Question

Code:

#include "stdio.h"
#include "string.h"

int main()
{
  char *p = "abc";
  printf("p is %s \n", p);
  return 0;
}

Output:

p is abc

---

Code:

#include "stdio.h"
#include "string.h"

int main()
{
  char *p = "abc";
  strcpy(p, "def");
  printf("p is %s \n",p);
  return 0;
}

Output:

Segmentation fault (core dumped)

Could someone explain why this happens?

Answer 1

Because p is pointing to read only memory.

Overwriting data that p points to results in undefined behavior.
A string literal is any string you specify explicitly in quotes. All string literals are read only. (Note: You can use a string literal to initialize a char array.)

You need to instead allocate your own buffer like this:

char buffer[4];
strcpy(buffer, "def");
printf("buffer is %s \n", buffer);