Re: is it possible to make a map of objects?

From:

Richard Herring <junk@[127.0.0.1]>

Newsgroups:

comp.lang.c++

Date:

Fri, 17 Aug 2007 11:44:08 +0100

Message-ID:

<gIxyXWG4vXxGFw$A@baesystems.com>

In message <fa1hod$152h$1@news.vol.cz>, Milan Krejci
<rdw@no-spam.mail.cz> writes

Paul napsal(a):

"Milan Krejci" <rdw@no-spam.mail.cz> wrote in message
news:fa1d8c$121c$1@news.vol.cz...

hello, sorry to bother you with this but i can't seem to figure out
why i can't do:

struct SD {
int from;
int to;
} sd;
std::map<sd,std::string> ListOfWorkingSchedule;

First, "sd" is the name of the variable, not the type:
--------------------------------------------------------------------
#include <map>
#include <string>
struct SD {
int from;
int to;
}sd;
std::map<SD, std::string> ListOfWorkingSchedule;
--------------------------------------------------------------------
After this change, you will still get a compiler error, albeit a
different one. Then once you get this new error, try to understand
what it means. If you can't figure it out, post the compiler error
(I know what the problem is -- I'm seeing if you know what the problem is).
Paul

yes, it complains about missing overloaded < operator. i added one but
don't know if correctly
      bool operator<(SD const &sd1) {
      if (sd1.from<this.from)
              return true;
      }

doba.h:11: error: `from' is not a type
doba.h:11: error: request for member of non-aggregate type before ')' token

Once you've made the obvious correction to fix these errors, consider
this:

If the condition is false, what does the operator return?

If your operator< doesn't define a strict weak ordering (look it up) the
map will not behave as you would expect.

--
Richard Herring