可能重复：
与自己的班级交友“>>”
我正在尝试将 '<' 运算符与我自己的类交朋友，但它没有注意到我的语法错误，但我得到了以下编译错误：
错误：
**** 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]
类和重载函数：
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;
}
};
是否出现错误（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;
}
}