您可以在C ++ 11中像这样

You can do this in C++11 like so

class Menu
{
private:
    std::vector<menuItem> mi = std::vector<menuItem>(20);
};

或者如果您坚持使用C ++ 03，则需要在构造函数的初始值设定项列表中对其进行初始化

or if you are stuck using C++03 you will need to initialize it in the constructors initializer list

class Menu
{
public:
    Menu() : mi(20) {}

private:
    std::vector<menuItem> mi;
};