Sorting a QList with a Comparator

reactive

Hi, I'm trying to implement sort() in my QAbstractTableModel and I'm having some problems.
The underlying rows are a QList<Foo*>, where I use a class to map Foo fields to table columns.

I tried to use qSort(rows.start(), rows.end(), lessThan) but the lessThan function has to be a
static or global function so I'm not sure how to pass the column number to it?

Also, the doc says: "Note that earlier versions of Qt allowed using a lessThan function that took its arguments by non-const reference. From 4.3 and on this is no longer possible, the arguments has to be passed by const reference or value."
In this case I have pointers.

Is there a way to sort with something like Java's Comparator (an "interface" with a compare function that takes 2 templated types)?

dangelog

qSort also accepts a functionoid as 3rd argument, which means an object of any class with a proper bool operator()(const T &t1, const T &t2) (true means that t1 < t2 in the sorting order).

goetz

A sample to achieve this:

-- test.h --

@
class QDebug;

class Foo {
public:
friend class FooLessThan;
friend QDebug operator<<(QDebug dbg, const Foo &foo);
friend QDebug operator<<(QDebug dbg, const Foo *foo);
Foo(int f, int g, int h);

protected:
int _f;
int _g;
int _h;
};

QDebug operator<<(QDebug dbg, const Foo &foo);
QDebug operator<<(QDebug dbg, const Foo *foo);

class FooLessThan
{
public:
FooLessThan( int column );
bool operator()(const Foo *left, const Foo *right ) const;

private:
int _column;
};
@

-- test.cpp --
@
#include "test.h"

#include <QDebug>

Foo::Foo(int f, int g, int h)
{
_f = f;
_g = g;
_h = h;
}

QDebug operator<<(QDebug dbg, const Foo &foo)
{
return operator<<(dbg, &foo);
}

QDebug operator<<(QDebug dbg, const Foo foo)
{
if(foo)
dbg.nospace() << "Foo(" << (void)foo << ")[f=" << foo->_f << ", g=" << foo->_g << " h=" << foo->_h << "]";
else
dbg.nospace() << "Foo(null)";
return dbg.space();
}

FooLessThan::FooLessThan( int column )
: _column( column )
{
}

bool FooLessThan::operator()(const Foo *left, const Foo *right ) const
{
switch(_column) {
case 1: return left->_f < right->_h;
case 2: return left->_f < right->_g;
case 3: return left->_h < right->_h;
default: return left->_f < right->_h;
}
}
@

-- main.cpp --

@
#include <QList>
#include <QDebug>

#include "test.h"

int main(int argc, char *argv[])
{
QList<Foo *> fooList;
fooList << new Foo(1, 2, 3);
fooList << new Foo(30, 20, 10);
fooList << new Foo(9, 8, 1);

qDebug() << fooList;
FooLessThan flt(1);

qSort(fooList.begin(), fooList.end(), FooLessThan(1));
qDebug() << fooList;

qSort(fooList.begin(), fooList.end(), FooLessThan(2));
qDebug() << fooList;

qSort(fooList.begin(), fooList.end(), FooLessThan(3));
qDebug() << fooList;

return 0;

}
@

reactive

You guys are awesome. Thanks so much. I didn't realize I could pass a functor.
I had gotten an error before that led me to a StackOverflow posts that said you
couldn't use member functions.