error deleting item from list after passing through function - c++

Question

I'm having a bit of trouble understanding what's happening when I try to delete an element from a list in this program i'm working on.
#include <cmath>
#include <cstdio>
#include <list>
#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;
int findHigherSkillLevel(int skillLevel, list<int>::iterator *it, list<int> &list) {
if (it == NULL) return 0;
if (**it == (skillLevel + 1)) {
it = list.erase(it);
return 1 + findHigherSkillLevel(**it, it, list) + findHigherSkillLevel(**it, --it, list);
}
return 0;
}
int findLowerSkillLevel(int skillLevel, list<int>::iterator *it, list<int> &list) {
if (it == NULL) return 0;
if (**it == (skillLevel - 1)) {
it = list.erase(it);
return 1 + findLowerSkillLevel(**it, it, list) + findLowerSkillLevel(**it, --it, list);
}
return 0;
}
int findGroupsSizes(int skillLevel, list<int>::iterator *it, list<int> &list) {
if (it == NULL) return 0;
int groupSize = 1;
it = list.erase(it);
groupSize += findHigherSkillLevel(**it, it, list) + findLowerSkillLevel(**it, it, list);
return groupSize;
}
int main() {
int t; // the number of test cases
cin >> t;
vector<list<int> > skillLevels(t, list<int>());
// input for each test case
for (int i = 0; i < t; i++) {
int n; // number of students for this test case
cin >> n;
// initialize the list for this test case
for (int j = 0; j < n; j++) {
int skillLevel;
cin >> skillLevel;
skillLevels[i].push_back(skillLevel);
}
}
// recursively scan lists for smallest teams
for (int i = 0; i < t; i++) {
int minGroupNumber = skillLevels[i].size();
list<int>::iterator iterator = skillLevels[i].begin();
int skillLevel = skillLevels[i].front();
while (!skillLevels[i].empty()) {
int currentGroupSize = findGroupsSizes(skillLevel, &iterator, skillLevels[i]);
if (currentGroupSize < minGroupNumber)
minGroupNumber = currentGroupSize;
skillLevels[i].pop_front();
}
cout << minGroupNumber << endl;
}
return 0;
}
I already know that what's causing the error trying to call the "erase" function like this:
it = list.erase(it);
Which I typed in bold in the code. I don't understand why it's giving me the following output, since from what I understand erase() just needs an iterator to the location of the list to be deleted?:
teamFormation.cpp: In function ‘int findHigherSkillLevel(int, std::list<int>::iterator*, std::list<int>&)’:
teamFormation.cpp:13:24: error: no matching function for call to ‘std::list<int>::erase(std::list<int>::iterator*&)’
it = *list.erase(it);
^
teamFormation.cpp:13:24: note: candidates are:
In file included from /usr/include/c++/4.8/list:64:0,
from teamFormation.cpp:3:
/usr/include/c++/4.8/bits/list.tcc:108:5: note: std::list<_Tp, _Alloc>::iterator std::list<_Tp, _Alloc>::erase(std::list<_Tp, _Alloc>::iterator) [with _Tp = int; _Alloc = std::allocator<int>; std::list<_Tp, _Alloc>::iterator = std::_List_iterator<int>]
list<_Tp, _Alloc>::
^
/usr/include/c++/4.8/bits/list.tcc:108:5: note: no known conversion for argument 1 from ‘std::list<int>::iterator* {aka std::_List_iterator<int>*}’ to ‘std::list<int>::iterator {aka std::_List_iterator<int>}’
In file included from /usr/include/c++/4.8/list:63:0,
from teamFormation.cpp:3:
/usr/include/c++/4.8/bits/stl_list.h:1193:7: note: std::list<_Tp, _Alloc>::iterator std::list<_Tp, _Alloc>::erase(std::list<_Tp, _Alloc>::iterator, std::list<_Tp, _Alloc>::iterator) [with _Tp = int; _Alloc = std::allocator<int>; std::list<_Tp, _Alloc>::iterator = std::_List_iterator<int>]
erase(iterator __first, iterator __last)
^
/usr/include/c++/4.8/bits/stl_list.h:1193:7: note: candidate expects 2 arguments, 1 provided
teamFormation.cpp: In function ‘int findLowerSkillLevel(int, std::list<int>::iterator*, std::list<int>&)’:
teamFormation.cpp:24:24: error: no matching function for call to ‘std::list<int>::erase(std::list<int>::iterator*&)’
it = *list.erase(it);
^
teamFormation.cpp:24:24: note: candidates are:
In file included from /usr/include/c++/4.8/list:64:0,
from teamFormation.cpp:3:
/usr/include/c++/4.8/bits/list.tcc:108:5: note: std::list<_Tp, _Alloc>::iterator std::list<_Tp, _Alloc>::erase(std::list<_Tp, _Alloc>::iterator) [with _Tp = int; _Alloc = std::allocator<int>; std::list<_Tp, _Alloc>::iterator = std::_List_iterator<int>]
list<_Tp, _Alloc>::
^
/usr/include/c++/4.8/bits/list.tcc:108:5: note: no known conversion for argument 1 from ‘std::list<int>::iterator* {aka std::_List_iterator<int>*}’ to ‘std::list<int>::iterator {aka std::_List_iterator<int>}’
In file included from /usr/include/c++/4.8/list:63:0,
from teamFormation.cpp:3:
/usr/include/c++/4.8/bits/stl_list.h:1193:7: note: std::list<_Tp, _Alloc>::iterator std::list<_Tp, _Alloc>::erase(std::list<_Tp, _Alloc>::iterator, std::list<_Tp, _Alloc>::iterator) [with _Tp = int; _Alloc = std::allocator<int>; std::list<_Tp, _Alloc>::iterator = std::_List_iterator<int>]
erase(iterator __first, iterator __last)
^
/usr/include/c++/4.8/bits/stl_list.h:1193:7: note: candidate expects 2 arguments, 1 provided
teamFormation.cpp: In function ‘int findGroupsSizes(int, std::list<int>::iterator*, std::list<int>&)’:
teamFormation.cpp:35:22: error: no matching function for call to ‘std::list<int>::erase(std::list<int>::iterator*&)’
it = *list.erase(it);
^
teamFormation.cpp:35:22: note: candidates are:
In file included from /usr/include/c++/4.8/list:64:0,
from teamFormation.cpp:3:
/usr/include/c++/4.8/bits/list.tcc:108:5: note: std::list<_Tp, _Alloc>::iterator std::list<_Tp, _Alloc>::erase(std::list<_Tp, _Alloc>::iterator) [with _Tp = int; _Alloc = std::allocator<int>; std::list<_Tp, _Alloc>::iterator = std::_List_iterator<int>]
list<_Tp, _Alloc>::
^
/usr/include/c++/4.8/bits/list.tcc:108:5: note: no known conversion for argument 1 from ‘std::list<int>::iterator* {aka std::_List_iterator<int>*}’ to ‘std::list<int>::iterator {aka std::_List_iterator<int>}’
In file included from /usr/include/c++/4.8/list:63:0,
from teamFormation.cpp:3:
/usr/include/c++/4.8/bits/stl_list.h:1193:7: note: std::list<_Tp, _Alloc>::iterator std::list<_Tp, _Alloc>::erase(std::list<_Tp, _Alloc>::iterator, std::list<_Tp, _Alloc>::iterator) [with _Tp = int; _Alloc = std::allocator<int>; std::list<_Tp, _Alloc>::iterator = std::_List_iterator<int>]
erase(iterator __first, iterator __last)
^
/usr/include/c++/4.8/bits/stl_list.h:1193:7: note: candidate expects 2 arguments, 1 provided

Answer 1

The error message is self-explanatory: at that point it is not a std::list::iterator, it's actually an std::list::iterator*. You must dereference the pointer (as you did just on the previous line).