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@xxxxxxxxxxxx To: "Jinming Xu" <cybermanxu@xxxxxxxxxxx> CC: gcc-help@xxxxxxxxxxx Subject: Re: C++ template function compilation error Date: 20 May 2004 22:48:01 -0600
"Jinming Xu" <cybermanxu@xxxxxxxxxxx> 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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