Question

I’m trying to learn C, and now I’m playing with structures.
I have the following piece of code:

#include <string.h>

struct user {
  unsigned int utime;
  char *username;
};

void main()
{
  char username[] = "root";
  struct user *u;
  strcpy(u->username, username);
}

But, when I try to run it, it generates a Segmentation fault.
What’s wrong with it?

Answer 1

u is a pointer to a struct but you didn’t allocate any memory for it yet. The line must be
struct user *u = malloc(sizeof(struct user)). Additionally you will also have to allocate memory for the username pointer within your struct before calling strcpy.