get the status of the child process

This is a discussion on get the status of the child process within the C Programming forums, part of the General Programming Boards category; i want to get the status of child process (when execvp is failed) in the father process so im useing ...

  1. #1
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    get the status of the child process

    i want to get the status of child process (when execvp is failed) in the father process so im useing the next code: (im programming on linux)
    Code:
    pid=fork();
    if(pid==0)
    {
    if(execvp(com[0],com)==-1)
    exit(-1);
    }
    else
    {
    waitpid(pid,&status,0);
    }
    but the value of status is stay a junk number.
    can someone help me in this problem ?
    thanks !

  2. #2
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    If you set status to 0 before calling waitpid() does it still contain 0 afterwards?
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  3. #3
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    Quote Originally Posted by mystic-d View Post
    Code:
    if(execvp(com[0],com)==-1)
    exit(-1);
    wait();
    your child is getting exit as soon as it spawns a new process using execvp( )..
    and parent gets the same with signal, the process spawned by execvp( ) is still running..
    and is in zombie state..

    try the 'wait();' and see it must be stopped till the execvp process returns..
    C's Motto: who cares what it means? I just compile it!!

  4. #4
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    Quote Originally Posted by gibsosmat View Post
    your child is getting exit as soon as it spawns a new process using execvp( )..
    and parent gets the same with signal, the process spawned by execvp( ) is still running..
    and is in zombie state..

    try the 'wait();' and see it must be stopped till the execvp process returns..
    What? You can't do wait() after exit() - because you never get there.

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  5. #5
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    Quote Originally Posted by matsp View Post
    What? You can't do wait() after exit() - because you never get there.

    --
    Mats
    its the else case not inside the if( )..
    so that the child will wait for execvp( )
    I think his problem being invalid pid provided to waitpid( )..
    if we put wait( ); there it will wait till the execvp is done well..

    if you just want to see what the status of the execvp( ) from parent process I think this is not what he should do..
    C's Motto: who cares what it means? I just compile it!!

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    i was set status to be zero before the "waitpid" and afterwards its have the value: "65280".

    (but i want to get "-1"..)

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    Code:
    #include <unistd.h>
    #include <signal.h>
    ...
    pid=fork();
    if(pid==0)
    {
         if(execvp(com[0],com)==-1)
            {
                printf("execvp failed\n");
                pause();
               exit(-1);
            }
    }
    else
    {
        waitpid(pid,&status,0);
        printf("Status: &#37;d\n",status);
        kill(pid, SIGINIT);
    }
    try this..
    Last edited by gibsosmat; 11-16-2007 at 10:10 AM.
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  8. #8
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    If you look at the manual page, there are a bunch of macros which extract the true exit status of the child process from some other information which is all encoded into the same integer.

    > afterwards its have the value: "65280".
    Which is FF00 in hex, so your -1 is in there somewhere - see the macros!
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
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  9. #9
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    i tryed all the macros and cant get it work...
    any help will be aperciated...
    thanks !

  10. #10
    and the hat of wrongness Salem's Avatar
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    Tried how?
    Show us what you did.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
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