C20,.C,.cc,.cpp,.cxx,.c,.h,.hh,.hpp,.hxx,.hWebsiteMajor,Influenced by,Influenced,. at WikibooksC ( ) is a created by as an extension of the, or 'C with '. The language has expanded significantly over time, and modern C has, and features in addition to facilities for manipulation. It is almost always implemented as a, and many vendors provide, including the, and, so it is available on many platforms.C was designed with a bias toward and, resource-constrained software and large systems, with, efficiency¸ and flexibility of use as its design highlights.
C has also been found useful in many other contexts, with key strengths being software infrastructure and resource-constrained applications, including, (e.g., or servers), and performance-critical applications (e.g. Or ).C is standardized by the (ISO), with the latest standard version ratified and published by ISO in December 2017 as (informally known as ).
The C programming language was initially standardized in 1998 as ISO/IEC, which was then amended by the, and standards. The current C17 standard supersedes these with new features and an enlarged. Before the initial standardization in 1998, C was developed by Danish computer scientist at since 1979 as an extension of the; he wanted an efficient and flexible language similar to C that also provided for program organization. Is the next planned standard, keeping with the current trend of a new version every three years. The creator of CIn 1979, a Danish, began work on ' C with ', the predecessor to C.
The motivation for creating a new language originated from Stroustrup's experience in programming for his PhD thesis. Stroustrup found that had features that were very helpful for large software development, but the language was too slow for practical use, while was fast but too low-level to be suitable for large software development. When Stroustrup started working in, he had the problem of analyzing the with respect to.
Remembering his Ph.D. Experience, Stroustrup set out to enhance the language with -like features. C was chosen because it was general-purpose, fast, portable and widely used. As well as C and Simula's influences, other languages also influenced this new language, including, and.Initially, Stroustrup's 'C with Classes' added features to the C compiler, Cpre, including, and.In 1982, Stroustrup started to develop a successor to C with Classes, which he named 'C' ( being the in C) after going through several other names. New features were added, including, function name and, references, constants, type-safe free-store memory allocation (new/delete), improved type checking, and BCPL style single-line comments with two forward slashes ( //). Furthermore, Stroustrup developed a new, standalone compiler for C,.In 1985, the first edition of was released, which became the definitive reference for the language, as there was not yet an official standard.
The first commercial implementation of C was released in October of the same year.In 1989, C 2.0 was released, followed by the updated second edition of The C Programming Language in 1991. New features in 2.0 included multiple inheritance, abstract classes, static member functions, and protected members. In 1990, The Annotated C Reference Manual was published. This work became the basis for the future standard. Later feature additions included, new, and a.In 1998, C98 was released, standardizing the language, and a minor update was released in 2003.After C98, C evolved relatively slowly until, in 2011, the standard was released, adding numerous new features, enlarging the standard library further, and providing more facilities to C programmers.
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After a minor update released in December 2014, various new additions were introduced in, and further changes planned for 2020.As of 2019, C is now the fourth most popular programming language, behind, C, and.On January 3, 2018, Stroustrup was announced as the 2018 winner of the for Engineering, 'for conceptualizing and developing the C programming language'. Etymology According to Stroustrup, 'the name signifies the evolutionary nature of the changes from C'.
This name is credited to Rick Mascitti (mid-1983) and was first used in December 1983. When Mascitti was questioned informally in 1992 about the naming, he indicated that it was given in a spirit. See also: andenable. C supports function, class, alias, and variable templates. Templates may be parameterized by types, compile-time constants, and other templates. Templates are implemented by instantiation at compile-time.
To instantiate a template, compilers substitute specific arguments for a template's parameters to generate a concrete function or class instance. Some substitutions are not possible; these are eliminated by an overload resolution policy described by the phrase ' (SFINAE).
Templates are a powerful tool that can be used for, and code optimization, but this power implies a cost. Template use may increase code size, because each template instantiation produces a copy of the template code: one for each set of template arguments, however, this is the same or smaller amount of code that would be generated if the code was written by hand. This is in contrast to run-time generics seen in other languages (e.g., ) where at compile-time the type is erased and a single template body is preserved.Templates are different from: while both of these compile-time language features enable conditional compilation, templates are not restricted to lexical substitution.
Templates are aware of the semantics and type system of their companion language, as well as all compile-time type definitions, and can perform high-level operations including programmatic flow control based on evaluation of strictly type-checked parameters. Macros are capable of conditional control over compilation based on predetermined criteria, but cannot instantiate new types, recurse, or perform type evaluation and in effect are limited to pre-compilation text-substitution and text-inclusion/exclusion. In other words, macros can control compilation flow based on pre-defined symbols but cannot, unlike templates, independently instantiate new symbols. Templates are a tool for static (see below) and.In addition, templates are a compile time mechanism in C that is, meaning that any computation expressible by a computer program can be computed, in some form, by a prior to runtime.In summary, a template is a compile-time parameterized function or class written without knowledge of the specific arguments used to instantiate it. After instantiation, the resulting code is equivalent to code written specifically for the passed arguments. In this manner, templates provide a way to decouple generic, broadly applicable aspects of functions and classes (encoded in templates) from specific aspects (encoded in template parameters) without sacrificing performance due to abstraction.Objects. Main article:C introduces (OOP) features to C.
It offers, which provide the four features commonly present in OOP (and some non-OOP) languages:,. One distinguishing feature of C classes compared to classes in other programming languages is support for deterministic, which in turn provide support for the (RAII) concept.Encapsulation is the hiding of information to ensure that data structures and operators are used as intended and to make the usage model more obvious to the developer. C provides the ability to define classes and functions as its primary encapsulation mechanisms. Within a class, members can be declared as either public, protected, or private to explicitly enforce encapsulation.
A public member of the class is accessible to any function. A private member is accessible only to functions that are members of that class and to functions and classes explicitly granted access permission by the class ('friends'). A protected member is accessible to members of classes that inherit from the class in addition to the class itself and any friends.The object-oriented principle ensures the encapsulation of all and only the functions that access the internal representation of a type. C supports this principle via member functions and friend functions, but it does not enforce it. Programmers can declare parts or all of the representation of a type to be public, and they are allowed to make public entities not part of the representation of a type.
Therefore, C supports not just object-oriented programming, but other decomposition paradigms such as.It is generally considered good practice to make all private or protected, and to make public only those functions that are part of a minimal interface for users of the class. This can hide the details of data implementation, allowing the designer to later fundamentally change the implementation without changing the interface in any way. Inheritance allows one data type to acquire properties of other data types. Inheritance from a may be declared as public, protected, or private.
This access specifier determines whether unrelated and derived classes can access the inherited public and protected members of the base class. Only public inheritance corresponds to what is usually meant by 'inheritance'. The other two forms are much less frequently used. If the access specifier is omitted, a 'class' inherits privately, while a 'struct' inherits publicly. Base classes may be declared as virtual; this is called. Virtual inheritance ensures that only one instance of a base class exists in the inheritance graph, avoiding some of the ambiguity problems of multiple inheritance.is a C feature not found in most other languages, allowing a class to be derived from more than one base class; this allows for more elaborate inheritance relationships.
For example, a 'Flying Cat' class can inherit from both 'Cat' and 'Flying Mammal'. Some other languages, such as or, accomplish something similar (although more limited) by allowing inheritance of multiple while restricting the number of base classes to one (interfaces, unlike classes, provide only declarations of member functions, no implementation or member data). An interface as in C# and Java can be defined in C as a class containing only pure virtual functions, often known as an or 'ABC'.
The member functions of such an abstract base class are normally explicitly defined in the derived class, not inherited implicitly. C virtual inheritance exhibits an ambiguity resolution feature called.Operators and operator overloading Operators that cannot be overloadedOperatorSymbolScope resolution operator::Conditional operator?:dot operator.Member selection operator.' sizeof' operatorsizeof'typeid' operatortypeid. Main article:C provides more than 35 operators, covering basic arithmetic, bit manipulation, indirection, comparisons, logical operations and others. Almost all operators can be for user-defined types, with a few notable exceptions such as member access (. And.) as well as the conditional operator.
The rich set of overloadable operators is central to making user-defined types in C seem like built-in types.Overloadable operators are also an essential part of many advanced C programming techniques, such as. Overloading an operator does not change the precedence of calculations involving the operator, nor does it change the number of operands that the operator uses (any operand may however be ignored by the operator, though it will be evaluated prior to execution). Overloaded ' &&' and ' ' operators lose their property.Polymorphism. See also: andallows programs to declare multiple functions having the same name but with different arguments (i.e. The functions are distinguished by the number or types of their. Thus, the same function name can refer to different functions depending on the context in which it is used.
The type returned by the function is not used to distinguish overloaded functions and would result in a compile-time error message.When declaring a function, a programmer can specify for one or more parameters a. Doing so allows the parameters with defaults to optionally be omitted when the function is called, in which case the default arguments will be used. When a function is called with fewer arguments than there are declared parameters, explicit arguments are matched to parameters in left-to-right order, with any unmatched parameters at the end of the parameter list being assigned their default arguments. In many cases, specifying default arguments in a single function declaration is preferable to providing overloaded function definitions with different numbers of parameters.in C provide a sophisticated mechanism for writing generic, polymorphic code (i.e. In particular, through the, it's possible to implement a form of static polymorphism that closely mimics the syntax for overriding virtual functions. Because C templates are type-aware and, they can also be used to let the compiler resolve recursive conditionals and generate substantial programs through. Contrary to some opinion, template code will not generate a bulk code after compilation with the proper compiler settings.
Dynamic polymorphism Inheritance. See also:Variable pointers and references to a base class type in C can also refer to objects of any derived classes of that type. This allows arrays and other kinds of containers to hold pointers to objects of differing types (references cannot be directly held in containers). This enables dynamic (run-time) polymorphism, where the referred objects can behave differently, depending on their (actual, derived) types.C also provides the dynamiccast operator, which allows code to safely attempt conversion of an object, via a base reference/pointer, to a more derived type: downcasting. The attempt is necessary as often one does not know which derived type is referenced.
( Upcasting, conversion to a more general type, can always be checked/performed at compile-time via staticcast, as ancestral classes are specified in the derived class's interface, visible to all callers.) dynamiccast relies on (RTTI), metadata in the program that enables differentiating types and their relationships. If a dynamiccast to a pointer fails, the result is the nullptr constant, whereas if the destination is a reference (which cannot be null), the cast throws an exception. Objects known to be of a certain derived type can be cast to that with staticcast, bypassing RTTI and the safe runtime type-checking of dynamiccast, so this should be used only if the programmer is very confident the cast is, and will always be, valid.Virtual member functions Ordinarily, when a function in a derived class a function in a base class, the function to call is determined by the type of the object. A given function is overridden when there exists no difference in the number or type of parameters between two or more definitions of that function.
Hence, at compile time, it may not be possible to determine the type of the object and therefore the correct function to call, given only a base class pointer; the decision is therefore put off until runtime. This is called. Or methods allow the most specific implementation of the function to be called, according to the actual run-time type of the object. In C implementations, this is commonly done using.
If the object type is known, this may be bypassed by prepending a before the function call, but in general calls to virtual functions are resolved at run time.In addition to standard member functions, operator overloads and destructors can be virtual. As a rule of thumb, if any function in the class is virtual, the destructor should be as well. As the type of an object at its creation is known at compile time, constructors, and by extension copy constructors, cannot be virtual. Nonetheless a situation may arise where a copy of an object needs to be created when a pointer to a derived object is passed as a pointer to a base object. In such a case, a common solution is to create a clone (or similar) virtual function that creates and returns a copy of the derived class when called.A member function can also be made 'pure virtual' by appending it with = 0 after the closing parenthesis and before the semicolon. A class containing a pure virtual function is called an abstract class. Objects cannot be created from an abstract class; they can only be derived from.
Any derived class inherits the virtual function as pure and must provide a non-pure definition of it (and all other pure virtual functions) before objects of the derived class can be created. A program that attempts to create an object of a class with a pure virtual member function or inherited pure virtual member function is ill-formed.Lambda expressions C provides support for, also known as lambda expressions, with the following form. Main article:The C consists of two parts: the core language and the standard library. Main article:Despite its widespread adoption, some notable programmers have criticized the C language, including, and.One of the most often criticised points of C is its perceived complexity as a language, with the criticism that a large number of non-orthogonal features in practice necessitates restricting code to subset of C, thus eschewing the readability benefits of common style and idioms. As expressed by:I think C was pushed well beyond its complexity threshold and yet there are a lot of people programming it. But what you do is you force people to subset it. So almost every shop that I know of that uses C says, “Yes, we’re using C but we’re not doing multiple-implementation inheritance and we’re not using operator overloading.” There are just a bunch of features that you’re not going to use because the complexity of the resulting code is too high.
And I don’t think it’s good when you have to start doing that. You lose this programmer portability where everyone can read everyone else’s code, which I think is such a good thing.(1993, commenting on pre-standardized C), who said of that 'to think of programming in C' 'would make him physically ill':The problem that I have with them today is that. C is too complicated. At the moment, it's impossible for me to write portable code that I believe would work on lots of different systems, unless I avoid all exotic features. Whenever the C language designers had two competing ideas as to how they should solve some problem, they said 'OK, we'll do them both'.
So the language is too baroque for my taste., who was a colleague of Stroustrup at Bell Labs, gives his assessment:It certainly has its good points. But by and large I think it’s a bad language. It does a lot of things half well and it’s just a garbage heap of ideas that are mutually exclusive. Everybody I know, whether it’s personal or corporate, selects a subset and these subsets are different.
So it’s not a good language to transport an algorithm—to say, “I wrote it; here, take it.” It’s way too big, way too complex. And it’s obviously.Stroustrup campaigned for years and years and years, way beyond any sort of technical contributions he made to the language, to get it adopted and used.
And he sort of ran all the standards committees with a whip and a chair. And he said “no” to no one. He put every feature in that language that ever existed. It wasn’t cleanly designed—it was just the union of everything that came along. And I think it suffered drastically from that.However, also a colleague at Bell Labs, disputes this assessment:C has been enormously influential. Lots of people say C is too big and too complicated etc.
But in fact it is a very powerful language and pretty much everything that is in there is there for a really sound reason: it is not somebody doing random invention, it is actually people trying to solve real world problems. Now a lot of the programs that we take for granted today, that we just use, are C programs.Stroustrup himself comments that C semantics are much cleaner than its syntax: 'within C, there is a much smaller and cleaner language struggling to get out'.Other complaints may include a lack of or, long compilation times, perceived, and verbose error messages, particularly from template metaprogramming.
See also. Naugler, David (May 2007). 'C# 2.0 for C and Java programmer: conference workshop'.
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And what about compiled code size? Each were compiled with the command g.cpp -O3. Non-template version: 8140 bytes, template version: 8028 bytes!.; (2004). C Coding Standards: 101 Rules, Guidelines, and Best Practices. Addison-Wesley. Henricson, Mats; Nyquist, Erik (1997).
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Retrieved 3 February 2016.Further reading.