Vector of Classes w/ overloaded operators notcompiling

[somgoozy]

I am working on a school project and am stuck in the debugging. I am compiling with g++ and am using c++11.

Error message

 
In file included from /usr/include/c++/4.7/algorithm:63:0,
                 from date.h:7,
                 from date.cpp:1,
                 from schedule.h:1,
                 from schedule.cpp:1,
                 from date_driver.cpp:1:
/usr/include/c++/4.7/bits/stl_algo.h: In instantiation of ‘_RandomAccessIterator std::__unguarded_partition(_RandomAccessIterator, _RandomAccessIterator, const _Tp&) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<Date*, std::vector<Date> >; _Tp = Date]’:
/usr/include/c++/4.7/bits/stl_algo.h:2309:70:   required from ‘_RandomAccessIterator std::__unguarded_partition_pivot(_RandomAccessIterator, _RandomAccessIterator) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<Date*, std::vector<Date> >]’
/usr/include/c++/4.7/bits/stl_algo.h:2340:54:   required from ‘void std::__introsort_loop(_RandomAccessIterator, _RandomAccessIterator, _Size) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<Date*, std::vector<Date> >; _Size = int]’
/usr/include/c++/4.7/bits/stl_algo.h:5476:4:   required from ‘void std::sort(_RAIter, _RAIter) [with _RAIter = __gnu_cxx::__normal_iterator<Date*, std::vector<Date> >]’
schedule.cpp:92:50:   required from here
/usr/include/c++/4.7/bits/stl_algo.h:2271:4: error: passing ‘const Date’ as ‘this’ argument of ‘bool Date::operator<(Date)’ discards qualifiers [-fpermissive]

I have a vector of a date class that I am trying to sort within another class and this is my sort function that is giving me an error.

      
    void schedule :: sortDates (){
        sort (mustRemember.begin (), mustRemember.end ());
    }

Here are my overloaded operators for my date class.

    bool Date :: operator == (Date otherDate){
    		if (((otherDate.getDay () == getDay ()) && (otherDate.getMonth () == getMonth ())) && (otherDate.getYear () == getYear ()))
    			return true;
    		else
    			return false;
    }

    bool Date :: operator < (Date otherDate){
    		if (getYear () < otherDate.getYear ())
    			return true;
    		else if (getYear () > otherDate.getYear ())
    			return false;
    		else if (getMonth () < otherDate.getMonth ())
    			return true;
    		else if (getMonth () > otherDate.getMonth ())
    			return false;
    		else if (getDay () < otherDate.getDay ())
    			return true;
    		else
	    		return false;
    }

Let me know if I should include any more information.

[ne555]

your problem is const-correctness.
mark any member function that does not modify the sate of the object as const