[Last Call] Learn about multicloud storage options and how to improve your company's cloud strategy. Register Now

x
?
Solved

To IOStream gurus

Posted on 2001-09-13
13
Medium Priority
?
541 Views
Last Modified: 2013-12-14
Hi,
I am trying to implement logging system using iostreams. My question is: how can I add date/time stamp on iostream basis? What I want to acheive is as following:

cmylog << "Test" << std::endl;

And the output shall be

10:00 Test

(I will be able to configure time stamp format but it is beyond my question, do not worry about it)

Please advise

P.S. I will increase points for working solution.
0
Comment
Question by:proskig
[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
  • 5
  • 4
  • 4
13 Comments
 
LVL 8

Expert Comment

by:mnashadka
ID: 6479119
One way would be to store the data in a std::ostringstream, and when the stream insertion operator is called, you can see if the inserted data is the first data in the ostringstream (by checking ostringstream.str().empty()).  Then, when you see std::endl come in, dump the ostringstream.str() to the file and clear it.  This is the approach I took when I had a similar requirement.  Hope this helps.
0
 
LVL 5

Author Comment

by:proskig
ID: 6479138
mnashadka: What's the correct way to recognize std::endl? I mean flushing buffer? Another question is: which operator to overload ?
0
 
LVL 8

Expert Comment

by:mnashadka
ID: 6479203
Actually, probably an easier way would be to just have 2 stream insertion operators, like:
template<class T>
cmylog &operator<<(T &value)
{
  stream << value;
}

And then another one to dump the ostringstream to the file

cmylog &operator<<(std::ostream &(*end_of_line) (std::ostream &))
{
  file << time() << stream.str() << end_of_line;
  // Clear the ostringstream
}

Of course, the stream variable is the ostringstream and file is the ofstream.
0
Technology Partners: We Want Your Opinion!

We value your feedback.

Take our survey and automatically be enter to win anyone of the following:
Yeti Cooler, Amazon eGift Card, and Movie eGift Card!

 
LVL 7

Expert Comment

by:peterchen092700
ID: 6479213
I once did something similar, providing my own class with this (pseudo-)code:


class mystream
{
  ostream * os;
}

// default template to "redirect" all output to the ostream
template <class T>
mystream & operator << (mystream & s, T const & x)
{
  s->os << x;
}

// specific overload for endl:
mystream & operator << (mystream & s, std::endl const & x)
{
  s->os << x;
  s->os << ... // output time for new line
}

Peter


Note 1: I found the streams extremely slow for this purpose. Since we had to log *tons* of data, I finally rewrote the thing to use printf-style (which is less fun, but more readable and faster)

Note 2: I'm not quite sure about the const & - just tell me if there are problems.

0
 
LVL 8

Expert Comment

by:mnashadka
ID: 6479262
perterchen, what happens if you don't have a new line for a long time?  This is assuming that the next log statement will be coming within seconds.  Just curious.
0
 
LVL 5

Author Comment

by:proskig
ID: 6479604
I do have problems with specialization for std::endl

class mystream
{
  std::ostream *os;
};

// default template to "redirect" all output to the ostream
template <class T>
mystream & operator << (mystream & s, T const & x)
{
 *(s.os) << x;
}

// specific overload for endl:
mystream & operator << (mystream & s, std::endl & x)
{
 *(s.os) << x;
}


Produces error
error C2321: syntax error : unexpected 'endl'

for MSVC
0
 
LVL 7

Expert Comment

by:peterchen092700
ID: 6480172
mnashadka: you're right - in this case, you need to use a flag

class mystream
{
 ostream * os;
 bool needWriteTime; // init to true in CTor
}

// default template to "redirect" all output to the ostream
template <class T>
mystream & operator << (mystream & s, T const & x)
{
 if (s->needWriteTime)
   s->os << "10:00 "; // ;)
 s->os << x;
}

// specific overload for endl:
mystream & operator << (mystream & s, std::endl const & x)
{
 s->os << x;
 s->needWriteTime = true;
}

proksig: I'll look into it, I'm myself not sure with the syntax...
0
 
LVL 8

Expert Comment

by:mnashadka
ID: 6480222
cmylog &cmylog::operator<<(std::ostream &(*end_of_line) (std::ostream &))
is the syntax for endl
0
 
LVL 8

Expert Comment

by:mnashadka
ID: 6480238
I still think it's better to buffer the output, though.  If you don't and your application is (or becomes) multithreaded, your log messages will be interspersed and you won't be able to tell them apart (I know this from experience).  But that's just my 2 cents.
0
 
LVL 7

Expert Comment

by:peterchen092700
ID: 6480300
Hmmm... found a solution, but... seee below..

typedef ostream & (tEndl)(ostream & os);

mystream & operator << (mystream & s,  tEndl x)
{
   tEndl * endlfunc = endl;
   x(*s.os); // s.os << endl;
   if ( x == endlfunc)   // ***
      (*s.os) << "10:40 ";
   return s;
}


I initially thought the endl manip is declared as class - but no, its a function.

The point I find a bit awkward in an STL environment is that at ***, we actually have to compare two function pointers to see if the manipulator passed is actually "endl", or something else (like flush). Although I see no *technical* problem with this.

P.S. next comment: working sample (console app)
0
 
LVL 7

Accepted Solution

by:
peterchen092700 earned 800 total points
ID: 6480303
#include "stdafx.h"
#include <ios>
#include <iostream>

using namespace std;

class mystream
{
   public:
      ostream * os;
      bool      needtime;
      mystream() { needtime = true; }
};

static int time; // instead of time....

// default template to "redirect" all output to the ostream
template <class T>
mystream & operator << (mystream & s, T const & x)
{
   if (s.needtime) {
      ++time;
      (*s.os) << time << " ";  
      s.needtime = false;
   }
 (*s.os) << x;
 return s;
}

int f(int);
int f(int,int);


// specific overload for endl:
//typedef std::basic_ostream<char,std::char_traits<char> >  & (tEndl)(std::basic_ostream<char, std::char_traits<char> > & os);
typedef ostream & (tEndl)(ostream & os);

mystream & operator << (mystream & s,  tEndl x)
{
   x(*s.os); // s.os << x;

   tEndl * endlfunc = endl/*<char, std::char_traits<char> >*/;
   if ( x == endl)
      s.needtime = true;


   return s;
}

int main(int argc, char* argv[])
{
   mystream s;
   s.os = &cout;

   s <<  "Hello World " << endl;
   s <<  "Yeah yeah yeah " << flush << "It works " << endl;    // flush: to test another manip
     return 0;
}

// it's not a clean example... but shows the principles
0
 
LVL 5

Author Comment

by:proskig
ID: 6480420
Cool Thanks!
0
 
LVL 5

Author Comment

by:proskig
ID: 6480431
Cool thanks.
0

Featured Post

Concerto Cloud for Software Providers & ISVs

Can Concerto Cloud Services help you focus on evolving your application offerings, while delivering the best cloud experience to your customers? From DevOps to revenue models and customer support, the answer is yes!

Learn how Concerto can help you.

Question has a verified solution.

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

Update (December 2011): Since this article was published, the things have changed for good for Android native developers. The Sequoyah Project (http://www.eclipse.org/sequoyah/) automates most of the tasks discussed in this article. You can even fin…
Container Orchestration platforms empower organizations to scale their apps at an exceptional rate. This is the reason numerous innovation-driven companies are moving apps to an appropriated datacenter wide platform that empowers them to scale at a …
The viewer will learn how to use and create new code templates in NetBeans IDE 8.0 for Windows.
The viewer will be introduced to the member functions push_back and pop_back of the vector class. The video will teach the difference between the two as well as how to use each one along with its functionality.

650 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