Chapter 8.4, Problem 8.4PP

A.

Program Plan Intro

Given code:

//Include necessary header files

#include <stdio.h>

#include "csapp.h"

//Define a main function

int main()

{

//Variable declaration

int status;

pid_t pid;

//Print the statement

printf("Hello\n");

//Call the method fork() and assign it to the variable pid

pid = fork();

//Print the statement

printf("%d\n",!pid);

//Check, pid is not equal to zero

if (pid != 0)

{

//True, check the condition

if (waitpid(-1, &status, 0) > 0)

{

//True, check the condition

if (WIFEXITED(status) != 0)

//True, print the statement

printf("%d\n" , WEXITSTATUS(status));

}

}

//Otherwise, print the statement

printf("Bye\n");

//Exit

exit(2);

}

Explanation:

The given code is used to print the number of output lines and possible outputs.

In the given code, the variable “status” and “pid_t pid” are declared.

• The main program first print the output line “Hello”.
• Then, call the function “fork()”, which is called once and return twice.
• Print the value that is not equal to the variable “pid”.
• The “if” condition check, the variable “pid” is not equal to “0”.
  • True, “if” condition check, “(waitpid(-1, &status, 0) > 0)”.
    • True, “if” condition check, “(WIFEXITED(status) != 0)”.
      • True, print the value of “WEXITSTATUS(status)”.
• Print the statement “Bye”.
• Exit from the program.

B.

Explanation of Solution

Possible ordering of the output lines:

Possible output sequence corresponding to the process graph is as follows:

Hello