DANCER SWAPNILA

C++ (/ˌsiːˌplʌsˈplʌs/) is a 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 significantly over time, and modern C++ now has object-oriented, generic, and functional features in addition to facilities for low-level memory manipulation. It is almost always implemented as a compiled language, and many vendors provide C++ compilers, including the Free Software Foundation, LLVM, Microsoft, Intel, Oracle, and IBM, so it is available on many platforms.^[10]

C++ was designed with an orientation toward systems programming and embedded, resource-constrained software and large systems, with performance, efficiency, and flexibility of use as its design highlights.^[11] C++ has also been found useful in many other contexts, with key strengths being software infrastructure and resource-constrained applications,^[11] including desktop applications, video games, servers (e.g. e-commerce, web search, or databases), and performance-critical applications (e.g. telephone switches or space probes).^[12]

C++ is standardized by the International Organization for Standardization (ISO), with the latest standard version ratified and published by ISO in December 2020 as ISO/IEC 14882:2020 (informally known as C++20).^[13] The C++ programming language was initially standardized in 1998 as ISO/IEC 14882:1998, which was then amended by the C++03, C++11, C++14, and C++17 standards. The current C++20 standard supersedes these with new features and an enlarged standard library. Before the initial standardization in 1998, C++ was developed by Stroustrup at Bell Labs since 1979 as an extension of the C language; he wanted an efficient and flexible language similar to C that also provided high-level features for program organization.^[14] Since 2012, C++ has been on a three-year release schedule^[15] with C++23 as the next planned standard.^[16]

History[edit]

Bjarne Stroustrup, the creator of C++, in his AT&T New Jersey office c. 2000

In 1979, Bjarne Stroustrup, a Danish computer scientist, began work on "C with Classes", the predecessor to C++.^[17] The motivation for creating a new language originated from Stroustrup's experience in programming for his PhD thesis. Stroustrup found that Simula had features that were very helpful for large software development, but the language was too slow for practical use, while BCPL was fast but too low-level to be suitable for large software development. When Stroustrup started working in AT&T Bell Labs, he had the problem of analyzing the UNIX kernel with respect to distributed computing. Remembering his PhD experience, Stroustrup set out to enhance the C language with Simula-like features.^[18] 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 ALGOL 68, Ada, CLU and ML.

Initially, Stroustrup's "C with Classes" added features to the C compiler, Cpre, including classes, derived classes, strong typing, inlining and default arguments.^[19]

A quiz on C++11 features being given in Paris in 2015

In 1982, Stroustrup started to develop a successor to C with Classes, which he named "C++" (++ being the increment operator in C) after going through several other names. New features were added, including virtual functions, function name and operator overloading, 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++, Cfront.

In 1984, Stroustrup implemented the first stream input/output library. The idea of providing an output operator rather than a named output function was suggested by Doug McIlroy^[1] (who had previously suggested Unix pipes).

In 1985, the first edition of The C++ Programming Language was released, which became the definitive reference for the language, as there was not yet an official standard.^[20] The first commercial implementation of C++ was released in October of the same year.^[17]

In 1989, C++ 2.0 was released, followed by the updated second edition of The C++ Programming Language in 1991.^[21] New features in 2.0 included multiple inheritance, abstract classes, static member functions, const 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 templates, exceptions, namespaces, new casts, and a Boolean type.

In 1998, C++98 was released, standardizing the language, and a minor update (C++03) was released in 2003.

After C++98, C++ evolved relatively slowly until, in 2011, the C++11 standard was released, adding numerous new features, enlarging the standard library further, and providing more facilities to C++ programmers. After a minor C++14 update released in December 2014, various new additions were introduced in C++17.^[22] After becoming finalized in February 2020,^[23] a draft of the C++20 standard was approved on 4 September 2020 and officially published on 15 December 2020.^[24]^[25]

On January 3, 2018, Stroustrup was announced as the 2018 winner of the Charles Stark Draper Prize for Engineering, "for conceptualizing and developing the C++ programming language".^[26]

As of 2022 C++ ranked fourth on the TIOBE index, a measure of the popularity of programming languages, after Python, C and Java.^[27]

Etymology[edit]

According to Stroustrup, "the name signifies the evolutionary nature of the changes from C".^[28] This name is credited to Rick Mascitti (mid-1983)^[19] 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 tongue-in-cheek spirit. The name comes from C's ++ operator (which increments the value of a variable) and a common naming convention of using "+" to indicate an enhanced computer program.

During C++'s development period, the language had been referred to as "new C" and "C with Classes"^[19]^[29] before acquiring its final name.

Philosophy[edit]

Throughout C++'s life, its development and evolution has been guided by a set of principles:^[18]

It must be driven by actual problems and its features should be immediately useful in real world programs.
Every feature should be implementable (with a reasonably obvious way to do so).
Programmers should be free to pick their own programming style, and that style should be fully supported by C++.
Allowing a useful feature is more important than preventing every possible misuse of C++.
It should provide facilities for organising programs into separate, well-defined parts, and provide facilities for combining separately developed parts.
No implicit violations of the type system (but allow explicit violations; that is, those explicitly requested by the programmer).
User-created types need to have the same support and performance as built-in types.
Unused features should not negatively impact created executables (e.g. in lower performance).
There should be no language beneath C++ (except assembly language).
C++ should work alongside other existing programming languages, rather than fostering its own separate and incompatible programming environment.
If the programmer's intent is unknown, allow the programmer to specify it by providing manual control.

Standardization[edit]

Scene during the C++ standards committee meeting in Stockholm in 1996

C++ standards
Year	C++ Standard^[30]	Informal name
1998	ISO/IEC 14882:1998^[31]	C++98
2003	ISO/IEC 14882:2003^[32]	C++03
2011	ISO/IEC 14882:2011^[33]	C++11, C++0x
2014	ISO/IEC 14882:2014^[34]	C++14, C++1y
2017	ISO/IEC 14882:2017^[35]	C++17, C++1z
2020	ISO/IEC 14882:2020^[13]	C++20, C++2a

C++ is standardized by an ISO working group known as JTC1/SC22/WG21. So far, it has published six revisions of the C++ standard and is currently working on the next revision, C++23.

In 1998, the ISO working group standardized C++ for the first time as ISO/IEC 14882:1998, which is informally known as C++98. In 2003, it published a new version of the C++ standard called ISO/IEC 14882:2003, which fixed problems identified in C++98.

The next major revision of the standard was informally referred to as "C++0x", but it was not released until 2011.^[36] C++11 (14882:2011) included many additions to both the core language and the standard library.^[33]

In 2014, C++14 (also known as C++1y) was released as a small extension to C++11, featuring mainly bug fixes and small improvements.^[37] The Draft International Standard ballot procedures completed in mid-August 2014.^[38]

After C++14, a major revision C++17, informally known as C++1z, was completed by the ISO C++ committee in mid July 2017 and was approved and published in December 2017.^[39]

As part of the standardization process, ISO also publishes technical reports and specifications:

ISO/IEC TR 18015:2006^[40] on the use of C++ in embedded systems and on performance implications of C++ language and library features,
ISO/IEC TR 19768:2007^[41] (also known as the C++ Technical Report 1) on library extensions mostly integrated into C++11,
ISO/IEC TR 29124:2010^[42] on special mathematical functions, integrated into C++17
ISO/IEC TR 24733:2011^[43] on decimal floating-point arithmetic,
ISO/IEC TS 18822:2015^[44] on the standard filesystem library, integrated into C++17
ISO/IEC TS 19570:2015^[45] on parallel versions of the standard library algorithms, integrated into C++17
ISO/IEC TS 19841:2015^[46] on software transactional memory,
ISO/IEC TS 19568:2015^[47] on a new set of library extensions, some of which are already integrated into C++17,
ISO/IEC TS 19217:2015^[48] on the C++ concepts, integrated into C++20
ISO/IEC TS 19571:2016^[49] on the library extensions for concurrency, some of which are already integrated into C++20
ISO/IEC TS 19568:2017^[50] on a new set of general-purpose library extensions
ISO/IEC TS 21425:2017^[51] on the library extensions for ranges, integrated into C++20
ISO/IEC TS 22277:2017^[52] on coroutines, integrated into C++20
ISO/IEC TS 19216:2018^[53] on the networking library
ISO/IEC TS 21544:2018^[54] on modules, integrated into C++20
ISO/IEC TS 19570:2018^[55] on a new set of library extensions for parallelism
ISO/IEC TS 23619:2021^[56] on a new extensions for reflection

More technical specifications are in development and pending approval, including new set of concurrency extensions.^[57]

Language[edit]

The C++ language has two main components: a direct mapping of hardware features provided primarily by the C subset, and zero-overhead abstractions based on those mappings. Stroustrup describes C++ as "a light-weight abstraction programming language [designed] for building and using efficient and elegant abstractions";^[11] and "offering both hardware access and abstraction is the basis of C++. Doing it efficiently is what distinguishes it from other languages."^[58]

C++ inherits most of C's syntax. The following is Bjarne Stroustrup's version of the Hello world program that uses the C++ Standard Library stream facility to write a message to standard output:^[59]^[60]^{[note 1]}

#include <iostream>
using namespace std;
int main()
{
    cout << "Hello, world!\n";
    return 0;
}

Object storage[edit]

As in C, C++ supports four types of memory management: static storage duration objects, thread storage duration objects, automatic storage duration objects, and dynamic storage duration objects.^[61]

Static storage duration objects[edit]

Static storage duration objects are created before main() is entered (see exceptions below) and destroyed in reverse order of creation after main() exits. The exact order of creation is not specified by the standard (though there are some rules defined below) to allow implementations some freedom in how to organize their implementation. More formally, objects of this type have a lifespan that "shall last for the duration of the program".^[62]

Static storage duration objects are initialized in two phases. First, "static initialization" is performed, and only after all static initialization is performed, "dynamic initialization" is performed. In static initialization, all objects are first initialized with zeros; after that, all objects that have a constant initialization phase are initialized with the constant expression (i.e. variables initialized with a literal or constexpr). Though it is not specified in the standard, the static initialization phase can be completed at compile time and saved in the data partition of the executable. Dynamic initialization involves all object initialization done via a constructor or function call (unless the function is marked with constexpr, in C++11). The dynamic initialization order is defined as the order of declaration within the compilation unit (i.e. the same file). No guarantees are provided about the order of initialization between compilation units.

Thread storage duration objects[edit]

Variables of this type are very similar to static storage duration objects. The main difference is the creation time is just prior to thread creation and destruction is done after the thread has been joined.^[63]

Automatic storage duration objects[edit]

The most common variable types in C++ are local variables inside a function or block, and temporary variables.^[64] The common feature about automatic variables is that they have a lifetime that is limited to the scope of the variable. They are created and potentially initialized at the point of declaration (see below for details) and destroyed in the reverse order of creation when the scope is left. This is implemented by allocation on the stack.

Local variables are created as the point of execution passes the declaration point. If the variable has a constructor or initializer this is used to define the initial state of the object. Local variables are destroyed when the local block or function that they are declared in is closed. C++ destructors for local variables are called at the end of the object lifetime, allowing a discipline for automatic resource management termed RAII, which is widely used in C++.

Member variables are created when the parent object is created. Array members are initialized from 0 to the last member of the array in order. Member variables are destroyed when the parent object is destroyed in the reverse order of creation. i.e. If the parent is an "automatic object" then it will be destroyed when it goes out of scope which triggers the destruction of all its members.

Temporary variables are created as the result of expression evaluation and are destroyed when the statement containing the expression has been fully evaluated (usually at the ; at the end of a statement).

Dynamic storage duration objects[edit]

These objects have a dynamic lifespan and can be created directly with a call to new and destroyed explicitly with a call to delete.^[65] C++ also supports malloc and free, from C, but these are not compatible with new and delete. Use of new returns an address to the allocated memory. The C++ Core Guidelines advise against using new directly for creating dynamic objects in favor of smart pointers through make_unique<T> for single ownership and make_shared<T> for reference-counted multiple ownership,^[66] which were introduced in C++11.

Templates[edit]

C++ templates enable generic programming. 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 "Substitution failure is not an error" (SFINAE). Templates are a powerful tool that can be used for generic programming, template metaprogramming, 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.^[67] This is in contrast to run-time generics seen in other languages (e.g., Java) where at compile-time the type is erased and a single template body is preserved.

Templates are different from macros: 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 polymorphism (see below) and generic programming.

In addition, templates are a compile-time mechanism in C++ that is Turing-complete, meaning that any computation expressible by a computer program can be computed, in some form, by a template metaprogram 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[edit]

C++ introduces object-oriented programming (OOP) features to C. It offers classes, which provide the four features commonly present in OOP (and some non-OOP) languages: abstraction, encapsulation, inheritance, and polymorphism. One distinguishing feature of C++ classes compared to classes in other programming languages is support for deterministic destructors, which in turn provide support for the Resource Acquisition is Initialization (RAII) concept.

Encapsulation

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 modular programming.

It is generally considered good practice to make all data 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.