$4.$ Waiting for a Process $1\%$

We can make a parent process waiting for its child to finish before continuing by using wait:

#include

#include

pid$\_$t wait $($int $*$stat$\_$loc$)$;

The status information is written to stat$\_$loc.

Try the following program:

$//$test$\_$wait.cpp

#include

#include

#include

#include

#include

#include

using namespace std;

$10$

int main$()$

$\{$

pid$\_$t pid; $//$process id

char $*$message;

int n;

int exit$\_$code;

cout $<<$ "fork program starting

$"$;

pid $=$ fork$()$;

switch $($pid$)\{$

case $-1$:

cout $<<$ "Fork failure!

$"$;

return $1$;

case $0$:

message $=$ "This is the child

$"$;

n $=5$;

exit$\_$code $=9$;

break;

default:

message $=$ "This is the parent

$"$;

n $=3$;

exit$\_$code $=0$;

break;

$\}$

for $($int i $=0$; i $<$ n; $++$i$)\{$

cout $<<$ message;

sleep $(1)$;

$\}$

$//$waiting for child to finish

if $($pid $!=0)\{//$parent

int stat$\_$val;

pid$\_$t child$\_$pid;

child$\_$pid $=$ wait $($&stat$\_$val$)$; $//$wait for child

$11$

cout $<<$ "Child finished: PID $="<<$ child$\_$pid $<<$ endl;

if $($WIFEXITED $($stat$\_$val$))$

cout $<<$ "child exited with code $"<<$ WEXITSTATUS $($stat$\_$val$)<<$ endl;

else

cout $<<$ "child terminated abnormally!" $<<$ endl;

$\}$

exit $($exit$\_$code$)$;

$\}$

Requirement:

Run the program and explain what you have seen on the screen.

Modify the program so that the child process creates another child and waits for it$.$ The grandchild prints

out the IDs of itself, its parent and grandparent.