Solved

Operator 0verloading

Posted on 2003-12-08
3
268 Views
Last Modified: 2008-03-06
Having a thick morning today - its a monday!

Can you overload operators for enumerations eg:

enum enum1{ enum_list.....};
enum enum2{enum2_lsit.....};

bool operator<(enum1 lhs, enum2 rhs);

Or can you only overload where one of the operands is a class?
0
Comment
Question by:mattjsimps
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
3 Comments
 
LVL 44

Assisted Solution

by:Karl Heinz Kremer
Karl Heinz Kremer earned 50 total points
ID: 9895884
You can overload operators for enums. One example is listed in "The C++ Programming Language" (3rd edition) in 11.2.3 Operators and User-Defined Types.

Your example however would not work: You are comaring two different user defined types (enum1 and enum2). What you can do is:
bool operator<(enum1 lsh, enum1 rhs);

The compiler would not know how to convert your enum2 to an enum1 (or vice versa), so a comparison would not be possible. It's pretty much like comparing apples and oranges :-)

0
 
LVL 11

Accepted Solution

by:
bcladd earned 80 total points
ID: 9896068
khkremer-

You can overload operators for DIFFERENT enums, too. The syntax is exactly as in the post above (see sample program below). The semantics, the meaning of comparing different enums, that is up to the programmer to provide. In the sample code below the macintosh apple is the king of fruit, less than no form of orange. The valencia orang is the trash of fruit, better than no apple. Then the others are compared by their underlying representations. _I_ gave the two this meaning and it is comparing apples and oranges.

mattjsimps-

For programmer convenience if you provide comparisons such as operator<(apple, orange) you should, symetrically, provide operator<(orange, apple).

Sample program:
#include <iostream>

using namespace std;

enum apples { macintosh, delicious, spy, ida_red, NUMBEROFAPPLES };
enum oranges { navel, blood, valencia, NUMBEROFORANGES };

string appleName[] = { "macintosh", "delicious", "spy", "ida_red", "" };
string orangeName[] = { "navel", "blood", "valencia", "" };

bool operator< ( const apples a, const oranges b)
{
  if (a == macintosh) return false;
  if (b == valencia) return true;
  return (int)a > int(b);
}

int main(int argc, char **argv)
{
  for(apples a = macintosh; a <= ida_red; ++a) {
    for (oranges o = navel; o <= valencia; ++o) {
      if (a < o)
        cout << appleName[a] << " < " << orangeName[o] << endl;
      else
        cout << appleName[a] << " NOT < " << orangeName[o] << endl;
    }
  }
 
} /** End of main **/
0
 
LVL 1

Author Comment

by:mattjsimps
ID: 9896348
well spotted. I do in fact want to compare two values of the same type. Told you it was a thick morning!

I am going to increase points to 130 and split 80:50 in bcladd's favour, since the answer answered what i asked.
0

Featured Post

Free Tool: Postgres Monitoring System

A PHP and Perl based system to collect and display usage statistics from PostgreSQL databases.

One of a set of tools we are providing to everyone as a way of saying thank you for being a part of the community.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

When writing generic code, using template meta-programming techniques, it is sometimes useful to know if a type is convertible to another type. A good example of when this might be is if you are writing diagnostic instrumentation for code to generat…
Introduction This article is the first in a series of articles about the C/C++ Visual Studio Express debugger.  It provides a quick start guide in using the debugger. Part 2 focuses on additional topics in breakpoints.  Lastly, Part 3 focuses on th…
The goal of the video will be to teach the user the difference and consequence of passing data by value vs passing data by reference in C++. An example of passing data by value as well as an example of passing data by reference will be be given. Bot…
The viewer will learn additional member functions of the vector class. Specifically, the capacity and swap member functions will be introduced.

726 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question