Compilation error for template class - c++

Question

I'm beginer in templates and cann't resolve one compiler issue. The problem is in the following:
I have two classes.
class TMessage
{
public:
int Priority;
TMessageType Type;
bool operator> (const TMessage& m)
{
return m.Priority > Priority;
}
bool operator< (const TMessage& m)
{
return m.Priority < Priority;
}
};
template<typename T> class TMessageQueue
{
public:
T* Buffer;
int QueueStartOffset;
void SortMessages(int putPointer)
{
std::sort(Buffer+QueueStartOffset,Buffer+ putPointer);
}
};
In file included from /usr/include/c++/4.8/algorithm:62:0,
from TMessageQueue.h:2,
from TWriterThread.h:2,
from TWriterThread.cpp:1:
/usr/include/c++/4.8/bits/stl_algo.h: In instantiation of ‘_RandomAccessIterator std::__unguarded_partition(_RandomAccessIterator, _RandomAccessIterator, const _Tp&) [with _RandomAccessIterator = TMessage*; _Tp = TMessage]’:
/usr/include/c++/4.8/bits/stl_algo.h:2283:70: required from ‘_RandomAccessIterator std::__unguarded_partition_pivot(_RandomAccessIterator, _RandomAccessIterator) [with _RandomAccessIterator = TMessage*]’
/usr/include/c++/4.8/bits/stl_algo.h:2315:54: required from ‘void std::__introsort_loop(_RandomAccessIterator, _RandomAccessIterator, _Size) [with _RandomAccessIterator = TMessage*; _Size = long int]’
/usr/include/c++/4.8/bits/stl_algo.h:5461:36: required from ‘void std::sort(_RAIter, _RAIter) [with _RAIter = TMessage*]’
TMessageQueue.h:158:60: required from ‘void TMessageQueue::SortMessages(int) [with T = TMessage]’
TMessageQueue.h:143:26: required from ‘TRetCode TMessageQueue::Put(T&) [with T = TMessage]’
TWriterThread.cpp:59:34: required from here
/usr/include/c++/4.8/bits/stl_algo.h:2245:19: error: passing ‘const TMessage’ as ‘this’ argument of ‘bool TMessage::operator<(const TMessage&)’ discards qualifiers [-fpermissive]
while (__pivot < *__last)
^
make: *** [all] Error 1
What is the problem? Used compiler g++.

Answer 1

The operator< and operator> methods need to be const
bool operator> (const TMessage& m) const { ... }
bool operator< (const TMessage& m) const { ... }

Answer 2

In addition the first answer by simpel01,
this bad code:
bool operator> (const TMessage& m)
{
return m.Priority > Priority;
}
bool operator< (const TMessage& m)
{
return m.Priority < Priority;
}
In operator > must return this->Priority > m.Priority not m.Priority > this->Priority because operator > activated by object this and actually you want to say if I'm (object this) big than from m.
what you do is reverse!
and fix operator < to this->Priority < m.Priority