Custom C++ cout class - output to both console and log file

Question

I'm working on a program that makes heavy use of "cout << strSomething;" to log information to the console. I need to modify the program so that all console output goes to both the console AND a file. Although I can modify the "cout <<" in our code, there are several large third party libraries that also use "cout <<"; those libraries cannot be modified due to their licenses - so modifying all references to "cout <<" is not a solution. Also, the use of "wtee.exe" isn't possible due to the manner in which the command lines are executed.

I am using Visual Studio 2008. I've seen the posting at Google Groups: redirect cout to file, which appears to do EXACTLY what I want to do. The only problem is that the code won't compile. I get C2248 errors "cannot access protected member" on the ->overflow() and ->sync() method calls.

Would anyone know how to get this code to compile? Or an alternate way of redirecting cout to both console and file simultaneously?

Pridgen

Duplicate, I think: https://mcmap.net/q/549315/-how-can-i-compose-output-streams-so-output-goes-multiple-places-at-once – Lowery

(That contains both a Boost and non-Boost solution.) – Lowery

Clever and simple solution here: https://mcmap.net/q/582927/-using-freopen-to-print-to-file-and-screen – Basinet

Answer 1

The sync calls can be replaced with pubsync. As for the overflow call I think that may be a typo. as it looks as if it should be a call to sputc.

Patronizing

Changing "sync" to "pubsync" compiles. But changing to "overflow" to "putc" fails. Error C2039 'putc' is not a member of std::basic_streambuf<_Elem,_Traits> – Pridgen

Sorry, that was a typo. in my answer. I corrected it to sputc. – Patronizing

In our situation (unable to use Boost, unable to modify 3rd party libraries), this was the best solution. – Pridgen

Answer 2

The boost::iostreams::tee_device is made for this

#include <boost/iostreams/stream.hpp>
#include <boost/iostreams/tee.hpp>

#include <fstream>
#include <iostream>

int
main()
{
    typedef boost::iostreams::tee_device<std::ostream, std::ofstream> Tee;
    typedef boost::iostreams::stream<Tee> TeeStream;

    std::ofstream file( "foo.out" );
    Tee tee( std::cout, file );

    TeeStream both( tee );

    both << "this goes to both std::cout and foo.out" << std::endl;

    return 0;
}

sample invocation:

samm$ ./a.out
this goes to both std::cout and foo.out
samm$ cat foo.out
this goes to both std::cout and foo.out
samm$ 

Giarla

This works just fine for me - unfortunately, I've been asked to NOT include Boost as part of this application. Management, non-technical based decision. So - how do you do this in just std? – Pridgen

@Jason it looks like there are some other answers that do not use boost. Good luck. – Giarla

Answer 3

This easily extends to additional streams.

OstreamFork.hpp -- Distribute data to 2 streams simultaneously

#include <iomanip>
#include <fstream>
#include <iostream>
using namespace std ;

class ostreamFork           // Write same data to two ostreams
{
public:
  ostream& os1 ;
  ostream& os2 ;

  ostreamFork( ostream& os_one , ostream& os_two )
  : os1( os_one ) ,
    os2( os_two )
  {}

 } ;

                          // For data: int, long , ...
 template <class Data>
 ostreamFork& operator<<( ostreamFork& osf , Data d )
 {
   osf.os1 << d ; 
   osf.os2 << d ;
   return osf ;
 }
                        // For manipulators: endl, flush
 ostreamFork& operator<<( ostreamFork& osf , ostream& (*f)(ostream&)  )
 {
   osf.os1 << f ; 
   osf.os2 << f ;
   return osf ;
 }

                            // For setw() , ...
template<class ManipData>
 ostreamFork& operator<<( ostreamFork& osf , ostream& (*f)(ostream&, ManipData )  )
 {
   osf.os1 << f ; 
   osf.os2 << f ;
   return osf ;
 }

TestOstreamFork.cpp:

#include "stdafx.h"
#include <fstream>
  using namespace std ;
#include "ostreamFork.hpp"

int main(int argc, char* argv[])
{
  ofstream file( "test2.txt" ) ;
  ostreamFork osf( file , cout ) ;

  for ( int i = 0 ; i < 10 ; i++ )
  {
    osf << i << setw(10) << " " << 10*i << endl  ;
  }

    return 0 ;
}

Output to both cout and test2.txt:

0          0
1          10
2          20
3          30
4          40
5          50
6          60
7          70
8          80
9          90

Sully

Answer 4

if you're desperate:

#define protected public
#include <iostream>
#undef protected

this is a gross hack, but it usually works.

Groenendael

At this point, I'm desperate enough to take even an ugly hack. Unfortunately, with VS2008, it doesn't help. Same original errors. – Pridgen

Answer 5

What you can do is capture the std::cout.rdbuf() with a pointer to std::streambuf, then i think you should be able to write all the outputs to std::cout to some file.

Farias

Answer 6

you can just use a wrapper class to do so, somthing like this

#include <iostream>
#include <fstream>

...

class streamoutput
{
    std::ofstream fileoutput;
    public:
    streamoutput(char*filename){
        fileoutput.open(filename);
    }
    ~streamoutput(){
        fileoutput.close();
    }
    template<class TOut> streamoutput& operator <<(const TOut& data)
    {
        fileoutput << data;
        std::cout << data;
        return this;
    }
};

extern streamoutput cout("logfile.log");

declare cout like that and just change all your #include <iostream> to include this wrapper (remeber cout is external variable so you have to declere it in one of your source codes too).

Falsework

This will work for the code that we write, were we can modify our #include <iostream> lines. But this won't work for the third-party code, that must also be using #include <iostream>, but we can't modify due to licensing. – Pridgen

then you can just modify iostream file instead! no lisence can prevent you from that! but if you have a precompiled code that's totaly a diffrent story, but you can also write a wrapper program that runs yours and do all the console works for you. though it'll take somehow much more effort! – Falsework

Answer 7

Sorry to warm this up so late, but this here should be a solution with redirection of cout to a teebuffer based on Dietmar Kühl's solution on Google groups.

Usage is simply

GetSetLog log("myfile.log");

During the lifetime of the object "log" everything will be written to both cout/cerr and file

https://sourceforge.net/p/getset/code/ci/master/tree/GetSet/GetSetLog.hxx

Reciprocity