Pure virtual function error

[newGuy23423]

I have a base class with a pure virtual function, and a derived class that implements it. When I try to call this function from the sub class object, I get a message:

Request for member 'stdOutAttrib' in rect, which is of non class type Rectangle()

Now Rectangle is indeed a class, so I don't know why it thinks it isn't. Also not sure why it has it as Rectangle() with the parentheses. Virtual functions are new to me, so bare with me.

[guestgulkan]

Lets see your code..
( if you are on Windows - you might be inadvertantly calling the Windows API Rectangle() function )

[Athar]

You probably wrote Rectangle rect();, which is a function declaration.
It should be Rectangle rect;

[newGuy23423]

Why can't I use Rectangle rect(); ? Isn't that calling the default constructor?

[JLBorges]

std::string foo ; // foo is a default constructed std::string

std::string bar() ; // declare bar
// bar is a function taking no parameters and returning a std::string 

[newGuy23423]

I thought you did it first way (without parentheses) if there is no user- defined default constructor, and the second way if there is a user-defined default constructor?

I don't really see the difference here

[JLBorges]

> I thought you did it first way (without parentheses) if there is no user- defined default constructor,
> and the second way if there is a user-defined default constructor?

No.


> I don't really see the difference here

Try compiling this:

struct A { A() { /* default constructor */ } A(int) { /* constructor with arg */ } } ;

int main()
{
    A one ; // one: default-constructed A (definition)
    A* pa = &one ; // fine.

    A two(23) ; // two: object of type A initialized with 23 (definition)
    pa = &two ; // also fine

    A three() ; // three: function returning an A and taking no args (declaration)
    pa = &three ; // *** error: can't convert from pointer to function to pointer to A
}

[Cubbi]

This is one of those issues where Stroustrup tells everyone to forgo the old ways and use curlies in all situations:

A one{}; // default ctor
A two{23}; // single-argument ctor 

I wonder if that will catch on.

[Catfish3]

http://yosefk.com/c++fqa/ctors.html#fqa-10.2

[newGuy23423]

Ah now I get it! Catfish, that article was an interesting read. Though it definitely seemed to have the vibe of "Don't touch C++, it's awful" :/

[JLBorges]

> I wonder if that will catch on.

If uniform initialization does catch on, the overwhelming beneficiaries would be students who are starting out to learn C++; it makes C++ programming simpler and more intuitive.

Though I doubt that it will catch on. The fundamental problem with C++ is its teachers - in schools, on the web, everywhere. Fourteen years after std::vector<> and std::string, students of C++ are still not learning programming. Instead, right from day two, they are being overwhelmed by the intricacies C-style arrays and dynamic memory management.

[Cubbi]

newGuy23423 wrote:

Though it definitely seemed to have the vibe of "Don't touch C++, it's awful" :/

That's the stated goal of that site. Don't take it seriously.