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Can I redirect stdout to a file AND the console.

 
 
Jef Driesen
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      11-23-2007
I wrote a program that writes a large amount of information to stdout
(and stderr). When run from the commandline, this output either appears
on the console window (the default) or can be redirected to a file by
means of the freopen() function:

freopen ("logfile.txt", "w", stdout);

But I would like to have the output on the console AND a logfile. Is
this possible (without using an extra program like 'tee')?
 
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Richard Bos
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      11-23-2007
Jef Driesen <(E-Mail Removed)> wrote:

> I wrote a program that writes a large amount of information to stdout
> (and stderr). When run from the commandline, this output either appears
> on the console window (the default) or can be redirected to a file by
> means of the freopen() function:
>
> freopen ("logfile.txt", "w", stdout);
>
> But I would like to have the output on the console AND a logfile. Is
> this possible (without using an extra program like 'tee')?


Not without writing it twice.

Richard
 
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santosh
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Posts: n/a
 
      11-23-2007
In article <fi60in$vh9$(E-Mail Removed)>, Jef Driesen
<(E-Mail Removed)> wrote on Friday 23 Nov 2007 1:17 pm:

> I wrote a program that writes a large amount of information to stdout
> (and stderr). When run from the commandline, this output either
> appears on the console window (the default) or can be redirected to a
> file by means of the freopen() function:
>
> freopen ("logfile.txt", "w", stdout);
>
> But I would like to have the output on the console AND a logfile. Is
> this possible (without using an extra program like 'tee')?


Yes. Duplicate your output to both stderr and to the file. You can use a
small "wrapper" function to encapsulate this functionality.

In any case you need to use two different file streams. You can't route
output to multiple devices by writing to the same stream within
Standard C. It might be possible with platform specific functions, but
you need to ask in a group appropriate for your system.

 
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Richard Heathfield
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      11-23-2007
santosh said:

> In article <fi60in$vh9$(E-Mail Removed)>, Jef Driesen
> <(E-Mail Removed)> wrote on Friday 23 Nov 2007 1:17 pm:
>

<snip>
>>
>> But I would like to have the output on the console AND a logfile. Is
>> this possible (without using an extra program like 'tee')?

>
> Yes. Duplicate your output to both stderr and to the file. You can use a
> small "wrapper" function to encapsulate this functionality.


Something like this, perhaps (but see the note that follows):

#include <stdio.h>
#include <stdarg.h>

int tfprintf(FILE *fpa, FILE *fpb, const char *fmt, ...)
{
int rc = 0;
va_list ap = {0};
va_start(ap, fmt);
rc = vfprintf(fpa, fmt, ap);
va_end(ap);
if(rc >= 0)
{
va_start(ap, fmt);
rc = vfprintf(fpb, fmt, ap);
va_end(ap);
}
return rc;
}

This function's handling of the return values from the two vfprintf calls
is not particularly satisfactory, but it's hard to see how one could come
up with a solution that would be pleasing to everyone. Here's one
possibility:

int tfprintf(int *rcb, FILE *fpa, FILE *fpb, const char *fmt, ...)

(with the obvious changes within the function itself), so that the function
returns the value returned by the first vfprintf, and *rcb is populated
with the value returned by the second vfprintf.

Here's another solution:

struct tfprintf_rt_
{
int rca;
int rcb;
};

struct tfprintf_rt_ tfprintf(FILE *fpa, FILE *fpb, const char *fmt, ...)

And here's another:

#define TFPRINTF_BOTH_OK 0
#define TFPRINTF_FAIL1 1
#define TFPRINTF_FAIL2 2
#define TFPRINTF_BOTH_BAD (TFPRINTF_FAIL1 | TFPRINTF_FAIL2)

int tfprintf(struct tfprintf_rt_ *rc, FILE *fpa, FILE *fpb, const char
*fmt, ...)

with the return value giving a quick and dirty summary in bitflag form,
with the details stored in the struct for perusal if required.

But they all suck, really, don't they? It's just a matter of finding the
method that sucks *least*, whether it is one of these or some other
construction - and that's very much a personal style choice.

--
Richard Heathfield <http://www.cpax.org.uk>
Email: -http://www. +rjh@
Google users: <http://www.cpax.org.uk/prg/writings/googly.php>
"Usenet is a strange place" - dmr 29 July 1999
 
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those who know me have no need of my name
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Posts: n/a
 
      11-24-2007
in comp.lang.c i read:

>I wrote a program that writes a large amount of information to stdout
>(and stderr).


>But I would like to have the output on the console AND a logfile. Is
>this possible (without using an extra program like 'tee')?


in addition to leaving it to the person using your program to arrange for
it and the other response(s) (output twice), it may be worth noting that
the semantics of the filename parameter is implementation defined so it may
be possible without any more effort than the formulation of the argument
value. but i wouldn't count on it, and a strictly conforming program
cannot, so perhaps it is best to find another way.

--
a signature
 
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CBFalconer
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      11-24-2007
those who know me have no need of my name wrote:
> Jef Driesen wrote:
>
>> I wrote a program that writes a large amount of information to
>> stdout (and stderr).

>
>> But I would like to have the output on the console AND a logfile.
>> Is this possible (without using an extra program like 'tee')?

>
> in addition to leaving it to the person using your program to
> arrange for it and the other response(s) (output twice), it may
> be worth noting that the semantics of the filename parameter is
> implementation defined so it may be possible without any more
> effort than the formulation of the argument value. but i
> wouldn't count on it, and a strictly conforming program cannot,
> so perhaps it is best to find another way.


Simple. Write the program with a 'putdouble' routine, that writes
a char to both of two separate files. Let the command structure
select those files. You can also arrange to have default names,
which may include stdout and null.

--
Chuck F (cbfalconer at maineline dot net)
<http://cbfalconer.home.att.net>
Try the download section.



--
Posted via a free Usenet account from http://www.teranews.com

 
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Jef Driesen
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Posts: n/a
 
      11-24-2007
those who know me have no need of my name wrote:
> in comp.lang.c i read:
>
>> I wrote a program that writes a large amount of information to stdout
>> (and stderr).

>
>> But I would like to have the output on the console AND a logfile. Is
>> this possible (without using an extra program like 'tee')?

>
> in addition to leaving it to the person using your program to arrange for
> it and the other response(s) (output twice), it may be worth noting that
> the semantics of the filename parameter is implementation defined so it may
> be possible without any more effort than the formulation of the argument
> value. but i wouldn't count on it, and a strictly conforming program
> cannot, so perhaps it is best to find another way.


The problem is that I have an application that needs to be tested by a
number of people and they have to send the results back to me. Therefore
I redirect stdout and stderr to a file that is easy to send. But that
way, nothing appears on the console which gives the impression there is
no progress.

The test persons are not always very skilled computer users, so I want
to make it as easy as possible to run the test. Therefore I want to
avoid to explain how to redirect output them self. Also my testers are
mostly running Windows and they do not have a 'tee' utility.
 
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Jef Driesen
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Posts: n/a
 
      11-24-2007
santosh wrote:
> In article <fi60in$vh9$(E-Mail Removed)>, Jef Driesen
> <(E-Mail Removed)> wrote on Friday 23 Nov 2007 1:17 pm:
>
>> I wrote a program that writes a large amount of information to stdout
>> (and stderr). When run from the commandline, this output either
>> appears on the console window (the default) or can be redirected to a
>> file by means of the freopen() function:
>>
>> freopen ("logfile.txt", "w", stdout);
>>
>> But I would like to have the output on the console AND a logfile. Is
>> this possible (without using an extra program like 'tee')?

>
> Yes. Duplicate your output to both stderr and to the file. You can use a
> small "wrapper" function to encapsulate this functionality.


That requires rewriting my application (and all libraries it depends
on). That is something I wanted to avoid because I need it for testing.

> In any case you need to use two different file streams. You can't route
> output to multiple devices by writing to the same stream within
> Standard C. It might be possible with platform specific functions, but
> you need to ask in a group appropriate for your system.


Do you happen to know if it can be done on Windows? I can't find
anything, but I don't know what function to look after.
 
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Kenny McCormack
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Posts: n/a
 
      11-24-2007
In article <FY_1j.223213$(E-Mail Removed)-ops.be>,
Jef Driesen <(E-Mail Removed)> wrote:
>those who know me have no need of my name wrote:
>> in comp.lang.c i read:
>>
>>> I wrote a program that writes a large amount of information to stdout
>>> (and stderr).

>>
>>> But I would like to have the output on the console AND a logfile. Is
>>> this possible (without using an extra program like 'tee')?

>>
>> in addition to leaving it to the person using your program to arrange for
>> it and the other response(s) (output twice), it may be worth noting that
>> the semantics of the filename parameter is implementation defined so it may
>> be possible without any more effort than the formulation of the argument
>> value. but i wouldn't count on it, and a strictly conforming program
>> cannot, so perhaps it is best to find another way.

>
>The problem is that I have an application that needs to be tested by a
>number of people and they have to send the results back to me. Therefore
>I redirect stdout and stderr to a file that is easy to send. But that
>way, nothing appears on the console which gives the impression there is
>no progress.
>
>The test persons are not always very skilled computer users, so I want
>to make it as easy as possible to run the test. Therefore I want to
>avoid to explain how to redirect output them self. Also my testers are
>mostly running Windows and they do not have a 'tee' utility.


I Expect there is a simple solution to this...

http://bmrc.berkeley.edu/people/chaffee/expectnt.html

It's a little old (and, of course, completely OT [heh heh]), but it
works very well. I've used it for years.

 
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CBFalconer
Guest
Posts: n/a
 
      11-24-2007
Jef Driesen wrote:
>

.... snip ...
>
> The test persons are not always very skilled computer users, so I
> want to make it as easy as possible to run the test. Therefore I
> want to avoid to explain how to redirect output them self. Also my
> testers are mostly running Windows and they do not have a 'tee'
> utility.


So write one. It isn't hard.

--
Chuck F (cbfalconer at maineline dot net)
<http://cbfalconer.home.att.net>
Try the download section.



--
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