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Qt-interest Archive, May 2007
How to make a function return a double array of qpoint ?

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Message 1 in thread

Hi..

How can i make a function return a double array of qpoint ?

like this:

QPoint pl [ 100 ] [ 200 ] ;
pl = theFunction();


Thanks :-)

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Message 2 in thread

QPoint ** foo( int & rowCnt, int & colCnt )

Or pass it as a reference

Void foo( QPoint & pl[ 100 ][ 200 ] )

Or

Use QList< QList< QPoint > > which IMHO is preferred, since memory
bounds can be checked easier with assertions

Scott





> -----Original Message-----
> From: hihihi [mailto:hihihi@xxxxxxxxxx]
> Sent: Tuesday, May 22, 2007 12:04 AM
> To: qt-interest@xxxxxxxxxxxxx
> Subject: How to make a function return a double array of qpoint ?
> 
> Hi..
> 
> How can i make a function return a double array of qpoint ?
> 
> like this:
> 
> QPoint pl [ 100 ] [ 200 ] ;
> pl = theFunction();
> 
> 
> Thanks :-)
> 
> --
> To unsubscribe - send a mail to qt-interest-request@xxxxxxxxxxxxx with
> "unsubscribe" in the subject or the body.
> List archive and information: http://lists.trolltech.com/qt-interest/

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Message 3 in thread

Or use QVector, or one of the other container classes:
http://doc.trolltech.com/4.2/containers.html

you can easily return those containers by value.

Cheers,
Peter

> -----Original Message-----
> From: Scott Aron Bloom [mailto:scott@xxxxxxxxxxxx]
> Sent: Tuesday, May 22, 2007 9:20 AM
> To: hihihi; qt-interest@xxxxxxxxxxxxx
> Subject: RE: How to make a function return a double array of qpoint ?
> 
> QPoint ** foo( int & rowCnt, int & colCnt )
> 
> Or pass it as a reference
> 
> Void foo( QPoint & pl[ 100 ][ 200 ] )
> 
> Or
> 
> Use QList< QList< QPoint > > which IMHO is preferred, since memory
> bounds can be checked easier with assertions
> 
> Scott
> 
> 
> 
> 
> 
> > -----Original Message-----
> > From: hihihi [mailto:hihihi@xxxxxxxxxx]
> > Sent: Tuesday, May 22, 2007 12:04 AM
> > To: qt-interest@xxxxxxxxxxxxx
> > Subject: How to make a function return a double array of qpoint ?
> >
> > Hi..
> >
> > How can i make a function return a double array of qpoint ?
> >
> > like this:
> >
> > QPoint pl [ 100 ] [ 200 ] ;
> > pl = theFunction();
> >
> >
> > Thanks :-)

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Message 4 in thread

On Tuesday 22 May 2007 09:20, Scott Aron Bloom wrote:


Over the years I have tried many times to understand the pointer stuff.
Part i understand and can use it.
With the stuff below my mind goes blankertyblank 
< Information in compatible with current brain. > 
< Brain not at home. >

If someone can answer the questions below for me, then i will print the answer 
on paper and stick it to the wall, for future reference. :-)

> QPoint ** foo( int & rowCnt, int & colCnt )

const int size1=2000;
const int size2=50;

class Cm {
  public:
    QPoint **experiment4();
}

QPoint ** Cm::experiment4()
{
  QPoint pointsArray[ size1][size2];
  return pointsArray;
}

compile error: cannot convert âQPoint (*)[50]â to âQPoint**â in return

How can this be made to work ?


> Or pass it as a reference
>
> Void foo( QPoint & pl[ 100 ][ 200 ] )

const int size1=2000;
const int size2=50;

class Cm {
  public:
    void experiment3( QPoint[ size1 ][ size2 ] );
}

void Cm::experiment3( QPoint &pl[ size1 ][ size2 ] )
{

}

compiler error: declaration of âplâ as array of references
compiler error: prototype for âvoid Cm::experiment3()â does not match any in 
class âCmâ
compiler error: candidate is: void Cm::experiment3(QPoint (*)[50])

How can this be made to work ?

Thank you very much.

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Message 5 in thread

> Over the years I have tried many times to understand the pointer
stuff.
> Part i understand and can use it.
> With the stuff below my mind goes blankertyblank
[broken code that has many mistakes deleted]

Which is another reason to leave the (dangerous and complicated) pointer
stuff alone. Use QVector or QList instead, and all will be fine :)

const int size1=2000;
const int size2=50;

class Cm {
  public:
    QVector<QVector<QPoint> > experiment();
}; 

QVector<QVector<QPoint> > Cm::experiment()
{
	QVector<QVector<QPoint> > pointsArray;
	pointsArray.fill(QVector<QPoint>(size2),size1); 
	return pointsArray;
}

Cm test_cm;
QVector<QVector<QPoint> > table = 	test_cm.experiment();
QPoint p = table[1][2]; // ok

// gives an error (instead of silently accessing some random memory)
QPoint p2 = table[5000][9000]; 

Cheers,
Peter

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Message 6 in thread

On Tuesday 22 May 2007 12:29, Peter Prade wrote:
> > Over the years I have tried many times to understand the pointer
>
> stuff.
>
> > Part i understand and can use it.
> > With the stuff below my mind goes blankertyblank
>
> [broken code that has many mistakes deleted]
>
> Which is another reason to leave the (dangerous and complicated) pointer
> stuff alone. Use QVector or QList instead, and all will be fine :)
>
> const int size1=2000;
> const int size2=50;
>
> class Cm {
>   public:
>     QVector<QVector<QPoint> > experiment();
> };
>
> QVector<QVector<QPoint> > Cm::experiment()
> {
> 	QVector<QVector<QPoint> > pointsArray;
> 	pointsArray.fill(QVector<QPoint>(size2),size1);

On this line i get:
 error: no matching function for call to âQPtrVector<QPtrVector<QPoint> 
>::fill(QPtrVector<QPoint>, const int&)â
/usr/lib/qt-3.3/include/qptrvector.h:71: note: candidates are: bool 
QPtrVector<type>::fill(const type*, int) [with type = QPtrVector<QPoint>]
gmake[1]: *** [micrometer.o] Error 1


> 	return pointsArray;
> }


How do i assign one qpoint to the qvectors ?

QVector<QVector<QPoint> > Cm::experiment()
{
  
   QVector<QVector<QPoint> > pointsArray;
   for(int count1=0; count1<size1 ; count1++){
     for(int count2=0; count2<size2 ; count2++){
        // How do i do this ?
        pointsArray............ =QPoint( count1, count2);

     ï
   }
   return pointsArray;
}

Thanks.

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Message 7 in thread

Hi

IMHO you are better off passing around a QList of QPairs

untested for illustration only:

typedef QPair<QPointF,QPointF> PointPair;
typedef QList<PointPair> PointPairList;

void fooFunction(&PointPairList theList)
{
   PointPair myPair;
   QPointF x;
   QPointF y;
   //do stuff to populate x and y....
   //
   myPair.first=x;
   myPair.second=y;
   theList.insert(myPair);
   //all done
}

I also avoid ** like the plague...

Regards

Tim

Em 22/05/2007, Ãs 08:53, hihihi escreveu:

> On Tuesday 22 May 2007 12:29, Peter Prade wrote:
>>> Over the years I have tried many times to understand the pointer
>>
>> stuff.
>>
>>> Part i understand and can use it.
>>> With the stuff below my mind goes blankertyblank
>>
>> [broken code that has many mistakes deleted]
>>
>> Which is another reason to leave the (dangerous and complicated)  
>> pointer
>> stuff alone. Use QVector or QList instead, and all will be fine :)
>>
>> const int size1=2000;
>> const int size2=50;
>>
>> class Cm {
>>   public:
>>     QVector<QVector<QPoint> > experiment();
>> };
>>
>> QVector<QVector<QPoint> > Cm::experiment()
>> {
>> 	QVector<QVector<QPoint> > pointsArray;
>> 	pointsArray.fill(QVector<QPoint>(size2),size1);
>
> On this line i get:
>  error: no matching function for call to  
> âQPtrVector<QPtrVector<QPoint>
>> ::fill(QPtrVector<QPoint>, const int&)â
> /usr/lib/qt-3.3/include/qptrvector.h:71: note: candidates are: bool
> QPtrVector<type>::fill(const type*, int) [with type =  
> QPtrVector<QPoint>]
> gmake[1]: *** [micrometer.o] Error 1
>
>
>> 	return pointsArray;
>> }
>
>
> How do i assign one qpoint to the qvectors ?
>
> QVector<QVector<QPoint> > Cm::experiment()
> {
>
>    QVector<QVector<QPoint> > pointsArray;
>    for(int count1=0; count1<size1 ; count1++){
>      for(int count2=0; count2<size2 ; count2++){
>         // How do i do this ?
>         pointsArray............ =QPoint( count1, count2);
>
>      ï
>    }
>    return pointsArray;
> }
>
> Thanks.
>
> --
> To unsubscribe - send a mail to qt-interest-request@xxxxxxxxxxxxx  
> with "unsubscribe" in the subject or the body.
> List archive and information: http://lists.trolltech.com/qt-interest/
>

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Message 8 in thread

> > > Over the years I have tried many times to understand the pointer
> >
> > stuff.
> >
> > > Part i understand and can use it.
> > > With the stuff below my mind goes blankertyblank
> >
> > [broken code that has many mistakes deleted]
> >
> > Which is another reason to leave the (dangerous and complicated)
pointer
> > stuff alone. Use QVector or QList instead, and all will be fine :)
> >
> > const int size1=2000;
> > const int size2=50;
> >
> > class Cm {
> >   public:
> >     QVector<QVector<QPoint> > experiment();
> > };
> >
> > QVector<QVector<QPoint> > Cm::experiment()
> > {
> > 	QVector<QVector<QPoint> > pointsArray;
> > 	pointsArray.fill(QVector<QPoint>(size2),size1);
> 
> On this line i get:
>  error: no matching function for call to
'QPtrVector<QPtrVector<QPoint>
> >::fill(QPtrVector<QPoint>, const int&)'
> /usr/lib/qt-3.3/include/qptrvector.h:71: note: candidates are: bool
> QPtrVector<type>::fill(const type*, int) [with type =
QPtrVector<QPoint>]
> gmake[1]: *** [micrometer.o] Error 1

dunno why gcc won't find the correct template, for me it compiles (on
MSVC)
you could try to typedef QVector<QPoint> and use that to help the
compiler.

or skip the use of fill and do it this way:

QVector<QVector<QPoint> > Cm::experiment()
{
   QVector<QVector<QPoint> > pointsArray(size1);
   for(int count1=0; count1<size1 ; count1++){
      pointsArray[count1].resize(size2);
      for(int count2=0; count2<size2 ; count2++){
         pointsArray[count1][count2] =QPoint( count1, count2);
      }
   }
   return pointsArray;
}

Cheers,
Peter

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Message 9 in thread

On Tuesday 22 May 2007 14:41, Peter Prade wrote:

> QVector<QVector<QPoint> > Cm::experiment()
> {
>    QVector<QVector<QPoint> > pointsArray(size1);
>    for(int count1=0; count1<size1 ; count1++){
>       pointsArray[count1].resize(size2);
>       for(int count2=0; count2<size2 ; count2++){
>          pointsArray[count1][count2] =QPoint( count1, count2);
>       }
>    }
>    return pointsArray;
> }

Compile gives two errors.

QVector< QVector < QPoint > > experiment5()
{
  typedef QVector<QPoint> VecPoint;

  QVector< VecPoint > pointsArray( size1);

  for(int count1=0; count1< size1 ; count1++){
    pointsArray[count1].resize( size2 );

This line gives this error:

m.cpp:738: error: request for member âresizeâ 
in âpointsArray.QPtrVector<type>::operator[] [with type = QPtrVector<QPoint>]
(count1)â, which is of non-class type âQPtrVector<QPoint>*â

    for(int count2=0; count2< size2 ; count2++){
      pointsArray[count1][count2]= QPoint( count1,count2);

   This line gives this error:

m.cpp:740: error: no match for âoperator=â in â*(pointsArray. 
QPtrVector<type>::operator[] [with type = QPtrVector<QPoint>](count1) + 
((QPtrVector<QPoint>*)(((unsigned int)count2) * 20u))) = QPoint(count1, 
count2)â
/usr/lib/qt-3.3/include/qptrvector.h:58: note: candidates are: 
QPtrVector<type>& QPtrVector<type>::operator=(const QPtrVector<type>&) [with 
type = QPoint]

    }
  }
  return pointsArray;
}


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Message 10 in thread

did you #include <QVector> ?

i'm sorry, maybe one of the gcc users can be of greater help to you.

Peter

> -----Original Message-----
> From: hihihi [mailto:hihihi@xxxxxxxxxx]
> Sent: Tuesday, May 22, 2007 6:07 PM
> To: qt-interest@xxxxxxxxxxxxx
> Subject: Re: How to make a function return a double array of qpoint ?
> 
> On Tuesday 22 May 2007 14:41, Peter Prade wrote:
> 
> > QVector<QVector<QPoint> > Cm::experiment()
> > {
> >    QVector<QVector<QPoint> > pointsArray(size1);
> >    for(int count1=0; count1<size1 ; count1++){
> >       pointsArray[count1].resize(size2);
> >       for(int count2=0; count2<size2 ; count2++){
> >          pointsArray[count1][count2] =QPoint( count1, count2);
> >       }
> >    }
> >    return pointsArray;
> > }
> 
> Compile gives two errors.
> 
> QVector< QVector < QPoint > > experiment5()
> {
>   typedef QVector<QPoint> VecPoint;
> 
>   QVector< VecPoint > pointsArray( size1);
> 
>   for(int count1=0; count1< size1 ; count1++){
>     pointsArray[count1].resize( size2 );
> 
> This line gives this error:
> 
> m.cpp:738: error: request for member 'resize'
> in 'pointsArray.QPtrVector<type>::operator[] [with type =
> QPtrVector<QPoint>]
> (count1)', which is of non-class type 'QPtrVector<QPoint>*'
> 
>     for(int count2=0; count2< size2 ; count2++){
>       pointsArray[count1][count2]= QPoint( count1,count2);
> 
>    This line gives this error:
> 
> m.cpp:740: error: no match for 'operator=' in '*(pointsArray.
> QPtrVector<type>::operator[] [with type = QPtrVector<QPoint>](count1)
+
> ((QPtrVector<QPoint>*)(((unsigned int)count2) * 20u))) =
QPoint(count1,
> count2)'
> /usr/lib/qt-3.3/include/qptrvector.h:58: note: candidates are:
> QPtrVector<type>& QPtrVector<type>::operator=(const QPtrVector<type>&)
> [with
> type = QPoint]
> 
>     }
>   }
>   return pointsArray;
> }
> 
> 
> --
> To unsubscribe - send a mail to qt-interest-request@xxxxxxxxxxxxx with
> "unsubscribe" in the subject or the body.
> List archive and information: http://lists.trolltech.com/qt-interest/

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Message 11 in thread

On Tuesday 22 May 2007 18:11, Peter Prade wrote:
> did you #include <QVector> ?

That does not work for me.
I use 
#include <qvector.h>

Which QT version are you thinking in ?
I use qt 3.3 on fedora core 6.

Perhaps 4.x works different ?

>
> i'm sorry, maybe one of the gcc users can be of greater help to you.

Thanks for trying :-)


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Message 12 in thread

Indeed i was assuming Qt4.

I still recommend using the container classes (or you might want to use
std::vector from the STL) - i just can't help you with code examples
there.

Cheers,
Peter

P.S.
It's a good idea to include the Qt version in the subject line!

> -----Original Message-----
> From: hihihi [mailto:hihihi@xxxxxxxxxx]
> Sent: Tuesday, May 22, 2007 6:41 PM
> To: qt-interest@xxxxxxxxxxxxx
> Subject: Re: How to make a function return a double array of qpoint ?
> 
> On Tuesday 22 May 2007 18:11, Peter Prade wrote:
> > did you #include <QVector> ?
> 
> That does not work for me.
> I use
> #include <qvector.h>
> 
> Which QT version are you thinking in ?
> I use qt 3.3 on fedora core 6.
> 
> Perhaps 4.x works different ?
> 
> >
> > i'm sorry, maybe one of the gcc users can be of greater help to you.
> 
> Thanks for trying :-)
> 
> 
> --
> To unsubscribe - send a mail to qt-interest-request@xxxxxxxxxxxxx with
> "unsubscribe" in the subject or the body.
> List archive and information: http://lists.trolltech.com/qt-interest/

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Message 13 in thread

On Tuesday 22 May 2007 18:52, Peter Prade wrote:
> Indeed i was assuming Qt4.

I am going to look into upgrading from qt 3.3 to qt 4.x


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Message 14 in thread

If you can do that, I would certainly recommend it simply because I find
Qt 4 to be quite intuitive.  If it's not, I can certainly try to help
you anyway or maybe someone with more experience with Qt 3 can help.

Along those lines, I took a peek at the Qt 3.3 API documentation, and
it's quite a bit different from Qt 4.  What you probably want to use in
Qt 3 is QValueVector since the QVector class is, well, not there :)  The
missing QVector class could possibly explain your problem, though I
couldn't say for sure without seeing your whole code file.

Good luck with the upgrade!

Stuart

> On Tuesday 22 May 2007 18:52, Peter Prade wrote:
>   
>> Indeed i was assuming Qt4.
>>     
>
> I am going to look into upgrading from qt 3.3 to qt 4.x
>
>
> --
> To unsubscribe - send a mail to qt-interest-request@xxxxxxxxxxxxx with "unsubscribe" in the subject or the body.
> List archive and information: http://lists.trolltech.com/qt-interest/
>
>

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Message 15 in thread

On Tuesday 22 May 2007 19:21, you wrote:
>  What you probably want to use in
> Qt 3 is QValueVector since the QVector class is, well, not there :)  The
> missing QVector class could possibly explain your problem, though I
> couldn't say for sure without seeing your whole code file.

QVector is in qt 3.3 called QPtrVector.
If you enter QVector it is automaticaly translated to QPtrVector.
I have relied on this auto translation in all my test of today.
Maybe there goes something wrong.

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