CSCI 255 Pointers in C

Pointers and arrays

• Lvalues and Rvalues
• & — address-of operator
• * — indirection (or dereference) operator
• If P is a pointer to an integer, then P+i is a pointer to the i’th integer after the integer referenced by P.
• P[i] is *(P+i).
• If P is an array of integers, then P is a constant pointer to an integer.
• P++ increments p to point to the next integer in memory.
• NULL in C is similar to null in Java.
• Pascal had pointers: @P for &P and P^ for P* .

It only gets worse

Suppose both P and Q are pointers to integers.

• (int) &P[5] is (int) P + 5 * sizeof(int)
• (int) &P[5] - (int) &P[3] is 2 * sizeof(int)
• P+i and P-i and P<Q and P>Q and P++ and P-- are only defined if the relevant pointers are elements of the same array
  • or one past the end of the array
• P + Q is not allowed for pointers
• void * is the type of a generic pointer
• (long) (void *) &P[5] is weird but implies intent

Trying it out

Take a look at Problem 16 from the Fall 2014 Final exam.