creating variables on the stack

Can some please show me , how to create class instances on the stack , the ones I am interested in are the ones which need to have arguments passed on the constructor ,
I use QT as C++ dev environment ,

Code:

---


QString mystring;  // that is good  , as you can see the class instance do not require a argument to be // passed on to the constructor
// how to do this in the header file

QPainter mypainter(this);

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when ever their is a argument to be passed passed on the constructor I end up doing this;

QPainter *mypainter; // in the header

and then in CPP file

mypianter = new QPainter(this);

I was wondering if there was a way to this on the stack as oppose to the heap.
saves me the trouble of deteting the class instance later

as in

Code:

---

detete mypainter;

---

I'm not 100% sure, but I think this is acceptable:

Code:

---

QPainter painter;

...

new(&painter) QPainter(this);

---

But if QPainter is inheritable, I would create a sub-class where you can just call a seperate method to reinitialize.

You can create object on the stack and pass parameters to them, there is no problem there:

Code:

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QString stringName("Whatever string you like");

---

The only "problem" is when you want the default constructor (without arguments) then you can't have () for default constructor:

Code:

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QString str0; //ok create an empty QString
QString str1(); //compiler thinks that you want a function:
//named str1 that doesn't take parameters and returns a QString

---

LE: With Qt you need to be careful about the objects that you don't need to delete (the parent-child relationship)

Quote:

---

Originally Posted by aamir121a

Can some please show me , how to create class instances on the stack , the ones I am interested in are the ones which need to have arguments passed on the constructor ,
I use QT as C++ dev environment ,

Code:

---


QString mystring;  // that is good  , as you can see the class instance do not require a argument to be // passed on to the constructor
// how to do this in the header file

QPainter mypainter(this);

---

when ever their is a argument to be passed passed on the constructor I end up doing this;

QPainter *mypainter; // in the header

and then in CPP file

mypianter = new QPainter(this);

I was wondering if there was a way to this on the stack as oppose to the heap.
saves me the trouble of deteting the class instance later

as in

Code:

---

detete mypainter;

---

---

Code:

---

QPainter painter(this);

---

or

Code:

---

QPainter painter;
painter.setParent(this);

---

Code:

---

class someclass
{
public:
  someclass(QWidget* parent = 0);
  QPainter m_painter;
};

someclass::someclass(QWidget* parent )
: m_painter(parent)
{
}

---

Quote:

---

Originally Posted by ninja9578

I'm not 100% sure, but I think this is acceptable:

Code:

---

QPainter painter;

...

new(&painter) QPainter(this);

---

But if QPainter is inheritable, I would create a sub-class where you can just call a seperate method to reinitialize.

---

That doesnt look good - it overwrites an object that already exists!

QPainter was just an example how about objects which cannot be instanced without passing some arguments to the constractor

I already showed you

thank you all, your post have been most helpful