std::set using class pointers. How to control insert [duplicate]

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• error: passing xxx as 'this' argument of xxx discards qualifiers 3 answers

I have been google all over the place and am unable to find a working example for how to use std::set and control the insert order. I found comments for my type of structure but I get a compile error.

I am trying to sort on myMaskName so I get

  address  class
0x19ec220 TEST1 2 26
0x19eba90 TEST2 100 26
0x19ebb00 TEST3 230 26
0x19eba20 TEST4 240 26

vs. this default order

0x19eba20 TEST4 240 26
0x19eba90 TEST2 100 26
0x19ebb00 TEST3 230 26
0x19ec220 TEST1 2 26

This is my test code:

class FoIxCompareMaskNew
{
public:
        // Main constructor.
        FoIxCompareMaskNew (const char *maskName,  const int&  startAddress, const int& numWords) :
                myMaskName(maskName),
                myStartAddress(startAddress),
                myNumberWords(numWords)
        {
        }

    ~FoIxCompareMaskNew ();

    std::string MaskName() {return myMaskName;}
    int StartAddress() {return myStartAddress;}
    int NumberWords() {return myNumberWords;}

private:

    std::string myMaskName;
    int     myStartAddress;
    int     myNumberWords;
};

struct FoIxCompareMaskNewComp {
    bool operator()(const FoIxCompareMaskNew* p_lhs, const FoIxCompareMaskNew* p_rhs) const
    {
        std::string temp = p_lhs->MaskName();
        return temp.compare(p_rhs->MaskName());
    }
};

void newWay()
{
    std::multiset<FoIxCompareMaskNew *, FoIxCompareMaskNewComp> maskList;
    std::multiset<FoIxCompareMaskNew *, FoIxCompareMaskNewComp> maskList2;
    FoIxCompareMaskNew * list[4];

    list[0] = new FoIxCompareMaskNew("TEST1", 2, 26);
    list[2] = new FoIxCompareMaskNew("TEST3", 230, 26);
    list[1] = new FoIxCompareMaskNew("TEST2", 100, 26);
    list[3] = new FoIxCompareMaskNew("TEST4", 240, 26);

maskList.insert(list[0] );
    maskList.insert(list[1] );
    maskList2.insert(list[0] );
    maskList2.insert(list[1] );
    maskList2.insert(list[2] );
    maskList2.insert(list[3] );
}

int main(int, char**)
{
    newWay();
}

This is the error I see on compile. It doesn't like me accessing the members.

./main.C: In member function ‘bool FoIxCompareMaskNewComp::operator()(const FoIxCompareMaskNew*, const FoIxCompareMaskNew*) const’:
./main.C:205:38: error: passing ‘const FoIxCompareMaskNew’ as ‘this’ argument of ‘std::string FoIxCompareMaskNew::MaskName()’ discards qualifiers [-fpermissive]
   std::string temp = p_lhs->MaskName();
                                      ^
./main.C:206:39: error: passing ‘const FoIxCompareMaskNew’ as ‘this’ argument of ‘std::string FoIxCompareMaskNew::MaskName()’ discards qualifiers [-fpermissive]
   return temp.compare(p_rhs->MaskName());

All the examples I have founder are for int or std::string. I have found no example of someone using a class like this beyond saying setup a compare struct and use that.

So what am I doing wrong?