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Memory Leaks and Dangling Pointers

Memory Leaks and Dangling Pointers. Lecture 5 Secs 2.4, 3.4 Mon, Jan 28, 2008. 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.

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Memory Leaks and Dangling Pointers

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  1. Memory Leaks and Dangling Pointers Lecture 5 Secs 2.4, 3.4 Mon, Jan 28, 2008

  2. 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.

  3. 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.

  4. Avoiding Dangling Pointers • It impossible to test a non-null pointer to see if it is dangling. • Always set pointers to NULL if they do not point to allocated memory. • Then compare them to NULL to see whether they point to allocated memory.

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

  6. Example: Vectr::input() • The input() function of the Vectr class must • Deallocate the memory that the Vectr 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.

  7. Example: Vectr::input() • vectr.h • vectr.cpp • VectrTest.cpp

  8. Constructors and the new Operator • The new operator is used in conjunction with the constructors. int* pi = newint(123); int* pai = new int[123]; string* ps = new string("Hello"); Rational* pr = new Rational(2, 3); Date* pd = new Date("Jan", 23, 2002); Point2D* ppt = new Point; Point2D* papt = new Point2D[10];

  9. Constructors and the new Operator • When using the new operator to create an array of objects, each object in the array is initialized through the default constructor.

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