C++ template function compilation error

["Jinming Xu" <cybermanxu at hotmail dot com>]

Hello everyone,

I encountered a problem while compiling a C++ program which contains a 
built-in template function sort(). The source of the whole trouble is the 
statement as follows:

 sort(Int.begin(),Int.end());

where Int is a vector containing objects of a class which overloaded the 
operator<().

My program can be compiled with xlC_r successfully.  So I want to know 
whether gcc doesn't completely support template function or there are some 
switches I didn't turn on. The whole code is as follows:

//------code begins-----------------
#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

class Integer{
public:
 int i;
 Integer(int ii):i(ii){}
 bool operator<(Integer& other)
 {return this->i < other.i;}
};

int main()
{
 vector<Integer> Int;
 Int.push_back(Integer(5));
 Int.push_back(Integer(15));
 Int.push_back(Integer(0));

 sort(Int.begin(),Int.end());   // the source of trouble

 for(int k=0; k<Int.size();k++)
   cout<<Int[k].i<<endl;
}
//---------code ends--------------


The error messages I got were like this:

/usr/local/include/c++/3.3.3/bits/stl_algo.h: In function `const _Tp&
  std::__median(const _Tp&, const _Tp&, const _Tp&) [with _Tp = Integer]':
/usr/local/include/c++/3.3.3/bits/stl_algo.h:2120:   instantiated from `void 
std::__introsort_loop(_RandomAccessIter, _RandomAccessIter, _Size) [with 
_RandomAccessIter = __gnu_cxx::__normal_iterator<Integer*, 
std::vector<Integer, std::allocator<Integer> > >, _Size = long int]'
/usr/local/include/c++/3.3.3/bits/stl_algo.h:2180:   instantiated from `void 
std::sort(_RandomAccessIter, _RandomAccessIter) [with _RandomAccessIter = 
__gnu_cxx::__normal_iterator<Integer*, std::vector<Integer, 
std::allocator<Integer> > >]'main.cpp:21:   instantiated from here
/usr/local/include/c++/3.3.3/bits/stl_algo.h:90: error: no match for 
'operator<
  ' in '__a < __b'
... ...

Could any of you tell me what causes the failure of the compilation and how 
to fix it?

Any suggestions or hints will be appreciated!


Thanks in advance!



Jinming Xu

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