NetNews Offline 2/NetNews Offline Volume 2.iso/news/comp/lang/c++-part2/13626

Text File | 1996-08-05 | 2.4 KB | 83 lines

Newsgroups: comp.lang.c++
Path: in2.uu.net!shore!mv!usenet
From: [e-mail] (Michael Furman)
Subject: Re: Advanced C++ question...
Message-ID: <[e-mail]>
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Organization: GSSI
Date: Tue, 26 Mar 1996 18:12:50 GMT
References: <4iprfg$1ui@aadt> <[e-mail]> <4j0u62$[e-mail]>
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In article <4j0u62$[e-mail]>, [e-mail] says...
>
>In article <[e-mail]>, [e-mail] (Michael Furman) says:
>>
>>In article <4iprfg$1ui@aadt>, [e-mail] says...
>>>
>>>Hi all...
>>>
>>>I want to write an operator* for a class, but I want to do
>>>one of 2 things:
>>>   1. Call one of two different operator*'s depending on whether
>>>      it is an lvalue or rvalue
>>>   OR
>>>   2. Somehow determine in the function if it is being used as an
>>>      lvalue or an rvalue.
>>>   [......]
>>>The reason for this is that this class accesses data differently
>>depending
>>>on if it is a read or write access.
>>
>>It is impossible with "*" operator. But you can define conversion
>>functions
>>for your class - it will allow exactly what you need.
>>
>
>Could you explain this a bit further.  I have a similar problem to solve.

You can define a special class for using instead if embedded type (pseude_int
instead of int in my example below). Define conversion to value (int) for
reading it and "operator =" for writing:


#include <stdio.h>

class pseudo_int
  {
public:
  operator int()
    {
    printf("Value was read\n");
    return 0;        // Or get / calculate any value and return it
    }
  int operator = (const int & x)
    {
    printf("Value was assigned: %d\n", x);
    // Do whatever you need with value x
    return x;
    }
  // Additional members / member functions if needed
  } xxx;

int main()
  {
  int i;
  i = xxx;
  xxx = 5;
  return 0;
  }


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Michael Furman,                       [phone]
Geophysical Survey Systems, Inc.  fax:[phone]
13 Klein Drive - P.O. Box 97          [e-mail]
North Salem, NH 03073-0097            [e-mail]
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