std::any_cast - cppreference.com (original) (raw)

Performs type-safe access to the contained object.

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

4,5) The program is ill-formed if std::is_void_v<T> is true.

[edit] Parameters

[edit] Return value

1,2) Returns static_cast<T>(*std::any_cast<U>(&operand)).

1. Returns static_cast<T>(std::move(*std::any_cast<U>(&operand))).

4,5) If operand is not a null pointer, and the

typeid

of the requested T matches that of the contents of operand, a pointer to the value contained by operand, otherwise a null pointer.

[edit] Exceptions

[edit] Example

#include #include #include #include #include   int main() { // Simple example auto a1 = std::any(12); std::cout << "1) a1 is int: " << std::any_cast(a1) << '\n';   try { auto s = std::any_cast<std::string>(a1); // throws } catch (const std::bad_any_cast& e) { std::cout << "2) " << e.what() << '\n'; }   // Pointer example if (int* i = std::any_cast(&a1)) std::cout << "3) a1 is int: " << *i << '\n'; else if (std::string* s = std::any_cast<std::string>(&a1)) std::cout << "3) a1 is std:🧵 " << *s << '\n'; else std::cout << "3) a1 is another type or unset\n";   // Advanced example a1 = std::string("hello"); auto& ra = std::any_cast<std::string&>(a1); // reference ra[1] = 'o';   std::cout << "4) a1 is string: " << std::any_cast<const std::string&>(a1) << '\n'; // const reference   auto s1 = std::any_cast<std::string&&>(std::move(a1)); // rvalue reference // Note: “s1” is a move-constructed std:🧵 static_assert(std::is_same_v<decltype(s1), std::string>);   // Note: the std::string in “a1” is left in valid but unspecified state std::cout << "5) a1.size(): " << std::any_cast<std::string>(&a1)->size() // pointer << '\n' << "6) s1: " << s1 << '\n'; }

Possible output:

1. a1 is int: 12
2. bad any_cast
3. a1 is int: 12
4. a1 is string: hollo
5. a1.size(): 0
6. s1: hollo

[edit] Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.