Solved

How to correctly derive from ostream class?

Posted on 1998-11-05
5
360 Views
Last Modified: 2008-02-01
I am a novice C++ programmer, and this is very basic.

I would like define a Log class derived from ostream,
so that in it's simple implemenation it would just print
to cout, and in the later version it would write to a file.
I am looking for something like as follows.

#include <ostream.h>

class Log : ostream
{
public:
  ...
  ..

}

main(int argc, char *argv)
{

  log Log;

  log << "Logging data" << endl;

}

Thanks,
daniel
0
Comment
Question by:danchandran
  • 3
  • 2
5 Comments
 
LVL 22

Accepted Solution

by:
nietod earned 50 total points
ID: 1177046
To derive from ostream for your purposes you woul want to use pubic derivation, like

class Log : public ostream
 {
   public:
     ...
     ..

 }

then you would overide any member procedures you would like changed.  Unfortunately, considering what you are proposing there are many such procedures you might need to change.  (all the operator << procedures) for example.   This could be a lot of work.  I suspect there might be a better way to accomplish your goals, except I'm not sure what your goal is.  What exactly are you hoping to achieve?


0
 
LVL 22

Expert Comment

by:nietod
ID: 1177047
One possibility might be a log class that is not derived from a stream, but contains a stream pointer and has a "ostream &" operator that returns the dereferenced stream pointer.  That might work well for your needs.  
0
 

Author Comment

by:danchandran
ID: 1177048

I am looking way of this implementation of the Log Class

class Log :
{
   public:
          Log();
          ~Log();
        Write(int);
        Write(char *);
        Write(float);
        ....

}

I have a whole bunch of overloaded Write methods, and I was hoping that by doing
something like what I have asked, I could get around it.

Thanks,
daniel
0
 
LVL 22

Expert Comment

by:nietod
ID: 1177049
Then my final suggestion should work well for you--I think.

1.  Make the Log class contain a pointer to the stream it should output to.  This pointer should be set by the constructor (and/or default to cout)
2.  Remove the Write() functions.
3.   Add a stream & conversion operator so that the class can be used wherever a stream would be used.  

you should have something like

class Log :
{
   ostream *StmPtr;
public:
   Log(stream *Ptr = &cout) : StmPtr(Ptr) {};
    ~Log();
   SetStmPtr(ostream *Ptr = &cout) { StmPtr = Ptr; };
   operator ostream & () { return *StmPtr; };
 }

this should allow yout to do things like

Log ALog;
ofstream FilStm("C:\\LOG.TXT");

ALog << " output to cout. " << endl;
ALog.SetStmPtr(&FilStm);
ALog << " output to a file. " << endl;

0
 

Author Comment

by:danchandran
ID: 1177050
Thanks,

I have almost a similar implementation working!!

daniel
0

Featured Post

Networking for the Cloud Era

Join Microsoft and Riverbed for a discussion and demonstration of enhancements to SteelConnect:
-One-click orchestration and cloud connectivity in Azure environments
-Tight integration of SD-WAN and WAN optimization capabilities
-Scalability and resiliency equal to a data center

Question has a verified solution.

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

Suggested Solutions

Title # Comments Views Activity
returning a dereferenced pts in C++ 10 158
computer science syllabus 3 88
Add values of each row in an array 3 64
learn programming 8 37
Article by: SunnyDark
This article's goal is to present you with an easy to use XML wrapper for C++ and also present some interesting techniques that you might use with MS C++. The reason I built this class is to ease the pain of using XML files with C++, since there is…
Templates For Beginners Or How To Encourage The Compiler To Work For You Introduction This tutorial is targeted at the reader who is, perhaps, familiar with the basics of C++ but would prefer a little slower introduction to the more ad…
The viewer will learn additional member functions of the vector class. Specifically, the capacity and swap member functions will be introduced.
The viewer will learn how to clear a vector as well as how to detect empty vectors in C++.

856 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