default init value for struct member of a class

Question

The fragment below is from a VC++ 2008 Express Edition. Say, I have a class with a member that is a struct. I am trying to define default values for the member variables of this class. Why this does not work?

struct Country{
    unsigned chart id;
    unsigned int initials;
    std::string name;
};

class world{
private:
    Country          _country;
    unsigned int  _population;
public:
    world(){};
    world():
             _country(): 
                 id('1'), initials(0), name("Spain") {};
             _population(543000) {}
    :
    :
    ~world(){};
};

Answer 1

There are two ways to initialize the country member data. Like this ...

struct Country{
    unsigned char id;
    unsigned int initials;
    std::string name;
};

class world{
private:
    Country          _country;
public:
     world()
     {
         _country.id = '1';
         _country.initials = 0;
         _country.name = "Spain";
     }
     ~world(){};
};

... or, like this ...

struct Country{
    unsigned char   _id;
    unsigned int    _initials;
    std::string _name;
    Country(
        unsigned char id,
        unsigned int initials,
        const std::string& name
        )
        : _id(id)
        , _initials(initials)
        , _name(name)
    {}
};

class world{
private:
    Country          _country;
public:
    world()
    : _country('1', 0, "Spain")
    {
    }
    ~world(){};
};

Note that in the second example I find it easier to initialize the Country instance because I defined a constructor as a member of the Country struct.

Or, perhaps you want to give the Country type a default constructor:

struct Country{
    unsigned char   _id;
    unsigned int    _initials;
    std::string _name;
    Country()
        : _id('1')
        , _initials(0)
        , _name("Spain")
    {}
};


class world{
private:
    Country          _country;
public:
    world()
    {
    }
    ~world(){};
};

Answer 2

The structure is an aggregate type.

Since it has no constructor you cannot initialise it with normal brackets, you can however use curly braces as you would initialise an array.