error calling pointer to member function in c++

Question

class Solution {
public:
    bool cmp(pair<int, int>& aa,pair<int, int>& bb){
        if(aa.first<bb.first) return true;
        else if(aa.second<bb.second) return true;
        else return false;
    }
    int maxEnvelopes(vector<pair<int, int> >& envelopes) {
        int i,sz;
        sz=envelopes.size();
        vector<int> v1,v2;
        vector<int>::iterator it1;
        vector<int>::iterator it2;
        sort(envelopes.begin(),envelopes.end(),cmp);
        for(i=0;i<sz;i++){
            it1=lower_bound(v1.begin(),v1.end(),envelopes[i].first);
            it2=lower_bound(v2.begin(),v2.end(),envelopes[i].second);
            if(it1==v1.end()&&it2==v2.end()){
                v1.push_back(envelopes[i].first);
                v2.push_back(envelopes[i].second);
            }
            else{
                v1[it1-v1.end()]=envelopes[i].first;
                v2[it2-v2.end()]=envelopes[i].second;
            }
            //cout<<v1.size()<<" "<<v2.size()<<endl;
        }
        return v1.size();
    }
};

I am getting "error: must use '.*' or '->*' to call pointer-to-member function" And it redirects me to predefined_ops.h file when I compile code in codeblocks compiler.

First of all, where do you get the error? Please mark it out with a comment or something like that. Secondly, does the cmp function really need to be a member function? And why isn't it a static member function? — Some programmer dude
– Some programmer dude, Commented Aug 26, 2016 at 4:36
Thanks a lot :) . After using static member function it is working now. — Shaikh Hafiz Ahamed
– Shaikh Hafiz Ahamed, Commented Aug 26, 2016 at 4:50
Whole page of useful information on pointers to member functions. Also look at std::function and std::bind — user4581301
– user4581301, Commented Aug 26, 2016 at 4:57

R Sahu · Accepted Answer · 2016-08-26 04:49:42Z

3

You cannot use a non-static member function, such as cmp, as an argument to sort.

The argument to sort has to be a global function, a static member function, or a callable object.

Make cmp a static member function for your program to work.

answered Aug 26, 2016 at 4:49

R Sahu

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