waiting for multiple childs - C - waitpid Post: 302500276

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Top Forums Programming waiting for multiple childs - C - waitpid Post 302500276 by wakatana on Monday 28th of February 2011 05:38:22 AM

02-28-2011

Registered User

waiting for multiple childs - C - waitpid

Hi gurus, I would like to fork more children and then write their return values: so far I tried:

Code:

#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>

int main(void)
{
        pid_t pid;
        int rv=0, i;
        pid_t child_pids[5];


        for (i=1; i<=5; i++){

                /* Multiple child forking */
                switch(pid = fork()){
                        case -1:
                                /* something went wrong */
                                /* parent exits */
                                perror("fork");
                                exit(1);

                        case 0:
                                /*Children process*/
                                child_pids[i] = getpid();
                                printf(" CHILD: number (and return value): %d PID: %d PPID: %d \n", i, getpid(), getppid());
                                exit(i);
                                break;

                                /*Missing code for parent process - will be executed out of loop*/
                }
        }
        /*Parent process*/
        if (pid!=0 && pid!=-1) {
                printf("PARENT: my PID is %d\n", getpid());

                for (i=1; i<=5; i++){
                        waitpid(child_pids[i], NULL, 0);
                        printf("PARENT: Child: %d returned value is: %d\n", i, WEXITSTATUS(child_pids[i]));
                }
        }
}

But returns any random variables for child process:

...
PARENT: Child: 3 returned value is: 13
PARENT: Child: 3 returned value is: 127
...

also tried following

Code:

int main(void)
{
        pid_t pid;
        int rv=0, i;
        pid_t child_pids[5];
        int child_state = 9;
        pid_t rc_pid;


        for (i=1; i<=5; i++){

                /* Multiple child forking */
                switch(pid = child_pids[i] = fork()){
                        case -1:
                                /* something went wrong */
                                /* parent exits */
                                perror("fork");
                                exit(1);

                        case 0:
                                /*Children process*/
                                //child_pids[i] = getpid();
                                printf(" CHILD: number (and return value): %d PID: %d PPID: %d \n", i, getpid(), getppid());
                                exit(i);
                                break;

                                /*Missing code for parent process*/
                }
        }
        /*Parent process*/
        if (pid!=0 && pid!=-1) {
                printf("PARENT: my PID is %d\n", getpid());

                for (i=1; i<=5; i++){
                        rc_pid = waitpid(child_pids[i], NULL, 0);
                        printf("PARENT: Child: %d returned value is: %d\n", i, WEXITSTATUS(child_pids[i]));
                }
        }
}

but returns always number 19 as return code of children
...
PARENT: Child: 4 returned value is: 19
...

Probably something something is wrong with waitpid() function
Thanks a lot.

wakatana

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LEARN ABOUT DEBIAN

ppmtosixel

ppmtosixel(1)						      General Commands Manual						     ppmtosixel(1)

NAME

       ppmtosixel - convert a portable pixmap into DEC sixel format

SYNOPSIS

       ppmtosixel [-raw] [-margin] [ppmfile]

DESCRIPTION

       Reads  a  portable  pixmap  as input.  Produces sixel commands (SIX) as output.	The output is formatted for color printing, e.g. for a DEC
       LJ250 color inkjet printer.

       If RGB values from the PPM file do not have maxval=100, the RGB values are rescaled.  A printer control header and a color assignment table
       begin the SIX file.  Image data is written in a compressed format by default.  A printer control footer ends the image file.

OPTIONS

       -raw   If  specified,  each  pixel  will  be explicitly described in the image file.  If -raw is not specified, output will default to com-
	      pressed format in which identical adjacent pixels are replaced by "repeat pixel" commands.  A raw file is often an order	of  magni-
	      tude larger than a compressed file and prints much slower.

       -margin
	      If  -margin  is not specified, the image will be start at the left margin (of the window, paper, or whatever).  If -margin is speci-
	      fied, a 1.5 inch left margin will offset the image.

PRINTING

       Generally, sixel files must reach the printer unfiltered.  Use the lpr -x option or cat filename > /dev/tty0?.

BUGS

       Upon rescaling, truncation of the least significant bits of RGB values may result in poor color conversion.  If the original PPM maxval was
       greater	than  100,  rescaling  also reduces the image depth.  While the actual RGB values from the ppm file are more or less retained, the
       color palette of the LJ250 may not match the colors on your screen.  This seems to be a printer limitation.

SEE ALSO

       ppm(5)

AUTHOR

       Copyright (C) 1991 by Rick Vinci.

								   26 April 1991						     ppmtosixel(1)

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