piping/reading stdin quirks.

[chad kline]

FBSD 4.8/GCC

////////
C-CODE:
////////

char c;

while ( 1 ) {

read(0, &c, 1); printf("%02x ", c);
close(0); open("/dev/stdin", O_RDWR, S_IRUSR|S_IWUSR);
}

//////////
Question:
//////////

this is confusing to me. 'open' doesn't reopen 'stdin'
('errno' keeps getting set, and no new characters are
ever read - after the 1st one).

i have a function that opens, reads, and closes a file.
i would like to use this function to read a file piped
from 'stdin' as well as from disk. the problem is i
can't re-open 'stdin' after the file reading function
closes '/dev/stdin'.

is there any way to "reset" /dev/stdin so that
it functions normally after being close(2)'d?

 

[Barry Schwarz]

FBSD 4.8/GCC

////////
C-CODE:
////////

char c;

while ( 1 ) {

read(0, &c, 1); printf("%02x ", c);
close(0); open("/dev/stdin", O_RDWR, S_IRUSR|S_IWUSR);
}

Unfortunately, it is not standard c. Neither open nor close are
defined in the standard library.


<<Remove the del for email>>

 

[chad kline]

FBSD 4.8/GCC

actually, i have a better example of what i am trying to do.
i have searched "everywhere" for the solution, and have seen
the question asked in many places, but without any clear answers.

#include <errno.h>
#include <stdio.h>
#include <unistd.h>
////////////////////////////////////////////////////
int main(int argc, char* argv[]) {

char c, fd2, err;

fd2 = dup(0);
while ((err = read(0, &c, 1))) { // read pipe.
printf("R: %i:%i:%02x\n", errno, err, c);
} errno=0;
err = dup2(fd2, 0);
printf("2: %i:%i:%02x\n", errno, err, c);
errno=0;
while ((err = read(0, &c, 1))) { // read keyb.
printf("R: %i:%i:%02x\n", errno, err, c);
}

exit(0);}
////////////////////////////////////////////////////

this doesn't work - what needs to be done to make it work?
if i avoid all 'dup's and just continue to read stdin after
reading the pipe, the 2nd read just keeps reading the last
char of the piped file (generating errno's).

i want to make stdin read the keyboard after reading the pipe.
i don't want to use 'streams' (fopen, freopen, etc).

 

[Jack Klein]

actually, i have a better example of what i am trying to do.
i have searched "everywhere" for the solution, and have seen
the question asked in many places, but without any clear answers.

#include <errno.h>
#include <stdio.h>
#include <unistd.h>

^^^^^^^^^^^^^^^^^^^^^

Stop right there, this header is NOT part of C. The minute you
include it, you're off-topic here. Ask in a group that supports your
particular compiler/OS combination.

--
Jack Klein
Home: http://JK-Technology.Com
FAQs for
comp.lang.c http://www.eskimo.com/~scs/C-faq/top.html
comp.lang.c++ http://www.parashift.com/c++-faq-lite/
alt.comp.lang.learn.c-c++ ftp://snurse-l.org/pub/acllc-c++/faq

 

[chad kline]

FBSD 4.8/GCC

this defines much better the problem
i am trying to solve. it would be
better if the '/dev/tty' stuff
wasn't necessary.

#include <errno.h>
#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>
/////////////////////////////////////////
int main(int argc, char* argv[]) {

char c; int n, fd;

while ((n = read(0, &c, 1))) // read pipe.
printf("PIPE: %02x:%i\n", c, n);

fd=open("/dev/tty", O_RDWR, 0600);
printf("OPEN: %i:%i\n", errno, fd);

dup2(fd,0); close(fd);

while ((n = read(0, &c, 1)) < 1 ); // wait keyb.
printf("KEYB: %02x:%i\n", c, n);

exit(0);}
/////////////////////////////////////////

 

[chad kline]

FBSD 4.8/GCC

i apologize for the several posts,
but since it takes 10 hours or so
to post, i was able to figure some
things out, and think it's good
knowledge to have in the DB. it
seems to be a question without
many good answers (not that the
one i found is "good", not sure).

#include <errno.h>
#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>
///////////////////////////////////////////////////
int main(int argc, char* argv[]) {

char c; int n;

while ((n = read(0, &c, 1))) // read pipe.
printf("PIPE: %02x:%i\n", c, n);

dup2(1,0);

while ((n = read(0, &c, 1)) < 1 ); // wait keyb.
printf("KEYB: %02x:%i\n", c, n);

exit(0);}
///////////////////////////////////////////////////

 

[Irrwahn Grausewitz]

i apologize for the several posts,
but since it takes 10 hours or so
to post, i was able to figure some
things out, and think it's good
knowledge to have in the DB. it
seems to be a question without
many good answers (not that the
one i found is "good", not sure).

#include <errno.h>
#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>

But still it's hopelessly off-topic in comp.lang.c, as you are dealing
with non-standard extensions to the C language.

To echo Jack Klein:
Ask in a group that supports your particular compiler/OS combination.

<SNIP>

Regards