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

constexpr explicit operator bool() const noexcept;

constexpr bool has_value() const noexcept;

Vérifie si *this contient une valeur.

Paramètres

(aucun)

Valeur de retour

true si * this contient une valeur, false si * this ne contient pas de valeur.

Exemple

#include <iostream>
#include <optional>
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";
}

false
value set to 43
value no longer set