std::any

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Definido no cabeçalho <any>
class any;

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

Predefinição:cpp/utility/any/dsc constructorPredefinição:cpp/utility/any/dsc operator=Predefinição:cpp/utility/any/dsc destructorPredefinição:cpp/utility/any/dsc emplacePredefinição:cpp/utility/any/dsc resetPredefinição:cpp/utility/any/dsc swapPredefinição:cpp/utility/any/dsc has valuePredefinição:cpp/utility/any/dsc type

Modifiers

Observers

Non-member functions

Predefinição:cpp/utility/any/dsc swap2Predefinição:cpp/utility/any/dsc any castPredefinição:cpp/utility/any/dsc make any

Helper classes

Predefinição:cpp/utility/any/dsc bad any cast

Example

#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";
}

Potencial saída:

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

See also

Predefinição:cpp/utility/dsc variant