qSort() problem

[darksaga]

hi all,

I have a strange prob to sort my QList with the qSort() function.

the class to be sorted looks like:

#ifndef MYCLASS_H
#define MYCLASS_H
 
class MyClass{
	public:
            MyClass(){}
            ~MyClass{}
            bool operator<(const MyClass& a) const {
			return getBpCount() < a.getBpCount();
		     } 
            const float getBpCount(void) const{return /*some calculated float*/;}
}
#endif

#ifndef MYCLASS_H
#define MYCLASS_H

class MyClass{
	public:
            MyClass(){}
            ~MyClass{}
            bool operator<(const MyClass& a) const {
			return getBpCount() < a.getBpCount();
		     } 
            const float getBpCount(void) const{return /*some calculated float*/;}
}
#endif

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in the class, where I use the class above, I do the following:

QList<MyClass*> *list = new QList<MyClass*>;
for(){/*create new MyClasses & add to list*/}
 
//finally
//checked the listorder here1
qSort(*list);
//and here2

QList<MyClass*> *list = new QList<MyClass*>;
for(){/*create new MyClasses & add to list*/}

//finally
//checked the listorder here1
qSort(*list);
//and here2

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the list should be sorted, but it isn't

there is some change between here1 & here2 but @ here2 the list isn't oredered in an ascending or descending order, it seems to be random to me

can anybody tell me what I'm missing or doing wrong???

regards

[jpn]

The list gets sorted by pointer values. You should store objects (eg. QList<MyClass>) to get it sorted like you want.

[jpn]

Oh, and by the way. Actually you can sort pointers too with the help of custom comparator function:

bool myClassLessThan(const MyClass* a, const MyClass* b)
{
	return a->getBpCount() < b->getBpCount();
}
 
qSort(list->begin(), list->end(), myClassLessThan);

bool myClassLessThan(const MyClass* a, const MyClass* b)
{
	return a->getBpCount() < b->getBpCount();
}

qSort(list->begin(), list->end(), myClassLessThan);

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As a side note, QList is an implicitly shared class so usually it's allocated on stack.

[darksaga]

ok,
this explains the "random" order after using the qSort funcion

did it the way u suggested, and tried to use the lessThan function, but now my compiler starts to bitch around

if the lessThan function is defined in MyClass, the compiler says:

error c2065: 'myClassLessThan': unknown identifier

if I declare lessThan in the class, where i use the qSort function, it says:

moc_ResultContainer.cpp
..\..\qt4\include\QtCore\qalgorithms.h(359) : error C2064: Ausdruck ergibt keine Funktion, die 2 Argumente übernimmt
..\..\qt4\include\QtCore\qalgorithms.h(184): Siehe Verweis auf Instanziierung der kompilierten Funktionsvorlage 'void QAlgorithmsPrivate::qSortHelper<RandomAccessIterat or,T,LessThan>(RandomAccessIterator,RandomAccessIt erator,const T & ,LessThan)'
with
[
RandomAccessIterator=QList<MyClass *>::iterator,
T=MyClass *,
LessThan=bool (__thiscall ResultContainer::* )(const MyClass *,const MyClass *)
]
c:\devel\projects\projekt_main_vs\release\../src\Workbench\ResultContainer.h(56): Siehe Verweis auf Instanziierung der kompilierten Funktionsvorlage 'void qSort<QList<T>::iterator,bool(__thiscall ResultContainer::* )(const MyClass *,const MyClass *)>(RandomAccessIterator,RandomAccessIterator,Less Than)'
with
[
T=MyClass *,
RandomAccessIterator=QList<MyClass *>::iterator,
LessThan=bool (__thiscall ResultContainer::* )(const MyClass *,const MyClass *)
]
..\..\qt4\include\QtCore\qalgorithms.h(364) : error C2064: Ausdruck ergibt keine Funktion, die 2 Argumente übernimmt
..\..\qt4\include\QtCore\qalgorithms.h(366) : error C2064: Ausdruck ergibt keine Funktion, die 2 Argumente übernimmt
..\..\qt4\include\QtCore\qalgorithms.h(374) : error C2064: Ausdruck ergibt keine Funktion, die 2 Argumente übernimmt

so, what is it now, that I'm missing?

[jpn]

You are passing a function pointer so the function must be

• either declared as static member function
• or declared in the global namespace (not a member function)

For more details, see C++ FAQ LITE: [33] Pointers to member functions.

[darksaga]

You are passing a function pointer so the function must be

• either declared as static member function
• or declared in the global namespace (not a member function)

For more details, see C++ FAQ LITE: [33] Pointers to member functions.

makes sense , though I don't like static & global declared stuff...

works like a charm now, thanks alot jpn