如何正确地将值赋给具有类数据类型的结构的成员？

Question

Please kindly see below for the codes. Its compiling successfully but the expected result is not working. Im very confused because my initialization of the array is valid,

//cbar.h
class CBar
{
public:
    class CFoo
    {
    public:
       CFoo( int v ) : m_val = v {}
       int GetVal() { return m_val; }
    private:
       int m_val;
    };
public:
    static const CFoo foo1;
    static const CFoo foo2;

public:
    CBar( CFoo foo ) m_barval( foo.GetVal() ){}
    int GetFooVal() { return m_barval; }
private:
    int m_barval;
};

//cbar.cpp
const CBar::CFoo foo1 = CBar::CFoo(2);
const CBar::CFoo foo2 = CBar::CFoo(3);

//main.cpp
struct St
{
    CBar::CFoo foo;
};

St st[] = { CBar::foo1, CBar::foo2 };

for( int i=0; i<sizeof(st)/sizeof(St); i++ )
{
    CBar cbar( st[i].foo );
    std::cout << cbar.GetFooVal() << std::endl;
}

But then when I change the St::foo to a pointer. And like assign the address of CBar::foo1 or CBar::foo2, its working, like this,

//main.cpp
struct St
{
    const CBar::CFoo *foo;
};

St st[] = { &CBar::foo1, &CBar::foo2 };

for( int i=0; i<sizeof(st)/sizeof(St); i++ )
{
    CBar cbar( *st[i].foo );
    std::cout << cbar.GetFooVal() << std::endl;
}

The real problem is. The app should output

2
3

Please advice.

Many thanks.

Answer 1

The problem is coming from these two lines:

const CBar::CFoo foo1 = CBar::CFoo(2);
const CBar::CFoo foo2 = CBar::CFoo(3);

which is not doing as you intended them to be doing. That is, these statements do not initialize foo1 and foo2 static members from the class CBar , rather they define global variables with name foo1 and foo2!

All you need to write:

const CBar::CFoo CBar::foo1 = CBar::CFoo(2);
const CBar::CFoo CBar::foo2 = CBar::CFoo(3);

Have you noticed the difference? Yes, you need to qualify "foo1" and "foo2" with CBar .

However, I would prefer to write:

const CBar::CFoo CBar::foo1(2);
const CBar::CFoo CBar::foo2(3);

which is exactly same!

---

Another problem is this line:

CFoo( int v ) : m_val = v {}

which is wrong. You cannot use "=" in the initialization-list. Write this:

CFoo( int v ) : m_val(v) {}

Now your code should work! :-)