creating variables on the stack

[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 ,

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

detete mypainter;

[ninja9578]

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

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.

[Zlatomir]

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

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:

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)

[Amleto]

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 ,

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

detete mypainter;

QPainter painter(this);

or

QPainter painter;
painter.setParent(this);

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

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

[Amleto]

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

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!

[aamir121a]

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

[Amleto]

I already showed you

[aamir121a]

thank you all, your post have been most helpful