Classes

 

C++

Language

Standard library headers

Concepts

Utilities library

Strings library

Containers library

Algorithms library

Iterators library

Numerics library

Input/output library

Localizations library

Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

 

C++ language

General topics
Preprocessor Comments Keywords	ASCII chart Escape sequences History of C++
Flow control
Conditional execution statements
if statement	switch statement
Iteration statements
for loop range-for loop (C++11)	while loop do-while loop
Jump statements
continue statement break statement	goto statement return statement
Functions
function declaration
lambda function declaration
function template
inline specifier
exception specifications (deprecated)
noexcept specifier (C++11)
Exceptions
throw expression	try-catch block
Namespaces
namespace declaration	namespace aliases
Types
fundamental types compound types enumeration types	union types function types
decltype specifier (C++11)
Specifiers
cv specifiers
storage duration specifiers
constexpr specifier (C++11)
auto specifier (C++11)
alignas specifier (C++11)
Initialization
default initialization value initialization zero initialization copy initialization direct initialization	aggregate initialization list initialization (C++11) constant initialization reference initialization

Literals
integer literals character literals floating-point literals string literals	boolean literals nullptr (C++11) user-defined (C++11)
Expressions
value categories order of evaluation	operators operator precedence
alternative representations
Utilities
Types
typedef declaration
type alias declaration (C++11)
attributes (C++11)
Casts
implicit conversions
const_cast conversion
static_cast conversion
dynamic_cast conversion
reinterpret_cast conversion
C-style and functional cast
Memory allocation
new expression	delete expression
Classes
class declaration this pointer access specifiers	friend specifier initializer lists
Class-specific function properties
virtual function override specifier (C++11) final specifier (C++11)	explicit (C++11) static
Special member functions
default constructor copy constructor move constructor (C++11)	copy assignment move assignment (C++11) destructor
Templates
class template
function template
template specialization
parameter packs (C++11)
Miscellaneous
Inline assembly

 

A class is a user-defined type.

A class type is defined by class-specifier, which appears in decl-specifier-seq of the declaration syntax. The class specifier has the following syntax:

class-key attr class-head-name base-clause { member-specification }	(1)

class-key	-	one of class, struct, union
attr(C++11)	-	optional sequence of any number of attributes
class-head-name	-	the name of the class that's being defined. Optionally prepended by nested-name-specifier (sequence of names and scope-resolution operators, ending with scope-resolution operator), optionally followed by keyword final. The name may be omitted, in which case the class is unnamed (note that unnamed class cannot be final)
base-clause	-	optional list of one or more parent classes and the model of inheritance used for each (see derived class)
member-specification	-	list of access specifiers, member object and member function declarations and definitions (see class definition)

The class keys struct and class are indistinguishable in C++, except that the default access mode and default inheritance mode are public if class declaration uses the struct class-key and private if the class declaration uses the class class-key. Both class and struct can be used in a class definition.

The use of the class key union results in a union definition, which defines a class that holds only one of its data members at a time.

A class can have four kinds of members

1) data members

a) non-static data members, including bit fields.

b) static data members

2) member functions

a) non-static member functions

b) static member functions

3) nested types

a) nested classes and enumerations defined within the class definition

b) aliases of existing types, defined with typedef or type alias declarations

4) enumerators from all unscoped enumerations defined within the class

All members are defined at once in the class definition, they cannot be added later.

A class with at least one declared or inherited virtual member function is polymorphic. Objects of this type have runtime type information stored as part of the object, which may be queried with dynamic_cast and typeid, and the virtual member functions participate in dynamic binding.

A class with at least one declared or inherited pure virtual member function is abstract. Objects of this type cannot be created.

A class with a constexpr constructor is a literal type: objects of this type can be manipulated by constexpr functions at compile time.

Some member functions are special: under certain circumstances they are defined by the compiler even if not defined by the user. They are:

• Default constructor
• Copy constructor
• Move constructor (since C++11)
• Copy assignment operator
• Move assignment operator (since C++11)
• Destructor