Why '<' is forbidden for SET's iterator?Code:int tmp[]={3,2,1,3,2,4,5,4,2}; vector<int> vc(tmp,tmp+9); set<int> st(vc.begin(), vc.end()); vector<int>::iterator vit=vc.begin(); for(;vit<vc.end();it++) cout<<*it<<' '; // OK set<int>::iterator sit=st.begin(); for(;sit<st.end();it++) cout<<*it<<' '; // Error for(;sit!=st.end();it++) cout<<*it<<' '; // OK