How to set class member as constant?

Question

In the code below, I have declared string name in class SHAPE so that the sub-classes can have a constant name.

But, the g++ compiler gives the error inside CIRCLE class that 'name' does not name a type.

class SHAPE
{
    protected:
    string name;
};

class CIRCLE : public SHAPE
{
    name = "circle";
    public:
    void display()
    {
        cout<<name;
    }
};

I am new to OOP and C++. Any help in correcting and improving my code will be appreciated.

Read about [member initialization lists](http://en.cppreference.com/w/cpp/language/initializer_list). — Some programmer dude, Aug 04 '14 at 11:08

Johan Hjalmarsson · Answer 1 · 2014-08-04T11:23:06.913

1

You need constructors for non-static classes if you want to be able to run them.

I'd suggest something like this:

class SHAPE
{
    protected:
    SHAPE(const string& name_) : name(name_) {}  //Sets the string name.
    const string name;
};

class CIRCLE : public SHAPE
{
    public:
    CIRCLE() : SHAPE("TheNameYouWant") {}  //Call parents constructor
    void display()
    {
        cout<<name;
    }
};

So now you call it like this:

CIRCLE c1("someName");
c1.display();

It will still be impossible to create a SHAPE object, meaning that this won't work (if that is what you want):

SHAPE s1("someName");

edited Aug 04 '14 at 11:23

answered Aug 04 '14 at 11:06

Johan Hjalmarsson

3,433
4
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You should pass strings by const reference. – Neil Kirk Aug 04 '14 at 11:10
@mtijn Yeah, I did. Also used "new" wrong ^^ too much C# and too little c++ lately. Dont know if the code will run since I cant testrun it atm. – Johan Hjalmarsson Aug 04 '14 at 11:11
You can use ideone.com – Neil Kirk Aug 04 '14 at 11:12
What is a "non-static class"? What is a "static class"? – Lightness Races in Orbit Aug 04 '14 at 11:14
@LightnessRacesinOrbit static classes are classes that you don't have to create an object of before running. So they don't have a constructor and only have static variables and methods. – Johan Hjalmarsson Aug 04 '14 at 11:15
I want object of class `CIRCLE` to have `name = circle` automatically, instead of passing name as parameter – Barun Aug 04 '14 at 11:20
@Barun Then just hardcore it like this: `CIRCLE() : SHAPE("theNameYouWant") {}`. I edited the code example to show what I mean – Johan Hjalmarsson Aug 04 '14 at 11:21

Massimo Costa · Accepted Answer · 2014-08-04T12:22:39.313

1

you have to create a class contructor

class CIRCLE : public SHAPE
{

public:
    CIRCLE() {
        name="circle";
    }
    void display()
    {
        cout<<name;
    }
};

edited Aug 04 '14 at 12:22

answered Aug 04 '14 at 11:07

Massimo Costa

1,864
15
23

Syntactically valid code might help. – Lightness Races in Orbit Aug 04 '14 at 11:11
That does the work. Could you add some comment in the code for more information. – Barun Aug 04 '14 at 11:22

score 0 · Answer 3 · answered Aug 04 '14 at 11:07

0

class SHAPE
{
public:
    explicit SHAPE(const string& name)
    : name(name)
    {
    }

    const string& GetName() const
    {
        return name;
    }

protected:
    string name;
};

class CIRCLE : public SHAPE
{
public:
    explicit CIRCLE(const string& name)
    : SHAPE(name)
    {
    }
};

int main()
{
    CIRCLE c("circle1");
    cout << c.GetName() << "\n";
}

answered Aug 04 '14 at 11:07

Neil Kirk

21,327
9
53
91

1

I don't see how a code dump without explanation is helpful for this guy. Poor way to teach. – Lightness Races in Orbit Aug 04 '14 at 11:11
@LightnessRacesinOrbit That's why internet tutorials were invented. He can compile it, step through the code, look up what he doesn't understand. At least I give some good practices for him to see. – Neil Kirk Aug 04 '14 at 11:12
Internet tutorials can kiss me. He should be learning from a good book. http://stackoverflow.com/questions/388242/the-definitive-c-book-guide-and-list – Lightness Races in Orbit Aug 04 '14 at 11:14
Honestly, I didn't get anything from this. – Barun Aug 04 '14 at 11:32
1

@Barun Then learn until you do. Only you can make yourself a good programmer! – Neil Kirk Aug 04 '14 at 12:39

How to set class member as constant?

3 Answers3