Question

Can anyone please help me understand the following code:

int d = 4;
printf(&d["Hay!Hello %c\n"], &4["BuddyWorld"]);           // Hello (some address in char)
printf(&d["Hay!Hello %c\n"], 4["BuddyWorld"]);            // Hello y
printf(&d["Hay!Hello %s\n"], 4["BuddyWorld"]);            // Segmentation fault
printf(&d["Hay!Hello %s\n"], &4["BuddyWorld"]);           // Hello yWorld

printf("d[Hay!Hello %s\n"], &4["BuddyWorld"]);      
/* warning: passing argument 1 of 'printf' makes pointer 
   from integer without a cast                           */

What is exactly the d[] or &d[] operator? (d is an integer)
Why does &4["BuddyWorld"] and 4[BuddyWorld] yields to different values? (‘W’ and ‘y’ respectively)

Answer 1

Subscripting in C is weird. a[b] is turned into *(a + b) (the thing at the address obtained by adding b to the pointer a). However, since a + b == b + a, it works the other way around as well (a[b] == b[a]). That’s all that’s going on. In particular, “HelloWorld” is really a pointer to a character array that stores the characters of the string.