CODEWITHSUNDEEP
csignalsfork
Lazarus
Lazarus

Reputation: 125

c reporting which signal terminated a child

I've been working on a shell pretty extensively, and now I'm trying to upgrade this code to report when a child has been terminated by a signal (other than SIGINT). I'm also trying to report a "core dump" if one happened in parenthesis (similar to bash).

   ...

   if(test == -1){ 
      cpid = fork();
      if(cpid < 0){
         //Fork wasn't successful 
         perror("fork");
         free(argList);
         return -1;
      }

      if(cpid == 0){
         //We are the child!
         close(pipefd[0]);
         dup2(pipefd[1], 1);

         execvp(args[0], args);         
         //execvp returned, wasn't successful
         perror("exec");
         fclose(stdin);  
         exit(127);
      }
      close(pipefd[1]);

      //Have the parent wait for child to complete, if flags allow 
      if(strcmp(flags, "NOWAIT") != 0){

         if(wait (&status) < 0){
            //Wait wasn't successful
            perror("wait");
         }
         else{


////////////////////////////////////////////////////////
        //report if a child has been terminated by a signal other than SIGINT
        if((WIFSTOPPED(status) && (WSTOPSIG(status) != SIGINT))){

           printf("child terminated by signal [%d]\n", WSTOPSIG(status));

           if(WCOREDUMP(status)){
              printf("core dumped\n");
           }
        }
//////////////////////////////////////////////////////////

           free(argList);
           //since no child is running, return 0
           return 0;
         }
      }
      else{
         //if a child is running, return the child's pid
         return cpid;
      } 
   }

   ...

I'm not really sure how to proceed with this. This is my first time working this extensively with the fork() command and my knowledge of the parent-child relationship is pretty shoddy, to tell the truth. I've searched for answers and the closest I've gotten is that SIGCHLD handles this sort of thing, but I need to be able to print out a specific number. something like:

printf("child terminated (%d)\n", 15 + signal);

edit*
I put what I think to be the correct implementation of what I want into the code, surrounded by ////////

Upvotes: 2

Views: 2841

Answers (1)

Jonathan Leffler
Jonathan Leffler

Reputation: 754080

You collect the status of the child with your chosen variant of wait() or waitpid() — or on BSD wait3() or wait4() if you like — and then analyze the status.

POSIX provides:

  • WIFEXITED(status) — returns true if the program exited under control.
  • WEXITSTATUS(status) — returns the exit status (0..255).
  • WIFSIGNALED(status) — returns true if the program exited because of a signal.

  • WTERMSIG(status) — returns the terminating signal.

  • WIFSTOPPED(status) — if the child was stopped by a signal.

  • WSTOPSIG(status) — the signal that stopped the child.
  • WIFCONTINUED(status) — if the child has continued since a stop signal.

POSIX does not define, but many Unix-based implementations provide:

  • WCOREDUMP(status) — returns true if a core was dumped.

Upvotes: 5

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