C++ (pronounced "C plus plus") is a
high-level general-purpose programming language
In computer software, a general-purpose programming language (GPL) is a programming language for building software in a wide variety of application domains. Conversely, a domain-specific programming language is used within a specific area. For exam ...
created by Danish computer scientist
Bjarne Stroustrup
Bjarne Stroustrup (; ; born 30 December 1950) is a Danish computer scientist, most notable for the invention and development of the C++ programming language. As of July 2022, Stroustrup is a professor of Computer Science at Columbia University ...
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
Object-oriented programming (OOP) is a programming paradigm based on the concept of " objects", which can contain data and code. The data is in the form of fields (often known as attributes or ''properties''), and the code is in the form of p ...
,
generic
Generic or generics may refer to:
In business
* Generic term, a common name used for a range or class of similar things not protected by trademark
* Generic brand, a brand for a product that does not have an associated brand or trademark, other ...
, and
functional features in addition to facilities for
low-level memory
Memory is the faculty of the mind by which data or information is encoded, stored, and retrieved when needed. It is the retention of information over time for the purpose of influencing future action. If past events could not be remembered ...
manipulation. It is almost always implemented as a
compiled language, and many vendors provide
C++ compilers
C, or c, is the third letter in the Latin alphabet, used in the modern English alphabet, the alphabets of other western European languages and others worldwide. Its name in English is ''cee'' (pronounced ), plural ''cees''.
History
"C" ...
, including the
Free Software Foundation
The Free Software Foundation (FSF) is a 501(c)(3) non-profit organization founded by Richard Stallman on October 4, 1985, to support the free software movement, with the organization's preference for software being distributed under copyleft (" ...
,
LLVM
LLVM is a set of compiler and toolchain technologies that can be used to develop a front end for any programming language and a back end for any instruction set architecture. LLVM is designed around a language-independent intermediate repre ...
,
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, Washin ...
,
Intel
Intel Corporation is an American multinational corporation and technology company headquartered in Santa Clara, California. It is the world's largest semiconductor chip manufacturer by revenue, and is one of the developers of the x86 seri ...
,
Embarcadero,
Oracle, and
IBM, so it is available on many platforms.
C++ was designed with
systems programming Systems programming, or system programming, is the activity of programming computer system software. The primary distinguishing characteristic of systems programming when compared to application programming is that application programming aims to pr ...
and
embedded, resource-constrained software and large systems in mind, with
performance, 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
desktop applications,
video games
Video games, also known as computer games, are electronic games that involves interaction with a user interface or input device such as a joystick, controller, keyboard, or motion sensing device to generate visual feedback. This feedbac ...
,
servers (e.g.
e-commerce
E-commerce (electronic commerce) is the activity of electronically buying or selling of products on online services or over the Internet. E-commerce draws on technologies such as mobile commerce, electronic funds transfer, supply chain managem ...
,
web search
Web most often refers to:
* Spider web, a silken structure created by the animal
* World Wide Web or the Web, an Internet-based hypertext system
Web, WEB, or the Web may also refer to:
Computing
* WEB, a literate programming system created by ...
, or
database
In computing, a database is an organized collection of data stored and accessed electronically. Small databases can be stored on a file system, while large databases are hosted on computer clusters or cloud storage. The design of databases s ...
s), and performance-critical applications (e.g.
telephone switches
telephone exchange, telephone switch, or central office is a telecommunications system used in the public switched telephone network (PSTN) or in large enterprises. It interconnects telephone subscriber lines or virtual circuits of digital syst ...
or
space probes
Space is the boundless three-dimensional extent in which objects and events have relative position and direction. In classical physics, physical space is often conceived in three linear dimensions, although modern physicists usually conside ...
).
C++ is standardized by the
International Organization for Standardization
The International Organization for Standardization (ISO ) is an international standard development organization composed of representatives from the national standards organizations of member countries. Membership requirements are given in Art ...
(ISO), with the latest standard version ratified and published by ISO in December 2020 as
''ISO/IEC 14882:2020'' (informally known as
C++20 C20 or C-20 may refer to:
Science and technology
* Carbon-20 (C-20 or 20C), an isotope of carbon
* C20, the smallest possible fullerene (a carbon molecule)
* C20 (engineering), a mix of concrete that has a compressive strength of 20 newtons per sq ...
).
The C++ programming language was initially standardized in 1998 as ''ISO/IEC 14882:1998'', which was then amended by the
C++03
C, or c, is the third letter in the Latin alphabet, used in the modern English alphabet, the alphabets of other western European languages and others worldwide. Its name in English is ''cee'' (pronounced ), plural ''cees''.
History
"C" ...
,
C++11
C++11 is a version of the ISO/ IEC 14882 standard for the C++ programming language. C++11 replaced the prior version of the C++ standard, called C++03, and was later replaced by C++14. The name follows the tradition of naming language versions b ...
,
C++14
C++14 is a version of the ISO/IEC 14882 standard for the C++ programming language. It is intended to be a small extension over C++11, featuring mainly bug fixes and small improvements, and was replaced by C++17. Its approval was announced on Augus ...
, and
C++17 standards. The current
C++20 C20 or C-20 may refer to:
Science and technology
* Carbon-20 (C-20 or 20C), an isotope of carbon
* C20, the smallest possible fullerene (a carbon molecule)
* C20 (engineering), a mix of concrete that has a compressive strength of 20 newtons per sq ...
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
Nokia Bell Labs, originally named Bell Telephone Laboratories (1925–1984),
then AT&T Bell Laboratories (1984–1996)
and Bell Labs Innovations (1996–2007),
is an American industrial Research and development, research and scientific developm ...
since 1979 as an extension of the
C language
C (''pronounced like the letter c'') is a general-purpose computer programming language. It was created in the 1970s by Dennis Ritchie, and remains very widely used and influential. By design, C's features cleanly reflect the capabilities o ...
; he wanted an efficient and flexible language similar to C that also provided
high-level features for program organization. Since 2012, C++ has been on a three-year release schedule with
C++23 C23 or C-23 may refer to:
Vehicles
;Aircraft
* Beechcraft C23 Musketeer, an American civil utility aircraft
* Caspar C 23, a German sport aircraft
* Caudron C.23, a French bomber biplane
* Lockheed C-23 Altair, an American military transport
...
as the next planned standard.
History
![BjarneStroustrup](https://upload.wikimedia.org/wikipedia/commons/d/da/BjarneStroustrup.jpg)
In 1979,
Bjarne Stroustrup
Bjarne Stroustrup (; ; born 30 December 1950) is a Danish computer scientist, most notable for the invention and development of the C++ programming language. As of July 2022, Stroustrup is a professor of Computer Science at Columbia University ...
, a Danish
computer scientist, began work on "", 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
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
Nokia Bell Labs, originally named Bell Telephone Laboratories (1925–1984),
then AT&T Bell Laboratories (1984–1996)
and Bell Labs Innovations (1996–2007),
is an American industrial research and scientific development company owned by mult ...
, he had the problem of analyzing the
UNIX
Unix (; trademarked as UNIX) is a family of multitasking, multiuser computer operating systems that derive from the original AT&T Unix, whose development started in 1969 at the Bell Labs research center by Ken Thompson, Dennis Ritchie, an ...
kernel
Kernel may refer to:
Computing
* Kernel (operating system), the central component of most operating systems
* Kernel (image processing), a matrix used for image convolution
* Compute kernel, in GPGPU programming
* Kernel method, in machine learn ...
with respect to
distributed computing
A distributed system is a system whose components are located on different networked computers, which communicate and coordinate their actions by passing messages to one another from any system. Distributed computing is a field of computer sci ...
. Remembering his PhD experience, Stroustrup set out to enhance the
C language with
Simula-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
ALGOL 68
ALGOL 68 (short for ''Algorithmic Language 1968'') is an imperative programming language that was conceived as a successor to the ALGOL 60 programming language, designed with the goal of a much wider scope of application and more rigorously d ...
,
Ada
Ada may refer to:
Places
Africa
* Ada Foah, a town in Ghana
* Ada (Ghana parliament constituency)
* Ada, Osun, a town in Nigeria
Asia
* Ada, Urmia, a village in West Azerbaijan Province, Iran
* Ada, Karaman, a village in Karaman Province, ...
,
CLU and
ML.
Initially, Stroustrup's "C with Classes" added features to the C compiler, Cpre, including
classes,
derived classes,
strong typing,
inlining
In computing, inline expansion, or inlining, is a manual or compiler optimization that replaces a function call site with the body of the called function. Inline expansion is similar to macro expansion, but occurs during compilation, without cha ...
and
default argument
In computer programming, a default argument is an argument to a function that a programmer is not required to specify.
In most programming languages, functions may take one or more arguments. Usually, each argument must be specified in full (this ...
s.
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 function
In object-oriented programming, in languages such as C++, and Object Pascal, a virtual function or virtual method is an inheritable and overridable function or method for which dynamic dispatch is facilitated. This concept is an important p ...
s, function name and
operator overloading
In computer programming, operator overloading, sometimes termed ''operator ad hoc polymorphism'', is a specific case of polymorphism, where different operators have different implementations depending on their arguments. Operator overloading i ...
,
reference
Reference is a relationship between objects in which one object designates, or acts as a means by which to connect to or link to, another object. The first object in this relation is said to ''refer to'' the second object. It is called a '' name'' ...
s, 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
Cfront was the original compiler for C++ (then known as " C with Classes") from around 1983, which converted C++ to C; developed by Bjarne Stroustrup at AT&T Bell Labs. The preprocessor did not understand all of the language and much of the code wa ...
.
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
Malcolm Douglas McIlroy (born 1932) is a mathematician, engineer, and programmer. As of 2019 he is an Adjunct Professor of Computer Science at Dartmouth College.
McIlroy is best known for having originally proposed Unix pipelines and developed s ...
(who had previously suggested
Unix pipes
In Unix-like computer operating systems, a pipeline is a mechanism for inter-process communication using message passing. A pipeline is a set of processes chained together by their standard streams, so that the output text of each process (''stdo ...
).
In 1985, the first edition of ''
The C++ Programming Language
''The C++ Programming Language'' is a computer programming book first published in October 1985. It was the first book to describe the C++ programming language, written by the language's creator, Bjarne Stroustrup. In the absence of an official ...
'' 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,
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
template
Template may refer to:
Tools
* Die (manufacturing), used to cut or shape material
* Mold, in a molding process
* Stencil, a pattern or overlay used in graphic arts (drawing, painting, etc.) and sewing to replicate letters, shapes or designs
...
s,
exceptions,
namespaces
In computing, a namespace is a set of signs (''names'') that are used to identify and refer to objects of various kinds. A namespace ensures that all of a given set of objects have unique names so that they can be easily identified.
Namespaces ...
, new
cast
Cast may refer to:
Music
* Cast (band), an English alternative rock band
* Cast (Mexican band), a progressive Mexican rock band
* The Cast, a Scottish musical duo: Mairi Campbell and Dave Francis
* ''Cast'', a 2012 album by Trespassers William
...
s, and a
Boolean type
In computer science, the Boolean (sometimes shortened to Bool) is a data type that has one of two possible values (usually denoted ''true'' and ''false'') which is intended to represent the two truth values of logic and Boolean algebra. It is named ...
.
In 1998, C++98 was released, standardizing the language, and a minor update (
C++03
C, or c, is the third letter in the Latin alphabet, used in the modern English alphabet, the alphabets of other western European languages and others worldwide. Its name in English is ''cee'' (pronounced ), plural ''cees''.
History
"C" ...
) was released in 2003.
After C++98, C++ evolved relatively slowly until, in 2011, the
C++11
C++11 is a version of the ISO/ IEC 14882 standard for the C++ programming language. C++11 replaced the prior version of the C++ standard, called C++03, and was later replaced by C++14. The name follows the tradition of naming language versions b ...
standard was released, adding numerous new features, enlarging the standard library further, and providing more facilities to C++ programmers. After a minor
C++14
C++14 is a version of the ISO/IEC 14882 standard for the C++ programming language. It is intended to be a small extension over C++11, featuring mainly bug fixes and small improvements, and was replaced by C++17. Its approval was announced on Augus ...
update released in December 2014, various new additions were introduced in
C++17.
After becoming finalized in February 2020, a draft of the C++20 standard was approved on 4 September 2020 and officially published on 15 December 2020.
On January 3, 2018, Stroustrup was announced as the 2018 winner of the
Charles Stark Draper Prize
The U.S. National Academy of Engineering annually awards the Draper Prize, which is given for the advancement of engineering and the education of the public about engineering. It is one of three prizes that constitute the "Nobel Prizes of Enginee ...
for Engineering, "for conceptualizing and developing the C++ programming language".
C++ ranked third on the
TIOBE index
The TIOBE programming community index is a measure of popularity of programming languages, created and maintained by TIOBE Software BV, based in Eindhoven, the Netherlands. TIOBE stands for ''The Importance of Being Earnest'', the title of an 1 ...
, surpassing
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 mos ...
for the first time in the history of the index. It ranks 3rd, after
Python
Python may refer to:
Snakes
* Pythonidae, a family of nonvenomous snakes found in Africa, Asia, and Australia
** ''Python'' (genus), a genus of Pythonidae found in Africa and Asia
* Python (mythology), a mythical serpent
Computing
* Python (pro ...
and
C.
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
tongue-in-cheek
The idiom tongue-in-cheek refers to a humorous or sarcastic statement expressed in a serious manner.
History
The phrase originally expressed contempt, but by 1842 had acquired its modern meaning. Early users of the phrase include Sir Walter Scot ...
spirit. The name comes from C's
++ operator (which
increments the
value of a
variable
Variable may refer to:
* Variable (computer science), a symbolic name associated with a value and whose associated value may be changed
* Variable (mathematics), a symbol that represents a quantity in a mathematical expression, as used in many ...
) and a common
naming convention
A naming convention is a convention (generally agreed scheme) for naming things. Conventions differ in their intents, which may include to:
* Allow useful information to be deduced from the names based on regularities. For instance, in Manhatta ...
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"
before acquiring its final name.
Philosophy
Throughout C++'s life, its development and evolution has been guided by a set of principles:
* 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
In computer programming, a type system is a logical system comprising a set of rules that assigns a property called a type to every "term" (a word, phrase, or other set of symbols). Usually the terms are various constructs of a computer progr ...
(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 language
A programming language is a system of notation for writing computer programs. Most programming languages are text-based formal languages, but they may also be graphical. They are a kind of computer language.
The description of a programming ...
s, 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
C++ is standardized by an
ISO
ISO is the most common abbreviation for the International Organization for Standardization.
ISO or Iso may also refer to: Business and finance
* Iso (supermarket), a chain of Danish supermarkets incorporated into the SuperBest chain in 2007
* Iso ...
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 C23 or C-23 may refer to:
Vehicles
;Aircraft
* Beechcraft C23 Musketeer, an American civil utility aircraft
* Caspar C 23, a German sport aircraft
* Caudron C.23, a French bomber biplane
* Lockheed C-23 Altair, an American military transport
...
.
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.
C++11
C++11 is a version of the ISO/ IEC 14882 standard for the C++ programming language. C++11 replaced the prior version of the C++ standard, called C++03, and was later replaced by C++14. The name follows the tradition of naming language versions b ...
(14882:2011) included many additions to both the core language and the standard library.
In 2014,
C++14
C++14 is a version of the ISO/IEC 14882 standard for the C++ programming language. It is intended to be a small extension over C++11, featuring mainly bug fixes and small improvements, and was replaced by C++17. Its approval was announced on Augus ...
(also known as C++1y) was released as a small extension to
C++11
C++11 is a version of the ISO/ IEC 14882 standard for the C++ programming language. C++11 replaced the prior version of the C++ standard, called C++03, and was later replaced by C++14. The name follows the tradition of naming language versions b ...
, featuring mainly bug fixes and small improvements.
The Draft International Standard ballot procedures completed in mid-August 2014.
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.
As part of the standardization process, ISO also publishes
technical reports and specifications:
* ISO/IEC TR 18015:2006 on the use of C++ in embedded systems and on performance implications of C++ language and library features,
* ISO/IEC TR 19768:2007 (also known as the
C++ Technical Report 1) on library extensions mostly integrated into
C++11
C++11 is a version of the ISO/ IEC 14882 standard for the C++ programming language. C++11 replaced the prior version of the C++ standard, called C++03, and was later replaced by C++14. The name follows the tradition of naming language versions b ...
,
* ISO/IEC TR 29124:2010 on special mathematical functions, integrated into
C++17
* ISO/IEC TR 24733:2011 on
decimal floating-point
Decimal floating-point (DFP) arithmetic refers to both a representation and operations on decimal floating-point numbers. Working directly with decimal (base-10) fractions can avoid the rounding errors that otherwise typically occur when convert ...
arithmetic,
* ISO/IEC TS 18822:2015 on the standard filesystem library, integrated into
C++17
* ISO/IEC TS 19570:2015 on
parallel
Parallel is a geometric term of location which may refer to:
Computing
* Parallel algorithm
* Parallel computing
* Parallel metaheuristic
* Parallel (software), a UNIX utility for running programs in parallel
* Parallel Sysplex, a cluster of ...
versions of the standard library algorithms, integrated into
C++17
* ISO/IEC TS 19841:2015 on software
transactional memory In computer science and engineering, transactional memory attempts to simplify concurrent programming by allowing a group of load and store instructions to execute in an atomic way. It is a concurrency control mechanism analogous to database transa ...
,
* ISO/IEC TS 19568:2015 on a new set of library extensions, some of which are already integrated into
C++17,
* ISO/IEC TS 19217:2015 on the C++
concepts
Concepts are defined as abstract ideas. They are understood to be the fundamental building blocks of the concept behind principles, thoughts and beliefs.
They play an important role in all aspects of cognition. As such, concepts are studied by s ...
, integrated into
C++20 C20 or C-20 may refer to:
Science and technology
* Carbon-20 (C-20 or 20C), an isotope of carbon
* C20, the smallest possible fullerene (a carbon molecule)
* C20 (engineering), a mix of concrete that has a compressive strength of 20 newtons per sq ...
* ISO/IEC TS 19571:2016 on the library extensions for concurrency, some of which are already integrated into
C++20 C20 or C-20 may refer to:
Science and technology
* Carbon-20 (C-20 or 20C), an isotope of carbon
* C20, the smallest possible fullerene (a carbon molecule)
* C20 (engineering), a mix of concrete that has a compressive strength of 20 newtons per sq ...
* ISO/IEC TS 19568:2017 on a new set of general-purpose library extensions
* ISO/IEC TS 21425:2017 on the library extensions for ranges, integrated into
C++20 C20 or C-20 may refer to:
Science and technology
* Carbon-20 (C-20 or 20C), an isotope of carbon
* C20, the smallest possible fullerene (a carbon molecule)
* C20 (engineering), a mix of concrete that has a compressive strength of 20 newtons per sq ...
* ISO/IEC TS 22277:2017 on coroutines, integrated into
C++20 C20 or C-20 may refer to:
Science and technology
* Carbon-20 (C-20 or 20C), an isotope of carbon
* C20, the smallest possible fullerene (a carbon molecule)
* C20 (engineering), a mix of concrete that has a compressive strength of 20 newtons per sq ...
* ISO/IEC TS 19216:2018 on the networking library
* ISO/IEC TS 21544:2018 on modules, integrated into
C++20 C20 or C-20 may refer to:
Science and technology
* Carbon-20 (C-20 or 20C), an isotope of carbon
* C20, the smallest possible fullerene (a carbon molecule)
* C20 (engineering), a mix of concrete that has a compressive strength of 20 newtons per sq ...
* ISO/IEC TS 19570:2018 on a new set of library extensions for parallelism
* ISO/IEC TS 23619:2021 on a new extensions for reflection
More technical specifications are in development and pending approval, including new set of concurrency extensions.
Language
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
esignedfor building and using efficient and elegant abstractions";
and "offering both hardware access and abstraction is the basis of C++. Doing it efficiently is what distinguishes it from other languages."
C++ inherits most of
C's syntax. The following is Bjarne Stroustrup's version of the
Hello world program
''Hello'' is a salutation or greeting in the English language. It is first attested in writing from 1826. Early uses
''Hello'', with that spelling, was used in publications in the U.S. as early as the 18 October 1826 edition of the '' Norwich ...
that uses the
C++ Standard Library
The C standard library or libc is the standard library for the C programming language, as specified in the ISO C standard. ISO/IEC (2018). '' ISO/IEC 9899:2018(E): Programming Languages - C §7'' Starting from the original ANSI C standard, it was ...
stream facility to write a message to
standard output
In computer programming, standard streams are interconnected input and output communication channels between a computer program and its environment when it begins execution. The three input/output (I/O) connections are called standard input (stdin ...
:
[This code is copied directly from Bjarne Stroustrup's errata page (p. 633). He addresses the use of ]'\n'
rather than std::endl
. Also se
Can I write "void main()"?
for an explanation of the implicit return 0;
in the main
function. This implicit return is ''not'' available in other functions.
#include
int main()
Object storage
As in C, C++ supports four types of
memory management
Memory management is a form of resource management applied to computer memory. The essential requirement of memory management is to provide ways to dynamically allocate portions of memory to programs at their request, and free it for reuse when ...
: static storage duration objects, thread storage duration objects, automatic storage duration objects, and dynamic storage duration objects.
ISO
ISO is the most common abbreviation for the International Organization for Standardization.
ISO or Iso may also refer to: Business and finance
* Iso (supermarket), a chain of Danish supermarkets incorporated into the SuperBest chain in 2007
* Iso ...
/ IEC.
Programming Languages – C++11 Draft (n3797)
§3.7 Storage duration asic.stc'
Static storage duration objects
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".
ISO
ISO is the most common abbreviation for the International Organization for Standardization.
ISO or Iso may also refer to: Business and finance
* Iso (supermarket), a chain of Danish supermarkets incorporated into the SuperBest chain in 2007
* Iso ...
/ IEC.
Programming Languages – C++11 Draft (n3797)
§3.7.1 Static Storage duration asic.stc.static'
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
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.
ISO
ISO is the most common abbreviation for the International Organization for Standardization.
ISO or Iso may also refer to: Business and finance
* Iso (supermarket), a chain of Danish supermarkets incorporated into the SuperBest chain in 2007
* Iso ...
/ IEC.
Programming Languages – C++11 Draft (n3797)
§3.7.2 Thread Storage duration asic.stc.thread'
Automatic storage duration objects
The most common variable types in C++ are local variables inside a function or block, and temporary variables.
ISO
ISO is the most common abbreviation for the International Organization for Standardization.
ISO or Iso may also refer to: Business and finance
* Iso (supermarket), a chain of Danish supermarkets incorporated into the SuperBest chain in 2007
* Iso ...
/ IEC.
Programming Languages – C++11 Draft (n3797)
§3.7.3 Automatic Storage duration asic.stc.auto' 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
These objects have a dynamic lifespan and can be created directly with a call to and destroyed explicitly with a call to .
ISO
ISO is the most common abbreviation for the International Organization for Standardization.
ISO or Iso may also refer to: Business and finance
* Iso (supermarket), a chain of Danish supermarkets incorporated into the SuperBest chain in 2007
* Iso ...
/ IEC.
Programming Languages – C++11 Draft (n3797)
§3.7.4 Dynamic Storage duration basic.stc.dynamic">/nowiki>basic.stc.dynamic/nowiki>'' C++ also supports
malloc
and
free
, from C, but these are not compatible with and . Use of returns an address to the allocated memory. The C++ Core Guidelines advise against using directly for creating dynamic objects in favor of smart pointers through for single ownership and for reference-counted multiple ownership, which were introduced in C++11.
Templates
C++ templates
C, or c, is the third Letter (alphabet), letter in the Latin alphabet, used in the English alphabet, modern English alphabet, the alphabets of other western European languages and others worldwide. Its name in English is English alphabet#Le ...
enable
generic programming
Generic programming is a style of computer programming in which algorithms are written in terms of types ''to-be-specified-later'' that are then ''instantiated'' when needed for specific types provided as parameters. This approach, pioneered b ...
. 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
Generic programming is a style of computer programming in which algorithms are written in terms of types ''to-be-specified-later'' that are then ''instantiated'' when needed for specific types provided as parameters. This approach, pioneered b ...
,
template metaprogramming
Template metaprogramming (TMP) is a metaprogramming technique in which templates are used by a compiler to generate temporary source code, which is merged by the compiler with the rest of the source code and then compiled. The output of these t ...
, 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.,
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 mos ...
) 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
Generic programming is a style of computer programming in which algorithms are written in terms of types ''to-be-specified-later'' that are then ''instantiated'' when needed for specific types provided as parameters. This approach, pioneered b ...
.
In addition, templates are a compile-time mechanism in C++ that is
Turing-complete
In computability theory, a system of data-manipulation rules (such as a computer's instruction set, a programming language, or a cellular automaton) is said to be Turing-complete or computationally universal if it can be used to simulate any ...
, 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
C++ introduces
object-oriented programming
Object-oriented programming (OOP) is a programming paradigm based on the concept of "objects", which can contain data and code. The data is in the form of fields (often known as attributes or ''properties''), and the code is in the form of ...
(OOP) features to C. It offers
classes, which provide the four features commonly present in OOP (and some non-OOP) languages:
abstraction,
encapsulation,
inheritance
Inheritance is the practice of receiving private property, titles, debts, entitlements, privileges, rights, and obligations upon the death of an individual. The rules of inheritance differ among societies and have changed over time. Officia ...
, 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
Modular programming is a software design technique that emphasizes separating the functionality of a Computer program, program into independent, interchangeable modules, such that each contains everything necessary to execute only one aspect of th ...
.
It is generally considered good practice to make all
data
In the pursuit of knowledge, data (; ) is a collection of discrete Value_(semiotics), values that convey information, describing quantity, qualitative property, quality, fact, statistics, other basic units of meaning, or simply sequences of sy ...
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
Inheritance
Inheritance is the practice of receiving private property, titles, debts, entitlements, privileges, rights, and obligations upon the death of an individual. The rules of inheritance differ among societies and have changed over time. Officia ...
allows one data type to acquire properties of other data types. Inheritance from a
base class
In object-oriented programming, inheritance is the mechanism of basing an object or class upon another object ( prototype-based inheritance) or class ( class-based inheritance), retaining similar implementation. Also defined as deriving new classe ...
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
Virtual inheritance is a C++ technique that ensures only one copy of a base classs member variables are inherited by grandchild derived classes. Without virtual inheritance, if two classes B and C inherit from a class A, and a class D inherits fr ...
. 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.
Multiple inheritance
Multiple inheritance is a feature of some object-oriented computer programming languages in which an object or class can inherit features from more than one parent object or parent class. It is distinct from single inheritance, where an object or ...
is a C++ feature 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
C# or
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 mos ...
, accomplish something similar (although more limited) by allowing inheritance of multiple
interfaces 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
abstract base class 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
dominance.
Operators and operator overloading
C++ provides more than 35 operators, covering basic arithmetic, bit manipulation, indirection, comparisons, logical operations and others. Almost all operators can be
overloaded 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
smart pointers. 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
short-circuit evaluation
A short circuit (sometimes abbreviated to short or s/c) is an electrical circuit that allows a current to travel along an unintended path with no or very low electrical impedance. This results in an excessive current flowing through the circuit. ...
property.
Polymorphism
Polymorphism enables one common interface for many implementations, and for objects to act differently under different circumstances.
C++ supports several kinds of ''static'' (resolved at
compile-time
In computer science, compile time (or compile-time) describes the time window during which a computer program is compiled.
The term is used as an adjective to describe concepts related to the context of program compilation, as opposed to concept ...
) and ''dynamic'' (resolved at
run-time)
polymorphisms, supported by the language features described above.
Compile-time polymorphism
In computing, static dispatch is a form of polymorphism fully resolved during compile time. It is a form of ''method dispatch,'' which describes how a language or environment will select which implementation of a method or function to use.
Ex ...
does not allow for certain run-time decisions, while
runtime polymorphism
In computer science, dynamic dispatch is the process of selecting which implementation of a polymorphic operation (method or function) to call at run time. It is commonly employed in, and considered a prime characteristic of, object-oriented ...
typically incurs a performance penalty.
Static polymorphism
Function overloading
In some programming languages, function overloading or method overloading is the ability to create multiple functions of the same name with different implementations. Calls to an overloaded function will run a specific implementation of that f ...
allows programs to declare multiple functions having the same name but with different arguments (i.e.
''ad hoc'' polymorphism). The functions are distinguished by the number or types of their
formal parameters. 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 differing return types would result in a compile-time error message.
When declaring a function, a programmer can specify for one or more parameters a
default value. 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.
Templates
Template may refer to:
Tools
* Die (manufacturing), used to cut or shape material
* Mold, in a molding process
* Stencil, a pattern or overlay used in graphic arts (drawing, painting, etc.) and sewing to replicate letters, shapes or designs
Co ...
in C++ provide a sophisticated mechanism for writing generic, polymorphic code (i.e.
parametric polymorphism
In programming languages and type theory, parametric polymorphism allows a single piece of code to be given a "generic" type, using variables in place of actual types, and then instantiated with particular types as needed. Parametrically polymorph ...
). In particular, through the
curiously recurring template pattern
The curiously recurring template pattern (CRTP) is an idiom, originally in C++, in which a class X derives from a class template instantiation using X itself as a template argument. More generally it is known as F-bound polymorphism, and it is a ...
, 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
Turing-complete
In computability theory, a system of data-manipulation rules (such as a computer's instruction set, a programming language, or a cellular automaton) is said to be Turing-complete or computationally universal if it can be used to simulate any ...
, they can also be used to let the compiler resolve recursive conditionals and generate substantial programs through
template metaprogramming
Template metaprogramming (TMP) is a metaprogramming technique in which templates are used by a compiler to generate temporary source code, which is merged by the compiler with the rest of the source code and then compiled. The output of these t ...
. Contrary to some opinion, template code will not generate a bulk code after compilation with the proper compiler settings.
Dynamic polymorphism
=Inheritance
=
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
dynamic_cast 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
static_cast, as ancestral classes are specified in the derived class's interface, visible to all callers.)
dynamic_cast relies on
run-time type information In computer programming, run-time type information or run-time type identification (RTTI) is a feature of some programming languages (such as C++, Object Pascal, and Ada) that exposes information about an object's data type at runtime. Run-time typ ...
(RTTI), metadata in the program that enables differentiating types and their relationships. If a
dynamic_cast 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
static_cast, bypassing RTTI and the safe runtime type-checking of
dynamic_cast, 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
overrides 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
dynamic dispatch
In computer science, dynamic dispatch is the process of selecting which implementation of a polymorphic operation (method or function) to call at run time. It is commonly employed in, and considered a prime characteristic of, object-oriented ...
.
Virtual member functions 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
virtual function tables. If the object type is known, this may be bypassed by prepending a
fully qualified class name 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. An inexact rule based on practical experience states that 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
anonymous functions, also known as
lambda expressions Lambda expression may refer to:
*Lambda expression in computer programming, also called an anonymous function, is a defined function not bound to an identifier.
* Lambda expression in lambda calculus, a formal system in mathematical logic and ...
, with the following form:
apture Apture was a service that allowed publishers and bloggers to link and incorporate multimedia into a dynamic layer above their pages.
Apture was used by several large organizations and publishers including ''The Washington Post'', ''The Economist'' ...
parameters) -> return_type
Since C++20, you can write template parameters on a lambda without the keyword :
apture Apture was a service that allowed publishers and bloggers to link and incorporate multimedia into a dynamic layer above their pages.
Apture was used by several large organizations and publishers including ''The Washington Post'', ''The Economist'' ...
template_parameters>(parameters) -> return_type
If the lambda takes no parameters, and no return type or other specifiers are used, the () can be omitted, that is,
apture Apture was a service that allowed publishers and bloggers to link and incorporate multimedia into a dynamic layer above their pages.
Apture was used by several large organizations and publishers including ''The Washington Post'', ''The Economist'' ...
The return type of a lambda expression can be automatically inferred, if possible, e.g.:
[](int x, int y) // inferred
[](int x, int y) -> int // explicit
The
apture Apture was a service that allowed publishers and bloggers to link and incorporate multimedia into a dynamic layer above their pages.
Apture was used by several large organizations and publishers including ''The Washington Post'', ''The Economist'' ...
/syntaxhighlight> list supports the definition of closures. Such lambda expressions are defined in the standard as syntactic sugar
In computer science, syntactic sugar is syntax within a programming language that is designed to make things easier to read or to express. It makes the language "sweeter" for human use: things can be expressed more clearly, more concisely, or in an ...
for an unnamed function object
In computer programming, a function object is a construct allowing an object to be invoked or called as if it were an ordinary function, usually with the same syntax (a function parameter that can also be a function). Function objects are often c ...
.
Exception handling
Exception handling is used to communicate the existence of a runtime problem or error from where it was detected to where the issue can be handled. It permits this to be done in a uniform manner and separately from the main code, while detecting all errors. Should an error occur, an exception is thrown (raised), which is then caught by the nearest suitable exception handler. The exception causes the current scope to be exited, and also each outer scope (propagation) until a suitable handler is found, calling in turn the destructors of any objects in these exited scopes. At the same time, an exception is presented as an object carrying the data about the detected problem.
Some C++ style guides, such as Google's, LLVM's, and Qt's forbid the usage of exceptions.
The exception-causing code is placed inside a try block. The exceptions are handled in separate catch blocks (the handlers); each try block can have multiple exception handlers, as it is visible in the example below.
#include
#include
#include
int main()
It is also possible to raise exceptions purposefully, using the throw keyword; these exceptions are handled in the usual way. In some cases, exceptions cannot be used due to technical reasons. One such example is a critical component of an embedded system, where every operation must be guaranteed to complete within a specified amount of time. This cannot be determined with exceptions as no tools exist to determine the maximum time required for an exception to be handled.
Unlike signal handling, in which the handling function is called from the point of failure, exception handling exits the current scope before the catch block is entered, which may be located in the current function or any of the previous function calls currently on the stack.
Enumerated types
Standard library
; it includes aggregate types ( vectors, lists, maps, sets, queues, stacks, arrays, tuples), algorithm
In mathematics and computer science, an algorithm () is a finite sequence of rigorous instructions, typically used to solve a class of specific problems or to perform a computation. Algorithms are used as specifications for performing ...
s (find, for_each, binary_search
In computer science, binary search, also known as half-interval search, logarithmic search, or binary chop, is a search algorithm that finds the position of a target value within a sorted array. Binary search compares the target value to the ...
, random_shuffle, etc.), input/output facilities ( iostream, for reading from and writing to the console and files), filesystem library, localisation support, smart pointers for automatic memory management, regular expression
A regular expression (shortened as regex or regexp; sometimes referred to as rational expression) is a sequence of characters that specifies a search pattern in text. Usually such patterns are used by string-searching algorithms for "find" ...
support, multi-threading library, atomics support (allowing a variable to be read or written to by at most one thread at a time without any external synchronisation), time utilities (measurement, getting current time, etc.), a system for converting error reporting that doesn't use C++ exceptions into C++ exceptions, a random number generator
Random number generation is a process by which, often by means of a random number generator (RNG), a sequence of numbers or symbols that cannot be reasonably predicted better than by random chance is generated. This means that the particular outc ...
and a slightly modified version of the C standard library (to make it comply with the C++ type system).
A large part of the C++ library is based on the Standard Template Library
The Standard Template Library (STL) is a software library originally designed by Alexander Stepanov for the C++ programming language that influenced many parts of the C++ Standard Library. It provides four components called ''algorithms'', '' ...
(STL). Useful tools provided by the STL include container
A container is any receptacle or enclosure for holding a product used in storage, packaging, and transportation, including shipping.
Things kept inside of a container are protected on several sides by being inside of its structure. The term ...
s as the collections of objects (such as vector
Vector most often refers to:
*Euclidean vector, a quantity with a magnitude and a direction
*Vector (epidemiology), an agent that carries and transmits an infectious pathogen into another living organism
Vector may also refer to:
Mathematic ...
s and lists), iterator
In computer programming, an iterator is an object that enables a programmer to traverse a container, particularly lists. Various types of iterators are often provided via a container's interface. Though the interface and semantics of a given iterat ...
s that provide array-like access to containers, and algorithm
In mathematics and computer science, an algorithm () is a finite sequence of rigorous instructions, typically used to solve a class of specific problems or to perform a computation. Algorithms are used as specifications for performing ...
s that perform operations such as searching and sorting.
Furthermore, (multi)maps (associative array
In computer science, an associative array, map, symbol table, or dictionary is an abstract data type that stores a collection of (key, value) pairs, such that each possible key appears at most once in the collection. In mathematical terms an ...
s) and (multi)sets are provided, all of which export compatible interfaces. Therefore, using templates it is possible to write generic algorithms that work with any container or on any sequence defined by iterators. As in C, the feature
Feature may refer to:
Computing
* Feature (CAD), could be a hole, pocket, or notch
* Feature (computer vision), could be an edge, corner or blob
* Feature (software design) is an intentional distinguishing characteristic of a software item ...
s of the library
A library is a collection of materials, books or media that are accessible for use and not just for display purposes. A library provides physical (hard copies) or digital access (soft copies) materials, and may be a physical location or a vir ...
are accessed by using the #include directive to include a standard header. The C++ Standard Library
The C standard library or libc is the standard library for the C programming language, as specified in the ISO C standard. ISO/IEC (2018). '' ISO/IEC 9899:2018(E): Programming Languages - C §7'' Starting from the original ANSI C standard, it was ...
provides 105 standard headers, of which 27 are deprecated.
The standard incorporates the STL that was originally designed by Alexander Stepanov
Alexander Alexandrovich Stepanov (russian: Алекса́ндр Алекса́ндрович Степа́нов; born November 16, 1950, Moscow) is a Russian-American computer programmer, best known as an advocate of generic programming and as th ...
, who experimented with generic algorithms and containers for many years. When he started with C++, he finally found a language where it was possible to create generic algorithms (e.g., STL sort) that perform even better than, for example, the C standard library qsort, thanks to C++ features like using inlining and compile-time binding instead of function pointers. The standard does not refer to it as "STL", as it is merely a part of the standard library, but the term is still widely used to distinguish it from the rest of the standard library (input/output streams, internationalization, diagnostics, the C library subset, etc.).
Most C++ compilers, and all major ones, provide a standards-conforming implementation of the C++ standard library.
C++ Core Guidelines
The C++ Core Guidelines are an initiative led by Bjarne Stroustrup, the inventor of C++, and Herb Sutter, the convener and chair of the C++ ISO Working Group, to help programmers write 'Modern C++' by using best practices for the language standards C++11 and newer, and to help developers of compilers and static checking tools to create rules for catching bad programming practices.
The main aim is to efficiently and consistently write type and resource safe C++.
The Core Guidelines were announced in the opening keynote at CPPCon 2015.
The Guidelines are accompanied by the Guideline Support Library (GSL), a header only library of types and functions to implement the Core Guidelines and static checker tools for enforcing Guideline rules.
Compatibility
To give compiler vendors greater freedom, the C++ standards committee decided not to dictate the implementation of name mangling
In compiler construction, name mangling (also called name decoration) is a technique used to solve various problems caused by the need to resolve unique names for programming entities in many modern programming languages.
It provides a way of e ...
, exception handling
In computing and computer programming, exception handling is the process of responding to the occurrence of ''exceptions'' – anomalous or exceptional conditions requiring special processing – during the execution of a program. In general, an ...
, and other implementation-specific features. The downside of this decision is that object code
In computing, object code or object module is the product of a compiler
In computing, a compiler is a computer program that translates computer code written in one programming language (the ''source'' language) into another language (the ...
produced by different compiler
In computing, a compiler is a computer program that translates computer code written in one programming language (the ''source'' language) into another language (the ''target'' language). The name "compiler" is primarily used for programs tha ...
s is expected to be incompatible. There were, however, attempts to standardize compilers for particular machines or operating system
An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs.
Time-sharing operating systems schedule tasks for efficient use of the system and may also i ...
s (for example C++ ABI), though they seem to be largely abandoned now.
With C
C++ is often considered to be a superset of C but this is not strictly true. Most C code can easily be made to compile correctly in C++ but there are a few differences that cause some valid C code to be invalid or behave differently in C++. For example, C allows implicit conversion from void* to other pointer types but C++ does not (for type safety reasons). Also, C++ defines many new keywords, such as new and class, which may be used as identifiers (for example, variable names) in a C program.
Some incompatibilities have been removed by the 1999 revision of the C standard (C99
C99 (previously known as C9X) is an informal name for ISO/IEC 9899:1999, a past version of the C programming language standard. It extends the previous version ( C90) with new features for the language and the standard library, and helps impl ...
), which now supports C++ features such as line comments (//) and declarations mixed with code. On the other hand, C99 introduced a number of new features that C++ did not support that were incompatible or redundant in C++, such as variable-length array In computer programming, a variable-length array (VLA), also called variable-sized or runtime-sized, is an array data structure whose length is determined at run time (instead of at compile time).
In C, the VLA is said to have a variably modified t ...
s, native complex-number types (however, the std::complex class in the C++ standard library provides similar functionality, although not code-compatible), designated initializers, compound literals, and the restrict keyword. Some of the C99-introduced features were included in the subsequent version of the C++ standard, C++11
C++11 is a version of the ISO/ IEC 14882 standard for the C++ programming language. C++11 replaced the prior version of the C++ standard, called C++03, and was later replaced by C++14. The name follows the tradition of naming language versions b ...
(out of those which were not redundant). However, the C++11 standard introduces new incompatibilities, such as disallowing assignment of a string literal to a character pointer, which remains valid C.
To intermix C and C++ code, any function declaration or definition that is to be called from/used both in C and C++ must be declared with C linkage by placing it within an extern "C" block. Such a function may not rely on features depending on name mangling
In compiler construction, name mangling (also called name decoration) is a technique used to solve various problems caused by the need to resolve unique names for programming entities in many modern programming languages.
It provides a way of e ...
(i.e., function overloading).
Criticism
Despite its widespread adoption, some notable programmers have criticized the C++ language, including Linus Torvalds
Linus Benedict Torvalds ( , ; born 28 December 1969) is a Finnish software engineer who is the creator and, historically, the lead developer of the Linux kernel, used by Linux distributions and other operating systems such as Android. He also ...
, Richard Stallman
Richard Matthew Stallman (; born March 16, 1953), also known by his initials, rms, is an American free software movement activist and programmer. He campaigns for software to be distributed in such a manner that its users have the freedom to ...
, Joshua Bloch
Joshua J. Bloch (born August 28, 1961) is an American software engineer and a technology author, formerly employed at Sun Microsystems and Google. He led the design and implementation of numerous Java platform features, including the Java Collect ...
, Ken Thompson
Kenneth Lane Thompson (born February 4, 1943) is an American pioneer of computer science. Thompson worked at Bell Labs for most of his career where he designed and implemented the original Unix operating system. He also invented the B programmi ...
and Donald Knuth
Donald Ervin Knuth ( ; born January 10, 1938) is an American computer scientist, mathematician, and professor emeritus at Stanford University. He is the 1974 recipient of the ACM Turing Award, informally considered the Nobel Prize of computer sc ...
.
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 a subset of C++, thus eschewing the readability benefits of common style and idioms. As expressed by Joshua Bloch
Joshua J. Bloch (born August 28, 1961) is an American software engineer and a technology author, formerly employed at Sun Microsystems and Google. He led the design and implementation of numerous Java platform features, including the Java Collect ...
: 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.
Donald Knuth
Donald Ervin Knuth ( ; born January 10, 1938) is an American computer scientist, mathematician, and professor emeritus at Stanford University. He is the 1974 recipient of the ACM Turing Award, informally considered the Nobel Prize of computer sc ...
(1993, commenting on pre-standardized C++), who said of Edsger Dijkstra
Edsger Wybe Dijkstra ( ; ; 11 May 1930 – 6 August 2002) was a Dutch computer scientist, programmer, software engineer, systems scientist, and science essayist. He received the 1972 Turing Award for fundamental contributions to developing progra ...
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.
Ken Thompson
Kenneth Lane Thompson (born February 4, 1943) is an American pioneer of computer science. Thompson worked at Bell Labs for most of his career where he designed and implemented the original Unix operating system. He also invented the B programmi ...
, 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 built by a committee.
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 Brian Kernighan
Brian Wilson Kernighan (; born 1942) is a Canadian computer scientist.
He worked at Bell Labs and contributed to the development of Unix alongside Unix creators Ken Thompson and Dennis Ritchie. Kernighan's name became widely known through co- ...
, 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. 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 reflection Reflection or reflexion may refer to:
Science and technology
* Reflection (physics), a common wave phenomenon
** Specular reflection, reflection from a smooth surface
*** Mirror image, a reflection in a mirror or in water
** Signal reflection, in ...
or garbage collection
Waste collection is a part of the process of waste management. It is the transfer of solid waste from the point of use and disposal to the point of treatment or landfill. Waste collection also includes the curbside collection of recyclabl ...
, long compilation times, perceived feature creep
Feature creep is the excessive ongoing expansion or addition of new features in a product, especially in computer software, video games and consumer and business electronics. These extra features go beyond the basic function of the product and ...
, and verbose error messages, particularly from template metaprogramming.
See also
* Comparison of programming languages
Programming languages are used for controlling the behavior of a machine (often a computer). Like natural languages, programming languages follow the rules for syntax and semantics.
There are thousands of programming languages and new ones are c ...
* List of C++ compilers
* Outline of C++
* :C++ libraries
Footnotes
References
Further reading
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External links
JTC1/SC22/WG21
– the ISO/IEC C++ Standard Working Group
Standard C++ Foundation
– a non-profit organization that promotes the use and understanding of standard C++. Bjarne Stroustrup
Bjarne Stroustrup (; ; born 30 December 1950) is a Danish computer scientist, most notable for the invention and development of the C++ programming language. As of July 2022, Stroustrup is a professor of Computer Science at Columbia University ...
is a director of the organization.
{{DEFAULTSORT:C
Algol programming language family
C++ programming language family
Class-based programming languages
Cross-platform software
High-level programming languages
Object-oriented programming languages
Programming languages created in 1983
Programming languages with an ISO standard
Statically typed programming languages