Problem sorting a list of pointers

Question

i am trying to sort a list of pointers (in my case each pointer is of type Job) my intention is to sort the jobs by their serial number

void Container::jobSort(list<Job*> &jobs) {
    sort(jobs.begin(), jobs.end(), jobSerialCompare);
 }

bool Container::jobSerialCompare(const Job *jobA,const Job *jobB) {

   return (jobA->getSn()<jobB->getSn());
 }

the error i'm getting is :

error: no matching function for call to 'sort(std::_List_iterator<Job*>, std::_List_iterator<Job*>, <unresolved overloaded function type>)'
/usr/include/c++/4.2.1/bits/stl_algo.h:2852: note: candidates are: void std::sort(_RandomAccessIterator, _RandomAccessIterator, _Compare) [with _RandomAccessIterator = std::_List_iterator<Job*>, _Compare = bool (Container::*)(const Job*, const Job*)]
make: *** [src/Container.o] Error 1

i managed to solve the error by changing the code as follows :

struct compare {
  bool operator()(const Job *jobA, const Job *jobB) {    return (jobA->getSn()<jobB->getSn());
 }
};

 void Container::jobSort(list<Job*> &jobs) {
    jobs.sort(compare());
 }

no compilation error now but i'm wondering what is wrong with my initial steps, help is appreciated, cheers

EDIT - Thanks a lot for all the help everyone ! all the different answers helped paint a clearer picture

Yakov Galka · Accepted Answer · 2010-12-05 15:55:38Z

3

The error message says it all. You are trying to sort a list with a sort() that expects a random access iterators. List supports only bidirectional iterators, so the stand-alone sort() doesn't work. That's why you must use a specific algorithms for lists: list.sort();

Also others spotted the non-static comparator issue, which is unrelated to the message you've got (but still must be fixed).

answered Dec 5, 2010 at 15:55

Yakov Galka

72.8k16 gold badges148 silver badges226 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

VinS · Accepted Answer · 2010-12-05 16:02:22Z

2

In the first case Container::jobSerialCompare is a member function. You should convert member function to function object with a mem_fun function in order to use it with sort. Try to write

#include <functional>
...
void Container::jobSort(list<Job*> &jobs) {
sort(jobs.begin(), jobs.end(), mem_fun(&Container::jobSerialCompare));

}

answered Dec 5, 2010 at 16:02

VinS

1941 silver badge8 bronze badges

Comments

davka · Accepted Answer · 2010-12-05 16:45:08Z

2

in your first version the Container::jobSerialCompare is a member function so it has an implicit first parameter of this, and so it does not fit to what std::sort() expects. The way to solve this is either to define the function in the global scope, or to define a functor, i.e. a class with operator()(), as you did.

EDIT: ... or to use mem_fun as VinS suggests

edited Dec 5, 2010 at 16:45

answered Dec 5, 2010 at 15:52

davka

14.9k13 gold badges67 silver badges88 bronze badges

Collectives™ on Stack Overflow

Problem sorting a list of pointers

3 Answers 3

Comments

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related