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From: heintze.fmcsse.enet.dec.com (Sieg Heintze)
Newsgroups: comp.lang.c++
Subject: How many arguments for operator() and operator[]?
Summary: How many arguments can operator() and operator[] take?
Keywords: overloading, operator, arguments
Message-ID: <19587@shlump.nac.dec.com>
Date: 30 Jan 91 02:15:33 GMT
Sender: newsdaemon@shlump.nac.dec.com
Organization: Digital Equipment Corporation
Lines: 114

Could someone point me to the place in the Stroustrup and Ellis C++ Reference
manual where they define the number of arguments permitted when defining
a member function that overloads operator() or operator[].

I have tried this program on three compilers and all three behave differently.
I'm wondering how other C++ compilers behave and just what the correct
behavour is.

(1)  ZORTECH only allows 0 or 1 argument for overloading operator ().
(2)  GNU C++ allows two arguments for overloading operator() but not
     operator[].
(3)  TURBO C++ allows two arguments for operator() and operator[].  I assume
     that because it allows two, it will allow larger numbers of arguments 
     also.

I'm told the point is that overloaded operators (including []) look the same as
the builtin versions, so there aren't any differences permitted.  (Check '5.2.1
for the definition of E1[E2] as *((E1)+(E2)) you will not see more than 1
argument.)

Ok, what about operator()?

                                   Thanks,

                                   Sieg

// Experiment with multidimensioned arrays
//

#ifdef __TURBOC__
#include <iostream.h>
#elif defined(__ZTC__)
#include <stream.hpp>
#elif defined (__GNUC__)
#include <stream.h>
#endif

class array
 {
   private:
    float* contents;
    int hi0;
    int hi1;
    int lo1;
    int lo0;
    int m0;
    int m1;
   public:
    array(int low0, int hig0, int low1, int hig1)
     {
      hi0 = hig0; lo0 = low0; hi1 = hig1; lo1 = low1;
      m0 = hi0-lo0+1; m1 = hi1-lo0+1;
      contents = new float[m0 * m1];
     }
    float& operator()()
     {
       return contents[0];
     }
    float& operator()(int row)
     {
      if ((row >= lo1) && (row <= hi1))	return contents[m0*(row-lo1)];
      cout << "Index range error";
      return contents[0];
     }
    float& operator[](int row)
     {
      if ((row >= lo1) && (row <= hi1))	return contents[m0*(row-lo1)];
      cout << "Index range error";
      return contents[0];
     }
// Zortech Compiler won't swallow 3 operands on an operator
    float& operator()(int row, int col)
     {
      if ((row >= lo1) && (row <= hi1)
	 && (col >= lo0) && (col <= hi0))
	 return contents[m0*(row)+col];
      cout << "Index range error";
      return contents[0];
     }
// Neither ZTC or GNUC will swallow this
#ifndef __GNUC__
    float& operator[](int row, int col)
     {
      if ((row >= lo1) && (row <= hi1)
	 && (col >= lo0) && (col <= hi0))
	 return contents[m0*(row)+col];
      cout << "Index range error";
      return contents[0];
     }
#endif
 };
int main()
 {
  array a(1,10, 1, 12);
  cout << " begin main program ";
  a() = 3.14159;
  a(1) = 44.2232;
  a(4,5) = 323.232;
#ifdef __GNUC__
  cout << a() << "   " << a(1) << " " << a(4,5) << '\n';
#else
  a[4,3] = 423.33;
  cout << a() << "   " << a(1) << " " << a(4,5) <<"  "<< a[4,3] << '\n';
#endif
  return 0;
 }



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