std::optional<T>::operator bool, std::optional<T>::has_value

Since C++17

Checks whether *this contains a value.

# Declarations

constexpr explicit operator bool() const noexcept;

(since C++17)

constexpr bool has_value() const noexcept;

(since C++17)

# Return value

true if *this contains a value, false if *this does not contain a value.

# Example

#include <optional>
#include <iostream>
 
int main()
{
    std::cout << std::boolalpha;
 
    std::optional<int> opt;
    std::cout << opt.has_value() << '\n';
 
    opt = 43;
    if (opt)
        std::cout << "value set to " << opt.value() << '\n';
    else
        std::cout << "value not set\n";
 
    opt.reset();
    if (opt.has_value())
        std::cout << "value still set to " << opt.value() << '\n';
    else
        std::cout << "value no longer set\n";
}