CS50 Week 4 Memory, when we don't reference a address to a string does it come automatically?

Question

Does the char* already contain a address to the first char in this example?

When we do scanf is the 2nd parameter a real address?

#include <stdio.h>

int main(void)
{
    char *s;
    printf("s: ");
    scanf("%s", s);
    printf("s: %s\n", s);
}

Answer 1

No, and trying to populate it with a call to scanf("%s", s) is undefined behavior because the pointer does not point to allocated memory.

You may initialize s by allocating it:

    s = malloc(100);
    if(NULL == s)
    {
         goto cleanup; // one of the few valid uses of goto in C
    }
     
    if(scanf("%99s", s) != 1) 
    {
        // scanf failed to populate 's'
        goto cleanup;
    }

    printf("Hello %s\n", s);
    
cleanup:
    free(s);
    s = NULL;