Dynamic Allocation of Memory

1
Dynamic Allocation of Memory

• Lecture 4
• Secs 2.4, 3.2, 3.4
• Thu, Jan 24, 2008

2
Vectr Objects

• Non-empty Vectr
• Empty Vectr

3
The Vectr Class Interface

• The Vectr class interface
• vectr.h
• Related files
• vectr.cpp
• VectrTest.cpp

4
Allocation of Memory C Style

• The library function malloc() allocates a
  specified number of bytes of memory and returns a
  pointer to it.
• Include the header file ltcstdlibgt.
• Prototype

void malloc(int number-of-bytes)
5
Allocation of Memory C Style

• malloc() returns a pointer to the first byte of
  the allocated memory block.
• The returned pointer is a pointer to void.
• The returned pointer must be cast to the proper
  type.

int pi (int)malloc(sizeof(int)) Point2D pdt
(Point2D)malloc(sizeof(Point2D))
6
Deallocation of Memory C Style

• The library function free() deallocates memory.
• Include the header file ltcstdlibgt.
• Prototype
• The pointer must contain an address that was
  previously returned by malloc().

void free(void ptr)
7
Dynamic Memory for Arrays C Style

• Allocate memory for an array
• Deallocate memory for an array
• The computer remembers the size of the array.

Type ptr (Type)malloc(sizesizeof(Type))
free(ptr)
8
Example DynamicCArray.cpp
9
Allocation of Memory C Style

• Use the operator new.
• Allocate memory for a single object
• Allocate memory for an array of objects

Type ptr new Type
Type ptr new Typesize
10
Deallocation of Memory C Style

• Use the operator delete.
• Deallocate memory for a single object
• Deallocate memory for an array of objects
• The pointer must contain an address that was
  previously returned by new.

delete ptr
delete ptr
11
Example DynamicCArray.cpp
12
The Vectr Class Implementation

• The Vectr class implementation
• vectr.cpp

13
Example VectrTest.cpp