std::any_cast

 

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std::any

Member functions

any::any

any::~any

any::operator=

Modifers

any::emplace

any::reset

any::swap

Observers

any::has_value

any::type

Non-member functions

swap(std::any)

any_cast

make_any

 

template<class ValueType>     ValueType any_cast(const any& operand);	(1)	(since C++17)
template<class ValueType>     ValueType any_cast(any& operand);	(2)	(since C++17)
template<class ValueType>     ValueType any_cast(any&& operand);	(3)	(since C++17)
template<class ValueType>     const ValueType* any_cast(const any* operand) noexcept;	(4)	(since C++17)
template<class ValueType>     ValueType* any_cast(any* operand) noexcept;	(5)	(since C++17)

Performs type-safe access to the contained object.

Let U be std::remove_cv_t<std::remove_reference_t<ValueType>>.

1) The program is ill-formed if is_constructible_v<ValueType, const U&> is not true.

2) The program is ill-formed if is_constructible_v<ValueType, U&> is not true.

3) The program is ill-formed if is_constructible_v<ValueType, U> is not true.

Parameters

operand

-

target any object

Return value

1-2) Returns static_cast<ValueType>(*std::any_cast<U>(&operand))

3) Returns static_cast<ValueType>(std::move(*std::any_cast<U>(&operand))).

4-5) If operand is not a null pointer, and the typeid of the requested ValueType matches that of the contents of operand, a pointer to the value contained by operand, otherwise a null pointer.

Exceptions

1-3) Throws std::bad_any_cast if the typeid of the requested ValueType does not match that of the contents of operand.

Example

Run this code

#include <string>
#include <iostream>
#include <any>
 
int main()
{
    // simple example 
 
    auto a = std::any(12);
 
    std::cout << std::any_cast<int>(a) << '\n'; 
 
    try {
        std::cout << std::any_cast<std::string>(a) << '\n';
    }
    catch(const std::bad_any_cast& e) {
        std::cout << e.what() << '\n';
    }
 
    // advanced example
 
    a = std::string("hello");
 
    auto& ra = std::any_cast<std::string&>(a); //< reference
    ra[1] = 'o';
 
    std::cout << "a: " << std::any_cast<const std::string&>(a) << '\n'; //< const reference
 
    auto b = std::any_cast<std::string&&>(a); //< rvalue reference (no need for std::move)
 
    // Note, 'b' is a move-constructed std::string, 'a' is now empty
 
    std::cout << "a: " << *std::any_cast<std::string>(&a) //< pointer
        << "b: " << b << '\n';
}

Output:

12
bad any_cast
a: hollo
a: b: hollo