In August 2001,
Microsoft Microsoft Corporation is an American multinational technology corporation producing computer software, consumer electronics, personal computers, and related services headquartered at the Microsoft Redmond campus located in Redmond, Washing ...
, Hewlett-Packard and
Intel Intel Corporation is an American multinational corporation and technology company headquartered in Santa Clara, California. It is the world's largest semiconductor chip manufacturer by revenue, and is one of the developers of the x86 seri ...
co-sponsored the submission of specifications for C# as well as the Common Language Infrastructure (CLI) to the standards organization
Ecma International Ecma International () is a nonprofit standards organization for information and communication systems. It acquired its current name in 1994, when the European Computer Manufacturers Association (ECMA) changed its name to reflect the organization ...
. In December 2001, ECMA released ECMA-334 ''C# Language Specification''. C# became an
ISO ISO is the most common abbreviation for the International Organization for Standardization. ISO or Iso may also refer to: Business and finance * Iso (supermarket), a chain of Danish supermarkets incorporated into the SuperBest chain in 2007 * Iso ...
/
IEC The International Electrotechnical Commission (IEC; in French: ''Commission électrotechnique internationale'') is an international standards organization that prepares and publishes international standards for all electrical, electronic and r ...
standard in 2003 (ISO/IEC 23270:2003 - ''Information technology — Programming languages — C#''). ECMA had previously adopted equivalent specifications as the 2nd edition of C#, in December 2002. In June 2005, ECMA approved edition 3 of the C# specification, and updated ECMA-334. Additions included partial classes, anonymous methods, nullable types, and generics (somewhat similar to C++
templates Template may refer to: Tools * Die (manufacturing), used to cut or shape material * Mold, in a molding process * Stencil, a pattern or overlay used in graphic arts (drawing, painting, etc.) and sewing to replicate letters, shapes or designs Co ...
). In July 2005, ECMA submitted to ISO/IEC JTC 1/SC 22, via the latter's Fast-Track process, the standards and related TRs. This process usually takes 6–9 months. The C# language definition and the
CLI CLI may refer to: Computing * Call Level Interface, an SQL database management API * Command-line interface, of a computer program * Command-line interpreter or command language interpreter; see List of command-line interpreters * CLI (x86 instruc ...
are standardized under
ISO ISO is the most common abbreviation for the International Organization for Standardization. ISO or Iso may also refer to: Business and finance * Iso (supermarket), a chain of Danish supermarkets incorporated into the SuperBest chain in 2007 * Iso ...
/
IEC The International Electrotechnical Commission (IEC; in French: ''Commission électrotechnique internationale'') is an international standards organization that prepares and publishes international standards for all electrical, electronic and r ...
and Ecma standards that provide
reasonable and non-discriminatory licensing Reasonable and non-discriminatory (RAND) terms, also known as fair, reasonable, and non-discriminatory (FRAND) terms, denote a voluntary licensing commitment that standards organizations often request from the owner of an intellectual property r ...
protection from patent claims. Microsoft initially agreed not to sue open-source developers for violating patents in non-profit projects for the part of the framework that is covered by the OSP. Microsoft has also agreed not to enforce patents relating to
Novell Novell, Inc. was an American software and services company headquartered in Provo, Utah, that existed from 1980 until 2014. Its most significant product was the multi-platform network operating system known as Novell NetWare. Under the lead ...
products against Novell's paying customers with the exception of a list of products that do not explicitly mention C#, .NET or Novell's implementation of .NET ( The Mono Project). However, Novell maintained that Mono does not infringe any Microsoft patents. Microsoft also made a specific agreement not to enforce patent rights related to the Moonlight browser plugin, which depends on Mono, provided it is obtained through Novell. A decade later, Microsoft began developing free, open-source, and cross-platform tooling for C#, namely
Visual Studio Code Visual Studio Code, also commonly referred to as VS Code, is a source-code editor made by Microsoft with the Electron Framework, for Windows, Linux and macOS. Features include support for debugging, syntax highlighting, intelligent code comple ...
,
.NET Core The domain name net is a generic top-level domain (gTLD) used in the Domain Name System of the Internet. The name is derived from the word ''network'', indicating it was originally intended for organizations involved in networking technologies ...
, and Roslyn. Mono joined Microsoft as a project of
Xamarin Xamarin is a Microsoft-owned San Francisco-based software company founded in May 2011 by the engineers that created Mono, Xamarin.Android (formerly Mono for Android) and Xamarin.iOS (formerly MonoTouch), which are cross-platform implementatio ...
, a Microsoft subsidiary.


Implementations

Microsoft is leading the development of the open-source reference C# compilers and set of tools. The first compiler, Roslyn, compiles into intermediate language (IL), and the second one, RyuJIT, is a JIT (just-in-time) compiler, which is dynamic and does on-the-fly optimization and compiles the IL into native code for the front-end of the CPU. RyuJIT is open source and written in C++. Roslyn is entirely written in
managed code Managed code is computer program code that requires and will execute only under the management of a Common Language Infrastructure (CLI); Virtual Execution System (VES); virtual machine, e.g. .NET, CoreFX, or .NET Framework; Common Language Runt ...
(C#), has been opened up and functionality surfaced as APIs. It is thus enabling developers to create refactoring and diagnostics tools. Two branches of official implementation are .NET Framework (closed-source, Windows-only) and .NET Core (open-source, cross-platform); they eventually converged into one open-source implementation: .NET 5.0. At .NET Framework 4.6, a new JIT compiler replaced the former. Other C# compilers (some of which include an implementation of the Common Language Infrastructure and .NET class libraries): *
Mono Mono may refer to: Common meanings * Infectious mononucleosis, "the kissing disease" * Monaural, monophonic sound reproduction, often shortened to mono * Mono-, a numerical prefix representing anything single Music Performers * Mono (Japanese b ...
, a Microsoft-sponsored project provides an open-source C# compiler, a complete open-source implementation of the CLI (including the required framework libraries as they appear in the ECMA specification,) and a nearly complete implementation of the NET class libraries up to .NET Framework 3.5. * The Elements tool chain from
RemObjects RemObjects Software is an American software company founded in 2002 by Alessandro Federici and Marc Hoffman. It develops and offers tools and libraries for software developers on a variety of development platforms, including Embarcadero Delphi, Mi ...
includes RemObjects C#, which compiles C# code to .NET's
Common Intermediate Language Common Intermediate Language (CIL), formerly called Microsoft Intermediate Language (MSIL) or Intermediate Language (IL), is the intermediate language binary instruction set defined within the Common Language Infrastructure (CLI) specification. ...
,
Java bytecode In computing, Java bytecode is the bytecode-structured instruction set of the Java virtual machine (JVM), a virtual machine that enables a computer to run programs written in the Java programming language and several other programming langua ...
,
Cocoa Cocoa may refer to: Chocolate * Chocolate * ''Theobroma cacao'', the cocoa tree * Cocoa bean, seed of ''Theobroma cacao'' * Chocolate liquor, or cocoa liquor, pure, liquid chocolate extracted from the cocoa bean, including both cocoa butter and ...
, Android bytecode,
WebAssembly WebAssembly (sometimes abbreviated Wasm) defines a portable binary-code format and a corresponding text format for executable programs as well as software interfaces for facilitating interactions between such programs and their host environment ...
, and native machine code for Windows, macOS, and Linux. *The
DotGNU DotGNU is a decommissioned part of the GNU Project that started in January 2001. DotGNU aims to provide a free software replacement for Microsoft's .NET Framework by Free Software Foundation. Other goals of the project are better support for non- ...
project (now discontinued) also provided an open-source C# compiler, a nearly complete implementation of the Common Language Infrastructure including the required framework libraries as they appear in the ECMA specification, and subset of some of the remaining Microsoft proprietary .NET class libraries up to .NET 2.0 (those not documented or included in the ECMA specification, but included in Microsoft's standard .NET Framework distribution). The
Unity game engine Unity is a cross-platform game engine developed by Unity Technologies, first announced and released in June 2005 at Apple Worldwide Developers Conference as a Mac OS X game engine. The engine has since been gradually extended to support a var ...
uses C# as its primary scripting language. The Godot game engine has implemented an optional C# module thanks to a donation of $24,000 from Microsoft.


See also

;C# topics * C# syntax * Comparison of C# and Java * Comparison of C# and Visual Basic .NET * .NET standard libraries ;IDEs *
Visual Studio Visual Studio is an integrated development environment (IDE) from Microsoft. It is used to develop computer programs including web site, websites, web apps, web services and mobile apps. Visual Studio uses Microsoft software development platfor ...
*
Microsoft Visual Studio Express Microsoft Visual Studio Express is a set of integrated development environments (IDEs) that Microsoft developed and released free of charge. They are function-limited version of the non-free Visual Studio and require mandatory registration. Exp ...
*
Visual Studio Code Visual Studio Code, also commonly referred to as VS Code, is a source-code editor made by Microsoft with the Electron Framework, for Windows, Linux and macOS. Features include support for debugging, syntax highlighting, intelligent code comple ...
*
MonoDevelop MonoDevelop (also known as Xamarin Studio) is an open-source integrated development environment for Linux, macOS, and Windows. Its primary focus is development of projects that use Mono and .NET Framework. MonoDevelop integrates features similar t ...
*
Morfik Morfik Technology Pty Ltd. is an Australian software company that was acquired by Altium in 2010. The company is known for developing a set of visual designers, compilers and a Framework combined in an Integrated development environment (IDE ...
*
SharpDevelop SharpDevelop (also styled as #develop) is a discontinued free and open source integrated development environment (IDE) for the .NET Framework, Mono, Gtk# and Glade# platforms. It supports development in C#, Visual Basic .NET, Boo, F#, IronPyt ...
* Turbo C# * Rider *
Xamarin Studio Xamarin is a Microsoft-owned San Francisco-based software company founded in May 2011 by the engineers that created Mono, Xamarin.Android (formerly Mono for Android) and Xamarin.iOS (formerly MonoTouch), which are cross-platform implementation ...
*
LINQPad LINQPad is a software utility targeted at .NET Framework and .NET Core development. It is used to interactively query SQL databases (among other data sources such as OData or WCF Data Services WCF Data Services (formerly ADO.NET Data Services ...


Notes


References


Further reading

* *


External links


C# Language Specification

C# Programming Guide

ISO C# Language Specification

C# Compiler Platform ("Roslyn") source code
{{Authority control 2000 software American inventions Programming languages .NET programming languages Class-based programming languages Ecma standards Functional languages IEC standards ISO standards Microsoft programming languages Multi-paradigm programming languages Programming languages created in 2000 Programming languages with an ISO standard Statically typed programming languages