C Sharp (programming language)

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This article is about a programming language. For other uses, see C-sharp (disambiguation).
The correct title of this article is C# (programming language). The substitution or omission of the # is because of technical restrictions.
C Sharp wordmark.svg
Paradigms multi-paradigm: structured, imperative, object-oriented, event-driven, task-driven, functional, generic, reflective, concurrent
Designed by Microsoft
Developer Microsoft
Appeared in 2000
5.0 / August 15, 2012; 2 years ago (2012-08-15)
static, dynamic,[1] strong, safe, nominative, partially inferred

Major implementations
Visual C#, .NET Framework, Mono, DotGNU
, Spec#, Polyphonic C#
Influenced by C++,[2] Eiffel, Java,[2] Modula-3, Object Pascal,[3] ML, Icon, Haskell, , F#[note 1]
Influenced D, Dart,[4] F#, Java,[5] Kotlin, Monkey, Nemerle, Swift,[6] Vala
Platform Common Language Infrastructure
License CLR is proprietary, Mono compiler is dual GPLv3, MIT/X11 and libraries are LGPLv2, DotGNU is dual GPL and LGPLv2


C# is intended to be a simple, modern, general-purpose, object-oriented programming language.[7] Its development team is led by Anders Hejlsberg. The most recent version is C# 5.0, which was released on August 15, 2012.

Design goals[edit]

The ECMA standard lists these design goals for C#:[7]

  • The C# language is intended to be a simple, modern, general-purpose, object-oriented programming language.
  • Source code portability is very important, as is programmer portability, especially for those programmers already familiar with C and C++.
  • Support for internationalization is very important.


The name "C sharp" was inspired by musical notation where a sharp indicates that the written note should be made a semitone higher in pitch.[8] This is similar to the language name of C++, where "++" indicates that a variable should be incremented by 1. The sharp symbol also resembles a ligature of four "+" symbols (in a two-by-two grid), further implying that the language is an increment of C++.[9]

Due to technical limitations of display (standard fonts, browsers, etc.) and the fact that the sharp symbol (U+266F music sharp sign (HTML &#9839;)) is not present on the standard keyboard, the number sign (U+0023 # number sign (HTML &#35;)) was chosen to represent the sharp symbol in the written name of the programming language.[10] This convention is reflected in the ECMA-334 C# Language Specification.[7] However, when it is practical to do so (for example, in advertising or in box art[11]), Microsoft uses the intended musical symbol.

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), and the functional programming language F#.[12] The original implementation of Eiffel for .NET was called Eiffel#,[13] a name retired since the full Eiffel language is now supported. The suffix has also been used for libraries, such as Gtk# (a .NET wrapper for GTK+ and other GNOME libraries) and Cocoa# (a wrapper for Cocoa).


During the development of the .NET Framework, the class libraries were originally written using a managed code compiler system called Simple Managed C (SMC).[14][15][16] In January 1999, Anders Hejlsberg formed a team to build a new language at the time called Cool, which stood for "C-like Object Oriented Language".[17] 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, the language had been renamed C#, and the class libraries and ASP.NET runtime had been ported to C#.

C#'s principal designer and lead architect at Microsoft is Anders Hejlsberg, who was previously involved with the design of Turbo Pascal, Embarcadero Delphi (formerly CodeGear Delphi, Inprise Delphi and Borland Delphi), and Visual J++. In interviews and technical papers he has stated that flaws[citation needed] in most major programming languages (e.g. C++, Java, Delphi, and Smalltalk) drove the fundamentals of the Common Language Runtime (CLR), which, in turn, drove the design of the C# language itself.

James Gosling, who created the Java programming language in 1994, and Bill Joy, a co-founder of Sun Microsystems, the originator of Java, called C# an "imitation" of Java; Gosling further said that "[C# is] sort of Java with reliability, productivity and security deleted."[18][19] 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,"[20] "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 and unboxing, we'll have a very similar feature in Java."[21] In July 2000, Anders Hejlsberg said that C# is "not a Java clone" and is "much closer to C++" in its design.[22]

Since the release of C# 2.0 in November 2005, the C# and Java languages have evolved on increasingly divergent trajectories, becoming somewhat less similar. 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.[23] By contrast, Java's generics are essentially a language syntax feature, and they do not affect the generated byte code, because the compiler performs type erasure on the generic type information after it has verified its correctness.[24]

Furthermore, C# has added several major features to accommodate functional-style programming, culminating in the LINQ extensions released with C# 3.0 and its supporting framework of lambda expressions, extension methods, and anonymous types.[25] 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.[26]


C# was originally submitted for review to the ISO subcommittee JTC 1/SC 22[28] under ISO/IEC 23270:2003,[29] which is now withdrawn. It was then approved under ISO/IEC 23270:2006.[30]


Version Language specification Date .NET Framework Visual Studio
ECMA ISO/IEC Microsoft
C# 1.2 October 2003 April 2003 .NET Framework 1.1 Visual Studio .NET 2003
C# 2.0 June 2006 September 2006 September 2005[note 3] November 2005 .NET Framework 2.0 Visual Studio 2005
C# 3.0 None[note 4] August 2007 November 2007

.NET Framework 2.0 (Except LINQ/Query Extensions)[31]
.NET Framework 3.0 (Except LINQ/Query Extensions)[31]
.NET Framework 3.5

Visual Studio 2008
Visual Studio 2010
C# 5.0 June 2013 August 2012 .NET Framework 4.5 Visual Studio 2012
Visual Studio 2013
Summary of versions
C# 2.0 C# 3.0 C# 4.0 C# 5.0 [32] Future
  • Dynamic binding[36]
  • Named and optional arguments[36]
  • Generic co- and contravariance[36]
  • Embedded interop types ("NoPIA")[36]
  • Asynchronous methods[37]
  • Caller info attributes[37]
C# 5.0
  • Compiler-as-a-service (Roslyn)
C# 6.0 Planned/Done
  • Declaration expressions[38]
  • Import of static type members into namespace[38]
  • Exception filters[38]
  • Await in catch/finally blocks[38]
  • Default values for getter-only properties[38]
  • Expression-bodied members[38]
  • Parameter arrays for IEnumerable interfaces[38]
  • Null propagator (Succinct null checking)[38]
C# 6.0 Maybe
  • String Interpolation[38]
  • Constructor type inference[38]
  • Succinct syntax for primary constructors[38]


Main article: C Sharp syntax


Distinguishing features[edit]

Note: The following description is based on the language standard and other documents listed in the "External links" section.

By design, C# is the programming language that most directly reflects the underlying Common Language Infrastructure (CLI).[39] 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 (CIL), or generate any other specific format. Theoretically, a C# compiler could generate machine code like traditional compilers of C++ or Fortran. Some notable features of C# that distinguish it from C and C++ (and Java, where noted) are:

  • Like C++, and unlike Java, C# programmers must use the keyword virtual to allow methods to be overridden by subclasses.
  • C# has support for strongly-typed function pointers via the keyword delegate.
  • 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 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 a value-type, array, string, or a block of memory allocated on a stack. Code that is not marked as unsafe can still store and manipulate pointers through the System.IntPtr type, but it cannot dereference them.
  • In addition to the try...catch construct to handle exceptions, C# has a try...finally construct to guarantee execution of the code in the finally block, whether an exception occurs or not. This is present in other programming languages like Java and Python.
  • C#, supports connections to various types and providers of databases, from SQLite, MySQL, Microsoft SQL Server (MSSQL), Oracle, etc. You might need to import 3rd party libraries to use some of the database, except MSSQL which is supported by default.
  • Multiple inheritance is not supported, although a class can implement any number of interfaces. This was a design decision by the language's lead architect to avoid complication and simplify architectural requirements throughout CLI. When implementing multiple interfaces that contain a method with the same signature, C# allows the programmer to implement each method depending on which interface that method is being called through, or, like Java, allows the programmer to implement the method once and have that be the single invocation on a call through any of the class's interfaces.
  • C#, unlike Java, supports operator overloading. Only the most commonly overloaded operators in C++ may be overloaded in C#.
  • Enumeration members are placed in their own scope.
  • C# provides properties as syntactic sugar for a common pattern in which a pair of methods, accessor (getter) and mutator (setter) encapsulate operations on a single attribute of a class. No redundant method signatures for the getter/setter implementations need be written, and the property may be accessed using attribute syntax rather than more verbose method calls.
  • Though primarily an imperative language, C# 2.0 offered limited support for functional programming through first-class functions and closures in the form of anonymous delegates. C# 3.0 expanded support for functional programming with the introduction of a light weight syntax for lambda expressions, extension methods (an affordance for modules), and a list comprehension syntax in the form of a "query comprehension" language.

Common type system[edit]



Categories of data types[edit]

CTS separates data types into two categories:[41]

  1. Reference types
  2. Value types



Both type categories are extensible with user-defined types.

Boxing and unboxing[edit]

Boxing is the operation of converting a value-type object into a value of a corresponding reference type.[41] 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.[41] 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).[42]


int foo1 = 42;         // Value type.
object bar = foo1;     // foo is boxed to bar.


Generics were added to version 2.0 of the C# language. Generics use type parameters, which make it possible to design classes and methods that do not specify the type used until the class or method is instantiated. The main advantage is that one can use generic type parameters to create classes and methods that can be used without incurring the cost of runtime casts or boxing operations, as shown here:[43]

// Declare the generic class.
public class GenericList<T>
    void Add(T input) { }
class TestGenericList
    private class ExampleClass { }
    static void Main()
        // Declare a list of type int.
        GenericList<int> list1 = new GenericList<int>();
        // Declare a list of type string.
        GenericList<string> list2 = new GenericList<string>();
        // Declare a list of type ExampleClass.
        GenericList<ExampleClass> list3 = new GenericList<ExampleClass>();

When compared with C++ templates, C# generics can provide enhanced safety, but also have somewhat limited capabilities.[44] For example, it is not possible to call arithmetic operators on a C# generic type.[45]


C# features "preprocessor directives"[46] (though it does not have an actual preprocessor) based on the C preprocessor that allow programmers to define symbols, but not macros. Conditionals such as #if, #endif, and #else are also provided. Directives such as #region give hints to editors for code folding.

public class Foo
    #region Constructors
    public Foo() {}
    public Foo(int firstParam) {}
    #region Procedures
    public void IntBar(int firstParam) {}
    public void StrBar(string firstParam) {}
    public void BoolBar(bool firstParam) {}

Code comments[edit]

C# utilizes a double slash (//) to indicate the rest of the line is a comment. This is inherited from C++.

public class Foo
    // a comment
    public static void Bar(int firstParam) {}  // also a comment

Multi-line comments can start with slash-asterisk (/*) and end asterisk-slash (*/). This is inherited from standard C.

public class Foo
    /* A Multi-Line
       comment  */
    public static void Bar(int firstParam) {}

XML documentation system[edit]

C#'s documentation system is similar to Java's Javadoc, but based on XML. Two methods of documentation are currently supported by the C# compiler.

Single-line documentation comments, such as those commonly found in Visual Studio generated code, are indicated on a line beginning with ///.

public class Foo
    /// <summary>A summary of the method.</summary>
    /// <param name="firstParam">A description of the parameter.</param>
    /// <remarks>Remarks about the method.</remarks>
    public static void Bar(int firstParam) {}

Multi-line documentation comments, while defined in the version 1.0 language specification, were not supported until the .NET 1.1 release.[47] These comments start with slash-asterisk-asterisk (/**) and end asterisk-slash (*/).[48]

public class Foo
    /** <summary>A summary of the method.</summary>
     *  <remarks>Remarks about the method.</remarks> */
    public static void Bar(int firstParam) {}

Note there are some stringent criteria regarding white space and XML documentation when using the slash/asterisk/asterisk (/**) technique.

This code block:

 * <summary>
 * A summary of the method.</summary>*/

produces a different XML comment from this code block:[48]

 * <summary>
   A summary of the method.</summary>*/

Syntax for documentation comments and their XML markup is defined in a non-normative annex of the ECMA C# standard. The same standard also defines rules for processing of such comments, and their transformation to a plain XML document with precise rules for mapping of CLI identifiers to their related documentation elements. This allows any C# IDE or other development tool to find documentation for any symbol in the code in a certain well-defined way.



"Hello, world" example[edit]


using System;
class Program
    static void Main()
        Console.WriteLine("Hello, world!");

The effect is to write the following text to the output console:

Hello, world!

Each line has a purpose:

using System;

The above line of code tells the compiler to use System as a candidate prefix for types used in the source code. In this case, when the compiler sees use of the Console type later in the source code, it tries to find a type named Console, first in the current assembly, followed by all referenced assemblies. In this case the compiler fails to find such a type, since the name of the type is actually System.Console. The compiler then attempts to find a type named System.Console by using the System prefix from the using statement, and this time it succeeds. The using statement allows the programmer to state all candidate prefixes to use during compilation instead of always using full type names.

class Program


static void Main()


Console.WriteLine("Hello, world!");


A GUI example:

using System.Windows.Forms;
class Program
    static void Main()
        MessageBox.Show("Hello, world!");

This example is similar to the previous example, except that it generates a dialog box that contains the message "Hello, world!" instead of writing it to the console.

Standardization and licensing[edit]



In July 2005, ECMA submitted the standards and related TRs to ISO/IEC JTC 1 via the latter's Fast-Track process. This process usually takes 6–9 months.


Microsoft has 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.[49] Microsoft has also agreed not to enforce patents relating to Novell products against Novell's paying customers[50] with the exception of a list of products that do not explicitly mention C#, .NET or Novell's implementation of .NET (The Mono Project).[51] However, Novell maintains that Mono does not infringe any Microsoft patents.[52] Microsoft has 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.[53]


The reference C# compiler is Microsoft Visual C#, which is closed-source.

Microsoft is leading the development of a new open source C# compiler and set of tools, previously codenamed "Roslyn". The compiler, which is entirely written in managed code (C#), has been opened up and functionality surfaced as APIs. It is thus enabling developers to create refactoring and diagnostics tools.

Other C# compilers exist, often including an implementation of the Common Language Infrastructure and the .NET class libraries up to .NET 2.0:

  • The Mono project provides an open source C# compiler, a complete open source implementation of the Common Language Infrastructure including the required framework libraries as they appear in the ECMA specification, and a nearly complete implementation of the Microsoft proprietary .NET class libraries up to .NET 3.5. As of Mono 2.6, no plans exist to implement WPF; WF is planned for a later release; and there are only partial implementations of LINQ to SQL and WCF.[54]
  • Microsoft's Rotor project (currently called Shared Source Common Language Infrastructure) (licensed for educational and research use only) provides a shared source implementation of the CLR runtime and a C# compiler, and a subset of the required Common Language Infrastructure framework libraries in the ECMA specification (up to C# 2.0, and supported on Windows XP only).

See also[edit]


  1. ^ for async
  3. ^ The Microsoft C# 2.0 specification document only contains the new 2.0 features. For older features use the 1.2 specification above.
  4. ^ No ECMA or ISO/IEC specifications exist for C# 3.0, 4.0 or 5.0.


  2. ^ a b Naugler, David (May 2007). "C# 2.0 for C++ and Java programmer: conference workshop". Journal of Computing Sciences in Colleges 22 (5). Although C# has been strongly influenced by Java it has also been strongly influenced by C++ and is best viewed as a descendant of both C++ and Java. 
  4. ^ "Web Languages and VMs: Fast Code is Always in Fashion. (V8, Dart) - Google I/O 2013". Google. Retrieved 22 December 2013. 
  6. ^ Lattner, Chris (2014-06-03). "Chris Lattner's Homepage". Chris Lattner. Retrieved 2014-06-03. The Swift language is the product of tireless effort from a team of language experts, documentation gurus, compiler optimization ninjas, and an incredibly important internal dogfooding group who provided feedback to help refine and battle-test ideas. Of course, it also greatly benefited from the experiences hard-won by many other languages in the field, drawing ideas from Objective-C, Rust, Haskell, Ruby, Python, C#, CLU, and far too many others to list. 
  7. ^ a b c C# Language Specification (4th ed.). Ecma International. June 2006. Retrieved January 26, 2012. 
  10. ^ "Microsoft C# FAQ". Microsoft. Retrieved March 25, 2008. [dead link]
  11. ^ "Visual C#.net Standard" (JPEG). Microsoft. September 4, 2003. Retrieved June 18, 2009. 
  12. ^ "F# FAQ". Microsoft Research. Retrieved June 18, 2009. [dead link]
  15. ^ "C# 3.0 New Features". Retrieved $1 $2.  Check date values in: |accessdate= (help)
  16. ^ Guthrie, Scott (November 28, 2006). "What language was ASP.Net originally written in?". Retrieved February 21, 2008. 
  24. ^ Bracha, Gilad (July 5, 2004). "Generics in the Java Programming Language". Sun Microsystems. Archived from the original on September 15, 2012. Retrieved March 21, 2011. 
  32. ^ Hejlsberg, Anders. "Future directions for C# and Visual Basic". C# lead architect. Channel 9. Retrieved September 21, 2011. 
  33. ^ a b c d e f g h i "What's new in the C# 2.0 Language and Compiler". Microsoft Developer Network. Microsoft. Retrieved 11 June 2014. 
  34. ^ a b c d e f g h Hejlsberg, Anders; Torgersen, Mads. "Overview of C# 3.0". Microsoft Developer Network. MIcrosoft. Retrieved 11 June 2014. 
  35. ^ Ghosh, Wriju. "C# 3.0 : Partial Methods". MSDN Blogs. Microsoft. Retrieved 11 June 2014. 
  37. ^ a b "An Introduction to New Features in C# 5.0". MSDN Blogs. Microsoft. Retrieved 11 June 2014. 
  38. ^ a b c d e f g h i j k "Language feature implementation status". Codeplex. Microsoft. Retrieved 11 June 2014. 
  39. ^ Visual Studio 2010 and .NET 4 Six-in-One. Wrox Press. 2010. ISBN 0470499486. 
  43. ^ "Generics (C# Programming Guide)". Microsoft. Retrieved August 7, 2011. 
  44. ^ "An Introduction to C# Generics". Microsoft. 
  45. ^ "Differences Between C++ Templates and C# Generics". Microsoft. 
  46. ^ "C# Preprocessor Directives". C# Language Reference. Microsoft. Retrieved June 18, 2009. 
  47. ^ Horton, Anson (September 11, 2006). "C# XML documentation comments FAQ". Retrieved December 11, 2007. 
  48. ^ a b "Delimiters for Documentation Tags". C# Programmer's Reference. Microsoft. January 1, 1970 GMT. Retrieved June 18, 2009.  Check date values in: |date= (help)
  49. ^ "Patent Pledge for Open Source Developers". 

Further reading[edit]

  • Drayton, Peter; Albahari, Ben; Neward, Ted (2002). C# Language Pocket Reference. O'Reilly. ISBN 0-596-00429-X. 
  • Petzold, Charles (2002). Programming Microsoft Windows with C#. Microsoft Press. ISBN 0-7356-1370-2. 

External links[edit]