friend/overload '<' with own class [duplicate] - c++

Question

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Closed 10 years ago.
Possible Duplicate:
Friending '>>' with own class
I'm trying to friend '<' operator with my own class but it doesn't notice me about an syntax error, but i get the fallowing compile error:
error:
**** Internal Builder is used for build ****
g++ -O0 -g3 -Wall -c -fmessage-length=0 -o main.o ..\main.cpp
In file included from c:\mingw\bin\../lib/gcc/mingw32/4.6.1/include/c++/algorithm:63:0,
from ..\main.cpp:8:
c:\mingw\bin\../lib/gcc/mingw32/4.6.1/include/c++/bits/stl_algo.h: In function '_RandomAccessIterator std::__unguarded_partition(_RandomAccessIterator, _RandomAccessIterator, const _Tp&) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<RAngle*, std::vector<RAngle> >, _Tp = RAngle]':
c:\mingw\bin\../lib/gcc/mingw32/4.6.1/include/c++/bits/stl_algo.h:2253:70: instantiated from '_RandomAccessIterator std::__unguarded_partition_pivot(_RandomAccessIterator, _RandomAccessIterator) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<RAngle*, std::vector<RAngle> >]'
c:\mingw\bin\../lib/gcc/mingw32/4.6.1/include/c++/bits/stl_algo.h:2284:54: instantiated from 'void std::__introsort_loop(_RandomAccessIterator, _RandomAccessIterator, _Size) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<RAngle*, std::vector<RAngle> >, _Size = int]'
c:\mingw\bin\../lib/gcc/mingw32/4.6.1/include/c++/bits/stl_algo.h:5330:4: instantiated from 'void std::sort(_RAIter, _RAIter) [with _RAIter = __gnu_cxx::__normal_iterator<RAngle*, std::vector<RAngle> >]'
..\main.cpp:13:24: instantiated from here
c:\mingw\bin\../lib/gcc/mingw32/4.6.1/include/c++/bits/stl_algo.h:2215:4: error: passing 'const RAngle' as 'this' argument of 'bool RAngle::operator<(RAngle)' discards qualifiers [-fpermissive]
class and overload function:
class RAngle
{
public:
int x,y,l;
int solution,prec;
RAngle(){
}
RAngle(int i,int j,int k){
x=i,y=j,l=k;
}
bool operator<(const RAngle rhs)
{
if(l < rhs.l){
return true;
}
return 0;
}
};
Were error appears(main.cpp):
void descrSort(vector <RAngle> &l){
sort(l.begin(),l.end());
reverse(l.begin(),l.end());
for(unsigned i=0; i<l.size();i++){
cout<<l[i]<<endl;
}
}

Answer 1

Couldn't this have been added to your last question on this subject?
bool operator<(const RAngle rhs)
should be
bool operator<(const RAngle& rhs) const
which should fix the error. It is a good habit to mark methods which do not modify state as const.