Implementing 2 pipes between a parent and child process Post: 84432

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Top Forums Programming Implementing 2 pipes between a parent and child process Post 84432 by bwgoudey on Saturday 24th of September 2005 10:07:38 PM

09-24-2005

Registered User

Implementing 2 pipes between a parent and child process

Hi all,
I'm trying to write a program that has some data it wants to send through a filter program(in this case tr), and then recieve the output from that filter program. The way I'm trying to do it is by setting up two pipes between the programs and piping the data in through one pipe and back out through the other one. However all it does at the minute is hang. I think waiting for input from stdin but I can't figure out why. I'm guessing that the child process must not be getting sent any data but I don't how know how to fix it.

Here is the code (sorry if its a little long)

Code:

int main (void)
{
    pid_t pid;
    int pipe_in[2];
    int pipe_out[2];
    char buffer[800];

    /* Create the pipe.  */
    pipe (pipe_in);
    pipe (pipe_out);

    /* Create the child process.  */
    pid = vfork ();
    if (pid == (pid_t) 0) /* child 1 */
    {
		/*close unneeded*/
                close(pipe_in[1]);
                close(pipe_out[0]);
		
		/*Make pipes the stdin and stdout*/
                dup2(pipe_in[0], 0);
                close(pipe_in[0]);
                dup2(pipe_out[1], 1);
                close(pipe_out[1]);

		/*change a to b*/ 
                execl("/bin/tr", "tr", "a", "b" , 0);
                perror("exec prog1");
                exit(1);
    }
    else /*parent*/
    {
                /*close unneeded*/
                close(pipe_in[0]);
                close(pipe_out[1]);
                /*write to and then read from child*/
                write(pipe_in[1], "This is the data\n", 14);
                read(pipe_out[0], buffer, sizeof(buffer));

                /*send EOF to child*/
                close(pipe_in[1]);
                /*wait for end then close other end of pipe*/
                waitpid(pid, NULL, 0);
                close(pipe_out[0]);
                return EXIT_SUCCESS;
    }
}

Any help is greatly appreciated
Ben Goudey

bwgoudey

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LEARN ABOUT HPUX

smfi_register

smfi_register(3N)														 smfi_register(3N)

NAME

       smfi_register() - registers a set of filter callbacks for sendmail

SYNOPSIS

PAMAMETERS

       descr	 Specifies a filter descriptor of type describing the filter's functions.

DESCRIPTION

       The  creates a filter using the information given in the smfiDesc argument.  must be called before the routine.	Multiple calls to the rou-
       tine within a single process is not allowed.

       The structure has the following members:

       A NULL value for any callback function indicates that the filter does not wish to process the given type  of  information  and  the  filter
       returns the value.

   Notes
       The flags field must contain the bitwise OR of 0 (zero) or more of the following values:

       This filter adds headers.

       This filter changes and deletes headers.

       This filter replaces the body of the message during the filtering process.
			   may have significant performance impact if other filters do body filtering after

       This filter adds recipients to the message.

       This filter removes recipients from the
			   message.

RETURN VALUE

       The routine may return for any of the following reasons:

       o  Memory allocation failure
       o  Incompatible version or illegal flags value

AUTHOR

       was developed by the Sendmail Inc.

SEE ASLO

       smfi_main(3N), smfi_setconn(3N), smfi_settimeout(3N), smfi_opensocket(3N), smfi_setbacklog(3N), smfi_setdbg(3N), smfi_stop(3N).

       on

																 smfi_register(3N)

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