question about input output redirection in c

haydari · 04-14-2007, 08:08 PM

Hi,

I can redirect the output with a code like this:

#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>

main()
{
int i;
FILE *fid;
fid=open("foo.txt",O_WRONLY | O_CREAT);
close(1);
dup(fid);
close(fid);
for (i =0; i<100;i++)
{
printf("i=%d (%d)\n",i,getpid());
}
}

but when it comes to redirecting input, I can't do this.

fid=open("foo.txt",O_WRONLY | O_CREAT);
close(0);
dup(fid);
close(fid);

doesn't just work. Do you have any idea why and how? :=)

wjevans_7d1@yahoo.co · 04-14-2007, 09:21 PM

When you say "doesn't work", you mean you can't input from fd 0 after that?

You opened it O_WRONLY|O_CREAT, right? You can't input from something opened thus. Is this what you intended?

haydari · 04-15-2007, 09:51 AM

sorry, I did with O_RDONLY and it is ok now.

But I have a new problem.

I can send data to child process with write(fd[1], char_array, strlen(char_array);

I will use it in the child process to redirect the input stream to char_array.

BUT I need to redirect the input to a file not an array.

fid=fid2=open("yarrak.txt",O_RDONLY);
write(fd[1], fid2, 100); 100 is assuming in the file there at most 100 chars. But this doesn't work???

wjevans_7d1@yahoo.co · 04-16-2007, 07:52 AM

I'm not sure I understand the problem.

Read into an array. Write from the array to the output file.

Put that in a loop, and exit the loop when there is nothing more to read.

What am I missing?