Extending the namespace std

 

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	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

 

Adding declarations to std

It is undefined behavior to add declarations or definitions to namespace std or to any namespace nested within std, with a few exceptions noted below

#include <utility>
namespace std {
    // a function definition added to namespace std: undefined behavior
    pair<int, int> operator+(pair<int, int> a, pair<int, int> b) {
        return {a.first+b.first, a.second+b.second};
    }
}

It is allowed to add template specializations for any standard library template to the namespace std only if the declaration depends on a user-defined type and the specialization satisfies all requirements for the original template, except where such specializations are prohibited.

• It is undefined behavior to declare a full specialization of any member function of a standard library class template

• It is undefined behavior to declare a full specialization of any member function template of a standard library class or class template

• It is undefined behavior to declare an full or partial specialization of any member class template of a standard library class or class template.

• None of the type traits defined in <type_traits> may be specialized for a user-defined type, except for std::common_type.

• Specializing the template std::complex for any type other than float, double, and long double is unspecified.

• Specializations of std::hash for user-defined types must satisfy Hash requirements.

• Specializations of std::atomic must have a deleted copy constructor, a deleted copy assignment operator, and a constexpr value constructor.

• Specializations of std::shared_ptr and std::weak_ptr must be CopyConstructible and CopyAssignable. In addition, specializations of std::shared_ptr must be LessThanComparable, and convertible to bool.

• Specializations of std::istreambuf_iterator must have a trivial copy constructor, a constexpr default constructor, and a trivial destructor.

• Specializations of std::numeric_limits must define all members declared static constexpr in the primary template, in such a way that they are usable as integral constant expressions.

• std::unary_function and std::binary_function may not be specialized.

It is allowed to explicitly instantiate a template defined in the standard library only if the declaration depends on the name of a user-defined type and the instantiation meets the standard library requirements for the original template.

Other restrictions

The namespace std may not be declared as an inline namespace.