object inheritance virtual function run fail error

Question

Shape *shape[100];//global scope
Square sqr;//global scope


void inputdata() {
int len,width;
cout << "enter length";
cin >> len;
cout << "enter width";
cin >> width;

Square sqr(len,width);
shape[0] = &sqr;
//----> if shape[0]->computeArea(); here works fine.
}

void computeArea() {
shape[0]->computeArea(); // --> run fail error
}

Shape is the parent class and square is the sub-class. both have computeArea();

when the code reach computeArea() i am having a weird run fail error. the program just terminate without giving me any errors for me to find and fix it...it just show run fail and stop the program.

the program is able to run properly and show ->computeArea() if the code is within the inputdata() but when i separate it, it just fail to run properly. any solution to this?

From the code you've posted, I don't see a problem, you probably have wrong things elsewhere. — Tony The Lion
– Tony The Lion, Commented May 8, 2013 at 13:32

juanchopanza · Accepted Answer · 2013-05-08 13:32:25Z

3

This Square

Square sqr(len,width);

is an instance which is local to the scope of inputdata. Once you leave that scope, you are left with a dangling pointer in shape[0]. If you want to set the global sqr, you need

sqr = Square(len,width);

You should find a solution that doesn't rely on global variables though.

answered May 8, 2013 at 13:32

juanchopanza

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Comments

Pete Becker · Accepted Answer · 2013-05-08 13:32:16Z

1

Square sqr(len, width) creates an auto object. It goes away when the function returns, even though its address has been stored in shape[0].

answered May 8, 2013 at 13:32

Pete Becker

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Comments

Abdullah Shoaib · Accepted Answer · 2013-05-08 13:37:14Z

0

change your code this way:

Shape *shape[100];//global scope
Square *sqr;//global scope  //make it a pointer or reference


void inputdata() {
int len,width;
cout << "enter length";
cin >> len;
cout << "enter width";
cin >> width;
sqr = new Square(len,width);
shape[0] = sqr;   //remove & here
}
void computeArea() {
shape[0]->computeArea(); 
}

answered May 8, 2013 at 13:37

Abdullah Shoaib

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4 Comments

juanchopanza Over a year ago

There's no need for this dynamic allocation.

Abdullah Shoaib Over a year ago

@juanchopanza What's the problem in dynamic allocation?

juanchopanza Over a year ago

There is no need for it, so why use it? Now you have a resource you need to keep track of and delete.

Abdullah Shoaib Over a year ago

@juanchopanza okay got it. Keeping track of it and deleting it convinces me.

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