Re: operator < stopped working

"Victor Bazarov" <>
Tue, 2 Oct 2007 15:02:36 -0400
raan wrote:

All were working well until I decided to add a copy constructor.
Please see the program. I am getting

"c:\Program Files\Microsoft Visual Studio .NET 2003\Vc7\include
\functional(139) : error C2679: binary '<' : no operator found which
takes a right-hand operand of type 'const D' (or there is no
acceptable conversion)

Seems like I can't guarantee constant-ness anymore with the copy
constructor. How do I get around with this ?

// test-sets.cpp : Defines the entry point for the console

#include "stdafx.h"
#include <iostream>
#include <set>
#include <map>

using namespace std;

class D

  string a;


Please drop the semicolons after the function bodies. They are
so ugly.

  //Copy constructor
  D(D& d)

The usual signature (the compiler-generated one's at least) is

   D(D const& d)

  std::string& getA()
    return a;

There is also a need to have a const version of that function:

    std::string const& getA() const
        return a;

Don't let it throw you off that they have the same body, they are

  bool operator < (D d) const

The usual (idiomatic) way is to pass the operand by a reference
to cons:

    bool operator < (D const& d) const

    if( <0){
      return true;
    }else {
      return false;

int main()
   typedef std::set<D> dsets;


   D *d = new D();


   dsets s;


 return 0;

What you should write is

    std::set<D> dsets;

Or at least

    std::set<D> dsets;
    D d;

Drop the habit of doing "new" all the time. Besides, you're
inconsistent. You didn't 'new' your 'dsets' object!

Please remove capital 'A's when replying by e-mail
I do not respond to top-posted replies, please don't ask

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