Program output overflows Post: 302306103

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Top Forums UNIX for Dummies Questions & Answers Program output overflows Post 302306103 by hansel13 on Saturday 11th of April 2009 03:20:08 AM

04-11-2009

Registered User

Program output overflows

I Wrote code that forks into two processes, a parent process, and a child process. The parent process will take the arguments to main() and send them one character at a time to the child process through a pipe (one call to write for each character). The child process will count the characters sent to it by the parent process and print out the number of characters it received from the parent.

The child should return normally (in other words, do not have the parent kill the child).

For some reason when my program executes, once in a while the command line prompt will come up before my program is done outputting. so basically the commandline gets a line of my output.. So I just press enter and everything is OK.

Code:

#include <stdlib.h>
#include <string.h>
#include <stdio.h>    /* standard I/O routines.                */
#include <unistd.h>   /* defines pipe(), amongst other things. */

#define ARRAY_SIZE 1000

int main(int argc, char* argv[])
{
    int data_pipe[2];
    int pid;
    int i = 0;
    char readbuffer[ARRAY_SIZE];
    char *in_str; /*= argv[1];*/

    for(i = 0; i < sizeof(readbuffer); i++)
        readbuffer[i] = 0;

    for(i = 1; i < argc; i++)
    {
        if(i > 1)
        {
            argv[i] = strncat(argv[i - 1],argv[i],1000);
        }
    }

    if(argc > 1)
        in_str = argv[i - 1];

    //printf("Printing string: %s\n", argv[i - 1]);
    //printf("The sentence entered is %u characters long.\n",strlen(argv[i - 1]));

    /* first, create a pipe. */
    pipe(data_pipe);

    /* now fork off a child process, and set their handling routines. */
    pid = fork();

    if(pid == -1)       /* fork failed. */
    {
        perror("fork");
        exit(1);
    }
    else if(pid == 0)           /* inside child process. */
    {
        close(data_pipe[1]);
        read(data_pipe[0], readbuffer, sizeof(readbuffer));
        printf("child: counted %d characters\n", strlen(readbuffer));

        //for(i = 0; i < 30; i++)
        //      printf("%d:  %c\n", i, readbuffer[i]);
        //printf("Received String: %s\n", readbuffer);
        sleep(5);
        exit(0);
    }
    else /* inside parent process */
    {
        close(data_pipe[0]);
        while (*in_str != '\0')
        {
            in_str++;
            write(data_pipe[1], &in_str, 1);
        }
        exit (0);
    }

    return 0;
}

hansel13

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LEARN ABOUT HPUX

preap

preap(1)                                                           User Commands                                                          preap(1)

NAME

       preap - force a defunct process to be reaped by its parent

SYNOPSIS

       preap [-F] pid...

DESCRIPTION

       A  defunct  (or  zombie)  process  is one whose exit status has yet to be reaped by its parent. The exit status is reaped via the wait(3C),
       waitid(2), or waitpid(3C) system call. In the normal course of system operation, zombies may occur, but are typically short-lived. This may
       happen  if a parent exits without having reaped the exit status of some or all of its children. In that case, those children are reparented
       to PID 1. See init(1M), which periodically reaps such processes.

       An irresponsible parent process may not exit for a very long time and thus leave zombies on the system. Since the operating system destroys
       nearly all components of a process before it becomes defunct, such defunct processes do not normally impact system operation. However, they
       do consume a small amount of system memory.

       preap forces the parent of the process specified by pid to waitid(3C) for pid, if pid represents a defunct process.

       preap will attempt to prevent the administrator from unwisely reaping a child process which might soon be reaped by the parent, if:

         o  The process is a child of init(1M).

         o  The parent process is stopped and might wait on the child when it is again allowed to run.

         o  The process has been defunct for less than one minute.

OPTIONS

       The following option is supported:

       -F       Forces the parent to reap the child, overriding safety checks.

OPERANDS

       The following operand is supported:

       pid      Process ID list.

EXIT STATUS

       The following exit values are returned by preap, which prints the exit status of each target process reaped:

       0        Successfully operation.

       non-zero Failure, such as no such process, permission denied, or invalid option.

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE         |      ATTRIBUTE VALUE        |
       +-----------------------------+-----------------------------+
       |Availability                 |SUNWesu (32-bit)             |
       +-----------------------------+-----------------------------+
       |                             |SUNWesxu (64-bit)            |
       +-----------------------------+-----------------------------+

SEE ALSO

       proc(1), init(1M), waitid(2), wait(3C), waitpid(3C), proc(4), attributes(5)

WARNINGS

       preap should be applied sparingly and only in situations in which the administrator or developer has confirmed that defunct processes  will
       not be reaped by the parent process. Otherwise, applying preap may damage the parent process in unpredictable ways.

SunOS 5.10                                                          26 Mar 2001                                                           preap(1)