std::any

 

C++

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Technical Specifications

 

Utilities library

Type support (basic types, RTTI, type traits)
Dynamic memory management
Error handling
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initializer_list (C++11)
bitset
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common_comparison_category
Common vocabulary types
pair tuple (C++11) apply (C++17) make_from_tuple (C++17)	optional (C++17) any (C++17) variant (C++17)
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swap
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chars_format (C++17)
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declval (C++11)
as_const (C++17)
launder (C++17)

 

std::any

Member functions

any::any

any::~any

any::operator=

Modifiers

any::emplace

any::reset

any::swap

Observers

any::has_value

any::type

Non-member functions

swap(std::any)

any_cast

make_any

 

Defined in header <any>
class any;		(since C++17)

The class any describes a type-safe container for single values of any type.

1) An object of class any stores an instance of any type that satisfies the constructor requirements or is empty, and this is referred to as the state of the class any object. The stored instance is called the contained object. Two states are equivalent if they are either both empty or if both are not empty and if the contained objects are equivalent.

2) The non-member any_cast functions provide type-safe access to the contained object.

Implementations are encouraged to avoid dynamic allocations for small objects, but such an optimization may only be applied to types for which std::is_nothrow_move_constructible returns true.

Member functions

(constructor)	constructs an any object (public member function)
operator=	assigns an any object (public member function)
(destructor)	destroys an any object (public member function)
Modifiers
emplace	change the contained object, constructing the new object directly (public member function)
reset	destroys contained object (public member function)
swap	swaps two any objects (public member function)
Observers
has_value	checks if object holds a value (public member function)
type	returns the typeid of the contained value (public member function)

Non-member functions

std::swap(std::any) (C++17)	specializes the std::swap algorithm (function)
any_cast (C++17)	type-safe access to the contained object (function template)
make_any (C++17)	creates an any object (function template)

Helper classes

bad_any_cast (C++17)

exception thrown by the value-returning forms of any_cast on a type mismatch (class)

Example

Run this code

#include <any>
#include <iostream>
 
int main()
{
    std::cout << std::boolalpha;
 
    // any type
    std::any a = 1;
    std::cout << a.type().name() << ": " << std::any_cast<int>(a) << '\n';
    a = 3.14;
    std::cout << a.type().name() << ": " << std::any_cast<double>(a) << '\n';
    a = true;
    std::cout << a.type().name() << ": " << std::any_cast<bool>(a) << '\n';
 
    // bad cast
    try
    {
        a = 1;
        std::cout << std::any_cast<float>(a) << '\n';
    }
    catch (const std::bad_any_cast& e)
    {
        std::cout << e.what() << '\n';
    }
 
    // has value
    a = 1;
    if (a.has_value())
    {
        std::cout << a.type().name() << '\n';
    }
 
    // reset
    a.reset();
    if (!a.has_value())
    {
        std::cout << "no value\n";
    }
 
    // pointer to contained data
    a = 1;
    int* i = std::any_cast<int>(&a);
    std::cout << *i << "\n";
}

Possible output:

i: 1
d: 3.14
b: true
bad any_cast
i
no value
1