C++ template function compilation error

[Jinming Xu]

llewelly,

I got it. The two operands, both left side and right side, have to be const. 
That is, if I want to overload the operator< as member function, I have to 
define this way:

  bool operator<(Integer const& other) const
  {return this->i < other.i;}


Thanks a lot for help!

Take Care.

Jinming

>From: llewelly@xmission.com
>To: "Jinming Xu" <cybermanxu@hotmail.com>
>CC: gcc-help@gcc.gnu.org
>Subject: Re: C++ template function compilation error
>Date: 20 May 2004 22:48:01 -0600
>
>"Jinming Xu" <cybermanxu@hotmail.com> writes:
>
> > 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;}
> > };
>[snip]
>
>std::sort requires that operator< be able to operate on
>     temporaries. But your operator< takes a reference to
>     non-const. ISO C++ does not allow a temporary to be bound to a
>     reference to non-const. So xlC_r is wrong to accept your code. The
>     solution is to define operator< as taking references to const,
>     like this:
>
>bool operator<(Integer const& lhs, Integer const& rhs)
>   {return lhs.i < rhs.i;}
>

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