|
Try dimensions.height() or dimensions.width()
Mircea
|
|
|
|
|
Message Closed
modified 15-May-23 19:07pm.
|
|
|
|
|
Member 14968771 wrote: I think I need to read-up on "friend" - that semms to be the real OOP ticket
On the contrary: that might take you into a non-OOP design.
The idea of using public member functions is to make your code independent of internal implementation details of other classes. In your case, a class representing a rectangle might keep a corner of the rectangle and its dimensions. Another one might keep two opposite corners or some other combination. If you try to access private members of the class your code will need to change when or if the implementation of the rectangle changes. If you stick to using only public interface, the internal details of the rectangle class may change but your code will remain the same.
You cannot "buy" your way inside a class using a friend declaration. Just like in real life, the friendship is not a symmetrical relation. If you put a friend QRect declaration inside your class that doesn't give you any special access rights. It gives access rights to QRect to your class but obviously QRect is not going to use those rights. You would need to modify the QRect header file to insert a friend declaration mentioning your class. This is very intrusive and basically defeats the purpose of OOP design.
I cannot make an OOP design course here, but there are some pretty good references available.
Mircea
|
|
|
|
|
Member 14968771 wrote: I guess height and width are QRect public variables derived from "private" data.
No, they are public methods that give you read-only access to private members.
"One man's wage rise is another man's price increase." - Harold Wilson
"Fireproof doesn't mean the fire will never come. It means when the fire comes that you will be able to withstand it." - Michael Simmons
"You can easily judge the character of a man by how he treats those who can do nothing for him." - James D. Miles
|
|
|
|
|
|
One of the steps I invariably do, when debugging, is comment-out private blocks ... essentially rendering all statements public. Now that I get typing ... and that's just for starters.
Without the essential error code (warning?) accompanying a successful compilation/link/running blank form ... there's little more time expendable for me, especially if you're already running debugger and just don't care to get descriptive enough with words and include a code.
So, I'll just cut to the chase.
|
|
|
|
|
Hacking it.
"In testa che avete, Signor di Ceprano?"
-- Rigoletto
|
|
|
|
|
|
But true. 
"In testa che avete, Signor di Ceprano?"
-- Rigoletto
|
|
|
|
|
Message Closed
modified 15-May-23 19:07pm.
|
|
|
|
|
Member 14968771 wrote: In the mean time I'll looking at usage of "friend".
Don't waste your time, since it will not make any difference. You cannot declare your class to be a friend of some other class in the hope of accessing its private variables. If that was possible then the millions of applications would be open to hacking. Do what I suggested above and make use of the information provided in the documentation: that is what it is there for..
|
|
|
|
|
It was serious, actually. If you the designer of the class made a member private then you have two ways to access it: the publicly exposed interface (for instance the get/set methods) or a dirty hack on its bare representation in memory. Typically you cannot use friend because you are not the designer of the class.
"In testa che avete, Signor di Ceprano?"
-- Rigoletto
|
|
|
|
|
Private members are only accessible via public functions.
Try int start_X = QPoint.SetX(dimentions.x2);
|
|
|
|
|
Message Closed
modified 15-May-23 19:07pm.
|
|
|
|
|
This looks suspicious to me:
&MainWindow::Run_DDD_OPTION(testWidget)
It looks like you're trying to create a pointer to whatever Run_DDD_OPTION returns. However, you also say
Run_DDD_OPTION(testWidget); which either means that it returns void or you didn't care what it returned. My guess is the former, which would explain all the error messages. If it returns void, you can't take its address, and there is no lvalue (=a memory address).
EDIT: If you want to pass the function Run_DDD_OPTION as an argument to addAction, just write
addAction(tr("&Device Discovery Dialog(modified Bluetooth scanner)"),
this,
MainWindow::Run_DDD_OPTION
);You may need the & in front of the function name--I haven't done this in a long time, so I have to look it up. --It looks like it's optional. If it doesn't work without it, try it with it.
modified 15-Jun-21 17:48pm.
|
|
|
|
|
Message Closed
modified 15-May-23 19:07pm.
|
|
|
|
|
I don't understand how you want to make addAction's last parameter "more versatile". You'll have to explain that.
|
|
|
|
|
Message Closed
modified 15-May-23 19:07pm.
|
|
|
|
|
I haven't used Qt, so I don't know if I can help. It sounds like a widget is an object, but you're only passing functions and parameters. Would passing an object help?
It's even possible to pass a class's member function[^] as a parameter. I've not used this capability, so you'd have to read up on it if that's what you want.
The problem with passing a function and its parameters is that different functions take different parameters. To deal with that, I think you'd need std::function[^]. Again, that's not something I've used, but now you can look for more details.
My go-to site for C++ is here[^]. It's a bit formal, so sometimes you need to look elsewhere for explanations and examples that are easier to understand. But it will provide you with the right terminology to use when investigating something.
|
|
|
|
|
class A
{
public:
int a;
};
class B:public class A
{
public:
int b;
}
class C: public class B
{
public:
B obj;
}
void main()
{
C obj1(10,20);
}
How do you write constructor for all three class so that the main will get called/?
|
|
|
|
|
Member 15229174 wrote: ...so that the main will get called/?
main() is called by the OS/framework, not you.
If, instead, you wanted to know how to call the base class constructor, how about something like:
class C : public B
{
public:
C(int x, int y) : B(x, y)
{
}
};
"One man's wage rise is another man's price increase." - Harold Wilson
"Fireproof doesn't mean the fire will never come. It means when the fire comes that you will be able to withstand it." - Michael Simmons
"You can easily judge the character of a man by how he treats those who can do nothing for him." - James D. Miles
|
|
|
|
|
Actually an interviewer asked me this question and told that class C contains the object of B class and through main C obj1(10,20) should be passed. Now you have to write constructor in all three class so that in main() function, it will not give an error.
|
|
|
|
|
Since all the member variables are public you only need a constructor in C. And it would still work without that.
|
|
|
|
|
you C class does not have a constructor with 2 parameters.
CI/CD = Continuous Impediment/Continuous Despair
|
|
|
|
|
Actually class C constructor should have had four (Yes, 4, since it contains four variables) parameters. Anyway...
Try
#include <iostream>
using namespace std;
class A
{
public:
int a;
A(int a):a(a){}
};
class B: public A
{
public:
int b;
B(int a, int b): A(a), b(b){}
};
class C: public B
{
public:
B obj;
C(int a, int b): B(a, b), obj(b, a){} friend ostream & operator << (ostream & os, const C & c); };
ostream & operator << (ostream & os, const C & c)
{
os << "a = " << c.a << ", b = " << c.b << ", obj.a = " << c.obj.a << ", obj.b = " << c.obj.b;
return os;
}
int main()
{
C obj1(10,20);
cout << obj1 << endl;
}
"In testa che avete, Signor di Ceprano?"
-- Rigoletto
|
|
|
|
General 
News 
Suggestion 
Question 
Bug 
Answer 
Joke 
Praise 
Rant 
Admin 
Submit an article or tip
