Suppose I have derived class of:

Can anyone tell me whether the line 4 syntax is correct, and if it does, what does it means? Thanks.



yengzhai

__________________
yengzhai

The syntax is correct.

When you create an object of myDerivedClass type, the constructor used will be the myBaseClass() constructor. In other words the constructor for myDerivedClass uses the constructor inherited from myBaseClass.

Alan


Alan

Thanks. Because I have never seen such syntax, normally what I get from book is:

myDerivedClass :: myDerivedClass(int a, int b) : myBaseClass(x, y)
{
public:
...
}

So the above statement is equivalent to the statement that I posted the other day?

If the statement is correct, but somehow I still get the meaningless output from the screen. Below is my coding:


If the above coding is executed, the output will have these kinda numbers:

-858993460 -858993460
where the expected output should be 5 and 6.

Is there any mistakes in my sample program?






yengzhai

The first (but not last) of the errors is here

                    it is like this:
.................................................. ...........
myDerivedClass(int a, int b) : myBaseClass(x, y) {} // line 4
.................................................. ............

                    it should be:
.................................................. ............
myDerivedClass(int a, int b) : myBaseClass(a,b) {} // line 4
.................................................. ...........

Good luck with the rest of the errors!

Hello
   Your program should change to this style

#include <iostream.h>

class myBaseClass
{
public:
    myBaseClass(int , int);
    void print();

private:
    int x;
    int y;
};

// derived class
class myDerivedClass:public myBaseClass
{
public:
    myDerivedClass(int x, int y):myBaseClass(x, y){ //IZRAILEVICH1 revised here
    a=x;
    b=y;
    }
    void print();

private:
    int a;
    int b;
};

// base class implementation
myBaseClass :: myBaseClass(int param1, int param2)
{
    x = param1;
    y = param2;
}
void myDerivedClass :: print() // Added by me
{
    cout<<a<<" "<<b<<endl;
}

void myBaseClass :: print()
{
    cout<<x<<" "<<y<<endl;
}

// in main program


int main(int argc, char* argv[])
{
    printf("Hello World!\n");

    myDerivedClass derivedClass(5, 6);
    derivedClass.print();

    return 0;
}

// the output is :
    Hello World!
    5 6

zhangyanbo

I THINK ITS RIGHT.

may be you should define the print function as virtual