Not Getting Segmentation Fault [duplicate] - c

Question

This question already has answers here:
Why do I get a segmentation fault when writing to a "char *s" initialized with a string literal, but not "char s[]"?
(19 answers)
Closed 7 years ago.
Consider this simple code fragment :
{
if(fork())
{
printf("Parent terminated\n");
}
else
{
char *s = "hello world";
*s = 'H';
printf("child terminated\n");
}
wait(NULL);
return 0;
}
When I compile it I dont get a segmentation fault error as we expect while assigning to *s
The output is :
Parent Terminated ( without printing child terminated)
Now if I remove the two lines char *s=......'H' I get the normal output .Can someone please explain this

Answer 1

First of all, you aren't guarenteed to get a segmentation fault, or any defined behavior, for triggering undefined behavior, such as modifying a string literal. Though on Linux, string literals are put into read-only memory, so modifying them on Linux will usually result in a segmentation fault.
So why doesn't this code trigger a segfault? It does, but you just don't see it, because you forked.
The "Segmentation Fault (core dumped)" message is printed by your shell (ex. bash), when it detects, by calling wait, when the process it spawned terminates with a SIGSEGV (segfault) signal. However, your shell will not receive any notifications about child processes exiting; your parent process will.
Your parent process calls wait to wait and get the exit code when it terminates. If you weren't ignoring the exit code by passing in NULL to wait, you'd probably see that the exit code is -11, or -SIGSEGV.
So it is segfaulting; your parent process is just ignoring the child's notification that it segfaulted.

Answer 2

Firstly, what others said is correct: the behavior is undefined and you cannot depend on any behavior in particular when doing this.
However, I suspect what's happening is that the child actually is having a segmentation fault. However, the familiar "Segmentation fault" message you see in your terminal is actually printed by your shell when something you run seg faults.
But, since this is a child of something you ran, your shell didn't notice. If you have configured core dumps (e.g. ulimit -c unlimited) I expect you will find a core file from the seg faulted child process.