What is meant by segmentation fault or memory fault in C?

Question

Following is my code and getting segmentation fault. Please help

#include<stdio.h>
#include<string.h>
main()
{
    char *p,str[100]="Hi, How Are You, Fine, Thank You";
    p=strtok(str,",");
    printf("%s\n",p);
    while(p != NULL)
    {
        p=strtok(NULL,",");
        printf("%s\n",p);
    }
}

O/p is:
Hi
How Are You
Fine
Thank You
and then Segmentation fault.

Answer 1

segmentation fault is a run-time error.
Whenever our program trying to access the memory location that we are not suppose to use then our program will get segmentation fault.
Ex:

#include<stdio.h>
main()
{
int *p;
printf("%d\n",*p); \\print the value present at that unknown memory location
}

-->In 1st step we have defined a pointer, pointer contains a garbage value.
-->In 2nd step we are printing the value which is present at unknown address that we are not suppose to do.

so it will give segmentation fault.

Answer 2

Segmentation fault is a fault that occurs because of illegal/invalid memory access.

Illegal memory access means, When a program tries to access a memory location that is not allowed or when a program tries to access a memory location in a way that is not allowed.