CODEWITHSUNDEEP
c++
f c
f c

Reputation:

default init value for struct member of a class

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(){};
};

Upvotes: 0

Views: 1753

Answers (2)

ChrisW
ChrisW

Reputation: 56113

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(){};
};

Upvotes: 6

Jezzletek
Jezzletek

Reputation: 113

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.

Upvotes: 2

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