Design goals
The Ecma standard lists these design goals for C#: * The language is intended to be a simple, modern, general-purpose,History
During the development of theName
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 higher in pitch. This is similar to the language name of C++, where "++" indicates that a variable should be incremented by 1 after being evaluated. 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++. Due to technical limitations of display (standard fonts, browsers, etc.) and the fact that the sharp symbol () is not present on most keyboard layouts, the number sign () 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# (fromVersions
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 are used to group statements. Statements are commonly grouped into methods (functions), methods into classes, and classes intoDistinguishing 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 generateTyping
C# supports strongly, implicitly typed variable declarations with the keywordvar
, 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 Metaprogramming
Metaprogramming can be achieved in several ways: * Reflection 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, 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 to the language. * Attributes are metadata 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) 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, the signature of a method is a declaration comprising in order: any optional accessibility keywords (such asprivate
), 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.
C# has support for strongly-typed function pointers 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. The properties can be simple accessor functions with a backing field, or implement getter and setter functions.
Since C# 3.0 the syntactic sugar of auto-implemented properties is available, where the accessor (getter) and mutator (setter) encapsulate operations on a single attribute 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 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 leaks 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 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# does not support multiple inheritance, although a class can implement any number of "interfaces
Interface or interfacing may refer to:
Academic journals
* ''Interface'' (journal), by the Electrochemical Society
* '' Interface, Journal of Applied Linguistics'', now merged with ''ITL International Journal of Applied Linguistics''
* '' Int ...
" (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 Handwriting, handwritten (and often Stylization, 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 ...
), 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 mo ...
, 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.
Language Integrated Query (LINQ)
C# has the ability to utilize LINQ 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-c ...
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 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. 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 (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
This article contains a list of libraries that can be used in .NET languages. These languages require .NET Framework, Mono, or .NET, which provide a basis for software development, platform independence, language interoperability and extensive f ...
.
Examples
Hello World
The following is a very simple C# program, a version of the classic " Hello world" 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 differently ...
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 mo ...
, 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 depe ...
, 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 mo ...
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 s ...
.
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, Washi ...
, 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 ser ...
co-sponsored the submission of specifications for C# as well as the Common Language Infrastructure (CLI) to the standards organization Ecma International. In December 2001, ECMA released ECMA-334 ''C# Language Specification''. C# became an 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
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 ...
(somewhat similar to C++ templates). 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 instr ...
are standardized under 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 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 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, .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 implementat ...
, 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 (Japanes ...
, 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 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 an ...
, 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 environmen ...
, 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 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
* MonoDevelop
* Morfik
* SharpDevelop
* Turbo C#
* Rider
* Xamarin Studio
* LINQPad
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