Sort QList of pointers

[giantdragon]

I have a QList of QTcpSocket derived class pointers, which have a custom field for transfer speed and I need to sort list by this field. It is easy to use function qSort for list of values, but I haven't found how not apply this func for list of pointers.

[joyer83]

Maybe you could use this version of the qSort?

void qSort ( RandomAccessIterator begin, RandomAccessIterator end, LessThan lessThan )

void qSort ( RandomAccessIterator begin, RandomAccessIterator end, LessThan lessThan )

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And use your own less than comparison function where you compare the fields.

[giantdragon]

Maybe you could use this version of the qSort?

void qSort ( RandomAccessIterator begin, RandomAccessIterator end, LessThan lessThan )

void qSort ( RandomAccessIterator begin, RandomAccessIterator end, LessThan lessThan )

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And use your own less than comparison function where you compare the fields.

I know about this method, but I don't know how to correctly write this function for accepting pointers.

bool lessThan(MyClass *first, MyClass *second)

bool lessThan(MyClass *first, MyClass *second)

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Doesn't work.

[wysota]

Seems to work fine for me:

#include <QtCore>
 
struct A {
 A(int _x) : x(_x){}
 int x;
};
 
bool lessThan(A *one, A*two){
  return one->x < two->x;
}
 
int main(int argc, char **argv){
  QList<A*> list;
  for(int i=0;i<100;++i){
    list << new A(qrand()%1000);
  }
  qSort(list.begin(), list.end(), lessThan);
  foreach(A *it, list) qDebug() << it->x;
  return 0;
}

#include <QtCore>

struct A {
 A(int _x) : x(_x){}
 int x;
};

bool lessThan(A *one, A*two){
  return one->x < two->x;
}

int main(int argc, char **argv){
  QList<A*> list;
  for(int i=0;i<100;++i){
    list << new A(qrand()%1000);
  }
  qSort(list.begin(), list.end(), lessThan);
  foreach(A *it, list) qDebug() << it->x;
  return 0;
}

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[giantdragon]

Finally I found solution: just need to add STATIC keyword to function's declaration, e.g. for descending sort:

Header:

static bool compareSockets(ClientSocket *first, ClientSocket *second);

static bool compareSockets(ClientSocket *first, ClientSocket *second);

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CPP:

bool NetworkManager::compareSockets(ClientSocket *first, ClientSocket *second)
{
    return first->getTransferSpeed() > second->getTransferSpeed();
}

bool NetworkManager::compareSockets(ClientSocket *first, ClientSocket *second)
{
    return first->getTransferSpeed() > second->getTransferSpeed();
}

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Call:

qSort(clientList->begin(), clientList->end(), compareSockets);

qSort(clientList->begin(), clientList->end(), compareSockets);

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[wysota]

Finally I found solution: just need to add STATIC keyword to function's declaration

It's a method not a function. That's your problem -- lessThan is supposed to be a function.