Memory Leaks and Dangling Pointers

1. Memory Leaks and Dangling Pointers Lecture 6 Thu, Jan 29, 2004

2. Topics • Memory Leaks • Dangling Pointers • The Vector class SetSize() function • The Vector class Input() function • Constructors and the new Operator

3. Memory Leaks • A memory leak occurs when all pointers to a block of allocated memory have been lost. • Leaked memory cannot be accessed or reallocated. • Excessive memory leaks may cause the program to run out of usable memory and crash. • Memory leaks should always be avoided.

4. Example: Memory Leaks • Leak.cpp

5. Dangling Pointers • A dangling pointer is a non-null pointer that points to unallocated memory. • Dereferencing a dangling pointer may cause the program to crash. • It impossible to test a pointer to see if it is dangling. • Always set pointers to NULL if they do not point to allocated memory. • Dangling pointers must always be avoided.

6. Example: Dangling Pointers • Dangle.cpp

7. Example: Vector::SetSize() • The SetSize() function of the Vector class must • Allocate new memory of the specified size. • Copy the old values into the new memory. • Deallocate the memory that the Vector is currently using. • Redirect the Vector to the new memory.

8. Example: Vector::Input() • Example: vector.h, vector.cpp,VectorTest.cpp

9. Example: Vector::Input() • The Input() function of the Vector class must • Deallocate the memory that the Vector is currently using (if any). • Allocate new memory for the values to be input. • Continue to increase the allocated memory as more values are read.

10. Constructors and the new Operator • The new operator is used in conjunction with the constructors. int* pi = newint(123); string* ps = new string("Hello"); Rational* pr = new Rational(2, 3); Date* pd = new Date("Jan", 23, 2002); Point* ppt = new Point; int* pai = new int[123]; Point* papt = new Point[10];