Hi,
Using fgets() I can read from stdin and with fputs() I can write to
stdout. Now I have two programs, one writing to stdin and the other
one reading from stdin. And I would like the second program to read
the characters the first program has written to stdin, but I don't get
it how to do this.
The program which writes to stdin:
#include <stdio.h>
int main ()
{
char *string = "Hello\n";
fputs (string, stdin);
return 0;
}
The program which reads from stdin:
#include <stdio.h>
int main ()
{
char buffer [10];
fgets (buffer, 10, stdin);
printf ("%s", buffer);
return 0;
}
Is it possible at all to use such a construction to read from stdin
what an other program wrote to stdin? BTW, I'm using Linux.
Regards,
Harayasu 3 18352
Harayasu wrote: fputs (string, stdin);
^^^^^
Replace that by stdout.
BTW, I'm using Linux.
The stdin/stdout mix-up was your problem. Test the source like this ...
[sven@zeibig stdinout]$ tail out.c
#include <stdio.h>
int main ()
{
char *string = "Hello\n";
fputs (string, stdout);
return 0;
}
[sven@zeibig stdinout]$ tail in.c
#include <stdio.h>
int main ()
{
char buffer [10];
fgets (buffer, 10, stdin);
printf ("%s", buffer);
return 0;
}
[sven@zeibig stdinout]$ gcc -Wall -O3 -pedantic -ansi -o out out.c
[sven@zeibig stdinout]$ gcc -Wall -O3 -pedantic -ansi -o in in.c
[sven@zeibig stdinout]$ ./out | ./in
Hello
[sven@zeibig stdinout]$
HTH
/Sven
--
Sven Semmler http://www.semmlerconsulting.com/
GPG Fingerprint: 72CA E26D C2A3 1FEB 7AFC 10EA F769 A9A4 937F 5E67
Harayasu wrote: Using fgets() I can read from stdin and with fputs() I can write to stdout. Now I have two programs, one writing to stdin and the other one reading from stdin. And I would like the second program to read the characters the first program has written to stdin, but I don't get it how to do this.
The program which writes to stdin:
#include <stdio.h> int main () { char *string = "Hello\n"; fputs (string, stdin);
^^^^^
That should be "stdout"
return 0; }
The program which reads from stdin:
#include <stdio.h> int main () { char buffer [10]; fgets (buffer, 10, stdin); printf ("%s", buffer); return 0; }
Is it possible at all to use such a construction to read from stdin what an other program wrote to stdin? BTW, I'm using Linux.
This is OS dependant, but very common. On Linux, Unix, MSDos, a
Windows command line, you would enter:
writer | reader
and reader will take its stdin from the stdout of writer.
This has nothing to do with the C language, but is elementary OS
usage. This sort of thing is fundamental to writing simple
programs and connecting them via scripts.
--
Chuck F (cb********@yahoo.com) (cb********@worldnet.att.net)
Available for consulting/temporary embedded and systems.
<http://cbfalconer.home.att.net> USE worldnet address!
> Now I have two programs, one writing to stdin and the other one reading from stdin. And I would like the second program to read the characters the first program has written to stdin, but I don't get it how to do this.
One thing that you've probably misinterpreted is that stdin/stdout are
relative to processes. I.e., you should talk about "its" stdin and
"its" stdout when talking about a process. You can think of
stdin/stdout as a couple of connectors to the outer world given to any
running process in your system. stdin can *only* be used to input, and
stdout can *only* be used to output.
So your question (to which you find answers in other posters' replies)
should really be: how do I connect the first program's stdout to the
second program's stdin (so that what the first program outputs to its
stdout is input by the second programs from its stdin).
HTH
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