C + + class constructors, copy constructors, assignment functions, destructors, some attention to __jquery

An empty class, the compiler defaults to generating constructors, copying constructors, assigning functions, destructors, and a class. If you override the copy constructor, you must customize a constructor. The following code compiles an error: Error C2512: "B": no suitable default constructor available

Class B
{public
:
    B (const b &b)
    {
    }
};

int main (void)
{
    b b;

    GetChar ();
    return 0;
}

Amended to:

Class B
{public
:
    B () {}
    B (const b &b)
    {
    }
};

int main (void)
{
    b b;

    GetChar ();
    return 0;
}

Correct spelling of copy constructors and assignment functions (if (this!= &b))

Class B
{public
:
    B (int v)
    {
        m_value = v;
    }

    B (const b &b)
    {
        m_value = b.m_value;
    }

    b &operator = (const b &b)
    {
        if (this!= &b)
        {
            m_value = b.m_value;
        }
        return *this;
    }

Private:
    int m_value;

};

When a function returns a value as an object, consider the efficiency of the return statement.

b createObj0 (void)
{return
    B (0);
}
b createObj1 (void)
{b
    b (0);
    return b;
}

CreateObj0 creates a temporary object and returns it, the compiler creates and initializes the temporary object directly in the external storage unit, eliminating the process of copying and destructor. CreateObj1 creates a B object, and then copies the construct to copy B to the external storage unit, and then the B object is also destructor. Compare the following two groups of code with the results of your operation:

#include <stdio.h>

int g_counter = 0;
Class B
{public
:
    b (void)
    {
        m_value = g_counter++;
        printf ("B () m_value=%d\n", m_value);
    }

    ~b ()
    {
        printf ("~b () m_value=%d\n", m_value);
    }

    B (const b &a)
    {
        m_value = g_counter++;
        printf ("B (const b &a) m_value=%d\n", m_value);
    }

    b &operator= (const b&a)
    {
        printf ("B &operator= (const b&a) \ n");
        return *this;
    }

Private:
    int m_value;

};

b createObj0 (const b b)
{
    b bb (b);
    return BB;
}

b createObj1 (const B)
{return
    B (b);
}

int main (void)
{
    B __b;
    B _b = createObj0 (__b);
	return 0;
}

Run Result:

#include <stdio.h>

int g_counter = 0;
Class B
{public
:
    b (void)
    {
        m_value = g_counter++;
        printf ("B () m_value=%d\n", m_value);
    }

    ~b ()
    {
        printf ("~b () m_value=%d\n", m_value);
    }

    B (const b &a)
    {
        m_value = g_counter++;
        printf ("B (const b &a) m_value=%d\n", m_value);
    }

    b &operator= (const b&a)
    {
        printf ("B &operator= (const b&a) \ n");
        return *this;
    }

Private:
    int m_value;

};

b createObj0 (const b b)
{
    b bb (b);
    return BB;
}

b createObj1 (const B)
{return
    B (b);
}

int main (void)
{
    B __b;
    B _b = createObj1 (__b);
	return 0;
}

Run Result: