CS304: Lecture 4

1
CS304 Lecture 4

• Pointers and Pointer-Based Strings
• Deitel, Ch. 8 (part 1)
• http//www.cis.uab.edu/cs304

2
What are pointers?

• Pointers are types that store memory addresses
• include ltiostreamgtusing namespace stdint
  main() int x, y, ptr 0 // ptr is
  a pointer ptr x // x address of
  x cout ltlt ptr ltlt , ptr y
  cout ltlt ptr ltlt endl return 0
• Output 0xffbef44c, 0xffbef448 // 0x means
  hexadecimal

3
Case Study

• Please take some time to go through the Case
  Study on Card Shuffling and Dealing Simulation.
  Its rich with concepts explored today.

4
Potential Points of Confusion

• Using in the declaration of a pointer is NOT an
  operator
• It is possible to have a interpreted as a unary
  (next slide) or binary operator, but only when
  not involved in a declaration.
• If uninitialized, pointers should be set to zero
  or NULL (defined in iostream)

5
Pointer Operations

• The address operator (or address-of
  operator)
• Takes any variable and provides a pointer-value
  for that variable
• int ptr variable
• The indirection operator (or dereferencing
  operator)
• Takes a pointer variable and provides a synonym
  name, if you prefer to view it that way.
• After the above, (ptr variable), and cout ltlt
  ptr outputs the value of variable
• x somevalue is legal.

6
Pointers and Pass-By-Reference

• There are two types of pass-by-reference
  pass-by-reference with reference arguments, and
  pass-by-reference with pointer arguments.
  (Confused yet?)
• One can declare a function that takes a pointer
  as an argument, like so
• void cubeit(int n) n n n n
  //Ewww
• Hint Parentheses clear things up
• void cubeit(int n) n (n) (n) (n)

7
Food for thought

• Passing an array by reference?
• An array declaration is really a const pointer to
  the beginning of a block of memory, so it is
  automatically passed by reference.

8
Obvious Question References vs. Pointers

• This isnt important yet, but
• Pointers were a C feature, References are a C
  feature (as well as Java)
• Some of the other features of C (that we
  havent learned about yet) do not quite work as
  well with pointers as with references
• References look prettier!
• However, references are constant. This will
  become a downfall later.

9
A Quick Lesson in Pointer Arithmetic

• int x10//Note that x is a pointer
• x1 (x1) //both access the next data
  //element in the array
• int y x
• y y x1
• y y x2
• y - 3 y x - 1, unfortunately.

10
Types of Const for Pointers

• Non-constant pointer to non-constant data
• char a
• Non-constant pointer to constant data
• const char a
• Constant pointer to non-constant data (Array)
• char const a
• Constant pointer to constant data
• const char const arr

Non-const Mutable !!
11
Interview Question
charconst a char b a
b //? ba //?
const char a char b a
b //? ba //?
X
X
0xffbef44c
20
0xffbef44c
20
y
y
0xffbef448
10
0xffbef448
10