C++ ( "see plus plus") is a general-purpose
programming language.
It has imperative, object-oriented and generic
programming features, while also providing
facilities for low-level memory manipulation.
It was designed with a bias toward system
programming and embedded, resource-constrained
and large systems, 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, servers (e.g.
e-commerce, Web search or SQL servers), and
performance-critical applications (e.g. telephone
switches or space probes).
C++ is a compiled language, with implementations
of it available on many platforms.
Many vendors provide C++ compilers, including
the Free Software Foundation, Microsoft, Intel,
and IBM.
C++ is standardized by the International Organization
for Standardization (ISO), with the latest
standard version ratified and published by
ISO in December 2017 as ISO/IEC 14882:2017
(informally known as C++17).
The C++ programming language was initially
standardized in 1998 as ISO/IEC 14882:1998,
which was then amended by the C++03, C++11
and C++14 standards.
The current C++17 standard supersedes these
with new features and an enlarged standard
library.
Before the initial standardization in 1998,
C++ was developed by Bjarne Stroustrup at
Bell Labs since 1979, as an extension of the
C language as he wanted an efficient and flexible
language similar to C, which also provided
high-level features for program organization.
C++20 is the next planned standard thereafter.
Many other programming languages have been
influenced by C++, including C#, D, Java,
and newer versions of C.
== History ==
In 1979, Bjarne Stroustrup, a Danish computer
scientist, began work on "C with Classes",
the predecessor to C++.
The motivation for creating a new language
originated from Stroustrup's experience in
programming for his Ph.D. 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 Ph.D. 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 C++, 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.In 1983, "C with Classes"
was renamed to "C++" (++ being the increment
operator in C), adding new features that included
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,
it included the development of a standalone
compiler for C++, Cfront.
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.
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 templates,
exceptions, namespaces, new casts, and a boolean
type.
After the 2.0 update, 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, and further changes planned for
2020.As of 2017, C++ remains the third most
popular programming language, behind Java
and C.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".
=== 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 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" 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 useful immediately 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 well-defined separate 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 ===
C++ is standardized by an ISO working group
known as JTC1/SC22/WG21.
So far, it has published five revisions of
the C++ standard and is currently working
on the next revision, C++20.
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 (14882:2011) included many additions
to both the core language and the standard
library.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.
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,
ISO/IEC TR 29124:2010 on special mathematical
functions,
ISO/IEC TR 24733:2011 on decimal floating
point arithmetic,
ISO/IEC TS 18822:2015 on the standard filesystem
library,
ISO/IEC TS 19570:2015 on parallel versions
of the standard library algorithms,
ISO/IEC TS 19841:2015 on software transactional
memory,
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++ ConceptsMore
technical specifications are in development
and pending approval, including concurrency
library extensions, a networking standard
library, ranges, and modules.
== 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 [designed]
for 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 that uses the C++
Standard Library stream facility to write
a message to standard output:
=== Object storage ===
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.
==== 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".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.
==== Automatic storage duration objects ====
The most common variable types in C++ are
local variables inside a function or block,
and temporary variables.
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
are created with a call to new and destroyed
explicitly with a call to delete.
=== Templates ===
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.
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 ===
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.
==== Inheritance ====
Inheritance allows one data type to acquire
properties of other data types.
Inheritance from a base class 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 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 is a C++ feature not
found in most other languages, allowing a
class to be derived from more than one base
class; this allows for more elaborate inheritance
relationships.
For example, a "Flying Cat" class can inherit
from both "Cat" and "Flying Mammal".
Some other languages, such as C# or Java,
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 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) and dynamic (resolved at
run-time) polymorphisms, supported by the
language features described above.
Compile-time polymorphism does not allow for
certain run-time decisions, while runtime
polymorphism typically incurs a performance
penalty.
==== Static polymorphism ====
Function overloading 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 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 in C++ provide a sophisticated mechanism
for writing generic, polymorphic code (i.e.
parametric polymorphism).
In particular, through the curiously recurring
template pattern, 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,
they can also be used to let the compiler
resolve recursive conditionals and generate
substantial programs through template metaprogramming.
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
(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.
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.
As a rule of thumb, if any function in the
class is virtual, the destructor should be
as well.
As the type of an object at its creation is
known at compile time, constructors, and by
extension copy constructors, cannot be virtual.
Nonetheless a situation may arise where a
copy of an object needs to be created when
a pointer to a derived object is passed as
a pointer to a base object.
In such a case, a common solution is to create
a clone() (or similar) virtual function that
creates and returns a copy of the derived
class when called.
A member function can also be made "pure virtual"
by appending it with = 0 after the closing
parenthesis and before the semicolon.
A class containing a pure virtual function
is called an abstract class.
Objects cannot be created from an abstract
class; they can only be derived from.
Any derived class inherits the virtual function
as pure and must provide a non-pure definition
of it (and all other pure virtual functions)
before objects of the derived class can be
created.
A program that attempts to create an object
of a class with a pure virtual member function
or inherited pure virtual member function
is ill-formed.
=== Lambda expressions ===
C++ provides support for anonymous functions,
also known as lambda expressions, with the
following form:
The [capture] list supports the definition
of closures.
Such lambda expressions are defined in the
standard as syntactic sugar for an unnamed
function object.
An example lambda function may be defined
as follows:
=== 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.Note that many C++ "styles", like
Google's, forbid usage of exceptions in C++
programs, restricting the language thusly.
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.
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.
== Standard library ==
The C++ standard consists of two parts: the
core language and the standard library.
C++ programmers expect the latter on every
major implementation of C++; it includes aggregate
types (vectors, lists, maps, sets, queues,
stacks, arrays, tuples), algorithms (find,
for_each, binary_search, 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 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
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 (STL).
Useful tools provided by the STL include containers
as the collections of objects (such as vectors
and lists), iterators that provide array-like
access to containers, and algorithms that
perform operations such as searching and sorting.
Furthermore, (multi)maps (associative arrays)
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 features of the library are accessed
by using the #include directive to include
a standard header.
The C++ Standard Library provides 105 standard
headers, of which 27 are deprecated.
The standard incorporates the STL that was
originally designed by Alexander Stepanov,
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.
== Compatibility ==
To give compiler vendors greater freedom,
the C++ standards committee decided not to
dictate the implementation of name mangling,
exception handling, and other implementation-specific
features.
The downside of this decision is that object
code produced by different compilers is expected
to be incompatible.
There were, however, attempts to standardize
compilers for particular machines or operating
systems (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),
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,
were incompatible or redundant in C++, such
as variable-length arrays, 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 (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 (i.e., function overloading).
== Criticism ==
Despite its widespread adoption, some notable
programmers have criticized the C++ language,
including Linus Torvalds, Richard Stallman,
Joshua Bloch, Ken Thompson, and Donald Knuth.
One of the most often criticised points of
C++ is its perceived complexity as a language,
with the criticism that a large number of
non-orthogonal features in practice necessitates
restricting code to subset of C++, thus eschewing
the readability benefits of common style and
idioms.
As expressed by Joshua Bloch: 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 (1993, commenting on pre-standardized
C++), who said of Edsger Dijkstra 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, 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, 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: "within
C++, there is a much smaller and cleaner language
struggling to get out".Other complaints may
include a lack of reflection or garbage collection,
slow compilation times, perceived feature
creep, and verbose error messages, particularly
from template metaprogramming.
== See also ==
Comparison of programming languages
List of C++ compilers
Outline of C++
C++ Libraries (category)
== References ==
== 
Further reading ==
== 
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 is a director of the organization
