Re: How does std::set implement iterator through red black tree?
Fei Liu wrote:
This is a little more advanced topic. I am trying to understand why
erase on a set implemented through red black tree only invalidates the
iterator being erased? It'd seem to me when the RBTree needs to be
re-balanced, the ordering of iteration may change...What gives?
Fei
I took a reverse engineering approach by testing the blackbox
behavior...Here is what I got and something is a little unexpected here:
#include <set>
#include <iostream>
using namespace std;
void display(const set<int> & s){
cout << "node value: ";
set<int>::const_iterator it = s.begin();
for(;it != s.end(); ++it) cout << " " << *it;
cout << endl;
}
int main(){
set<int> s;
s.insert(4);
s.insert(1);
s.insert(10);
s.insert(2);
s.insert(3);
s.insert(5);
display(s);
s.erase(3);
display(s);
s.insert(3);
display(s);
cout << "node value: ";
set<int>::const_iterator it = s.begin();
while(it != s.end()){
if(*it == 3) s.erase(it++);
else ++it;
if(it != s.end()) cout << " " << *it;
}
cout << endl;
display(s);
}
../test_set_iter
node value: 1 2 3 4 5 10
node value: 1 2 4 5 10
node value: 1 2 3 4 5 10
node value: 2 3 4 5 10
node value: 1 2 4 5 10
It seems like although erase is done correctly but I am getting a '3' in
the fourth row of output. There seems be a incoherence between the
iterator and the state of the iteration...The red black tree is lying at
what node it's currently traversing the tree?!
Fei
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