Cannot correctly connect multi-stage C command pipe (among others) (FYI: a lot of code) Post: 302787955

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Homework and Emergencies Homework & Coursework Questions Cannot correctly connect multi-stage C command pipe (among others) (FYI: a lot of code) Post 302787955 by kowit010 on Sunday 31st of March 2013 02:12:59 PM

03-31-2013

Registered User

Re:

Yeah, I know, sorry the code is so huge, I guess I had to post the whole code so the mods don't come down on me for not filling out the whole thread template, but anyway... I wish I had time to simplify the code, now I'm just trying to get this thing going. I changed the code to this (just including the problem area in the "create_command_process" function):

Code:

if(childpid=fork())//if more than one process, and this is the parent process....
 {
  if((cmd_pids[i]=(int)childpid)==-1)//did it fork correctly?
  {
   perror("Error forking!");
   exit(666);
  }
  close(prev[0]);//close previous filedescriptor in
  close(prev[1]);//close previous filedescriptor out
  close(curr[0]);
  close(curr[1]);
 }
 else
 {
  if(prev[1]!=-1)//if previous pipe has a valid item
  {
      dup2(prev[0],0);
      dup2(prev[1],1);
      close(prev[0]);
      close(prev[1]);
  }
  if(curr[0]!=-1)//if current pipe has a valid item
  {
      dup2(curr[0],0);
      dup2(curr[1],1);
      close(curr[0]);
      close(curr[1]);
  }
    execvp(test,argvector);//execute the process....
 }

When I run it with "ls | wc", absolute NO output to the shell console comes back (even though it's writing stuff to my logfile). I will work on this some more, but I don't know if this means it's working now? Aren't I like supposed to get a set of numbers back for "ls | wc"? (running it in shell spits out "16 16 150" in my current folder). Then again, the assignment description says this, and I quote:

"　
The standard output stream is used and used only for printing command execution results.
"

So I take this to mean I shouldn't have to worry enough about it printing anything straight to the console?

---------- Post updated at 01:12 PM ---------- Previous update was at 01:11 PM ----------

Quote:

Originally Posted by Corona688

Also, exit(666) makes no sense. It only takes numbers 1-127.

Oh, really? I didn't know that. I just heard that any non-zero number fed into an exit() call indicated failure so I use 666 to be a wise guy for obvious reasons, bahahaha. I'll change it, though, to be something in that valid range. Thanks.

kowit010

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LEARN ABOUT OPENDARWIN

pipe

PIPE(2) 						      BSD System Calls Manual							   PIPE(2)

NAME

     pipe -- create descriptor pair for interprocess communication

SYNOPSIS

     #include <unistd.h>

     int
     pipe(int *fildes);

DESCRIPTION

     The pipe() function creates a pipe, which is an object allowing unidirectional data flow, and allocates a pair of file descriptors.  The
     first descriptor connects to the read end of the pipe, and the second connects to the write end, so that data written to fildes[1] appears on
     (i.e., can be read from) fildes[0].  This allows the output of one program to be sent to another program: the source's standard output is set
     up to be the write end of the pipe, and the sink's standard input is set up to be the read end of the pipe.  The pipe itself persists until
     all its associated descriptors are closed.

     A pipe whose read or write end has been closed is considered widowed.  Writing on such a pipe causes the writing process to receive a SIGPIPE
     signal.  Widowing a pipe is the only way to deliver end-of-file to a reader: after the reader consumes any buffered data, reading a widowed
     pipe returns a zero count.

RETURN VALUES

     On successful creation of the pipe, zero is returned. Otherwise, a value of -1 is returned and the variable errno set to indicate the error.

ERRORS

     The pipe() call will fail if:

     [EMFILE]		Too many descriptors are active.

     [ENFILE]		The system file table is full.

     [EFAULT]		The fildes buffer is in an invalid area of the process's address space.

SEE ALSO

     sh(1), read(2), write(2), fork(2), socketpair(2)

HISTORY

     A pipe() function call appeared in Version 6 AT&T UNIX.

4th Berkeley Distribution					   June 4, 1993 					 4th Berkeley Distribution