Stream Redirection. Newbies question

[Alexander Baranov]

Hi.
I work in Debian Linux GCC. I have a function, which opens a socket and
binds 'mystream' stream with this socket (by fdopen command). Then, while
being inside this function I want stdout be redirected to mystream. On
exiting the function I have to return stdout to ordinary stdout.
I did it like this:

Entering function
{
...
FILE* sos_stdout;
sos_stdout = stdout; //reserving stdout
stdout = mystream; //redirecting
....
doing something
....
stdout = sos_stdout; //returning stdout back
fclose(mystream); //closing my stream
.....
Exiting..
}

It works, but I still have a feeling that I do it in a wrong way. Please,
advise if it is really so.
Regards, Alex.

 

[Kenneth Brody]

Alexander Baranov wrote:
[...]

FILE* sos_stdout;
sos_stdout = stdout; //reserving stdout
stdout = mystream; //redirecting

This statement won't work on all platforms, as "stdout" may not be an
lvalue. For example, several of my systems have stdio.h lines like:

#define stdin (&__iob[0])
#define stdout (&__iob[1])
#define stderr (&__iob[2])

[...]

--
+-------------------------+--------------------+-----------------------------+
| Kenneth J. Brody | www.hvcomputer.com | |
| kenbrody/at\spamcop.net | www.fptech.com | #include <std_disclaimer.h> |
+-------------------------+--------------------+-----------------------------+
Don't e-mail me at: <[email protected]>

 

[Dan Pop]

Entering function
{
..
FILE* sos_stdout;
sos_stdout = stdout; //reserving stdout
stdout = mystream; //redirecting
...
doing something
...
stdout = sos_stdout; //returning stdout back
fclose(mystream); //closing my stream
....
Exiting..
}

It works, but I still have a feeling that I do it in a wrong way. Please,
advise if it is really so.

You're right. stdin, stdout and stderr need not be modifiable lvalues,
so you may not be allowed to assign anything to them (even if it works
on your particular implementation).

Use fprintf on mystream instead of printf (ditto for fputs instead puts)
and you don't have to mess with stdout.

Dan