Quiz 4 Pointers and Dynamically Allocated Memory

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Quiz 4Pointers and Dynamically Allocated Memory

• CGS 3460, Lecture 32
• Mar 31, 2006
• Hen-I Yang

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Previously

• Arrays and Pointers

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Agenda

• Dynamic Memory Allocation
• Dynamic Allocated Arrays

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Why dynamically allocate memory?

• Use of lots of variables
• Use of arrays
• Some flexibility, but not enough
• Has to prepare for the worst
• Waste of memory space not used
• Use of dynamically allocated memory
• Most frequently associated with array, string and
  struct

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How to dynamically allocate memory?

• ltstdlib.hgt
• malloc(size_t size)
• There are other functions, but malloc is by far
  most frequently used
• It allocates, but not clears
• If no memory of the size available, will return
  null
• It is programmers responsibility to check for
  null

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Dynamically allocated array

• Difficulty in estimating the proper size of array
  ahead of time.
• Dynamically means you can decide the size
  during the execution time, not compilation time
• Close relations between arrays and pointers in C,
  make it almost as easy to operate as the original
  array

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Malloc an Array

• int a
• a malloc(n sizeof(int))
• Can we just say a malloc(n 4)?
• Not a good idea
• After malloc, you have all the space needed for
  the array allocated
• After that, you can use ai or (ai) to access
  the elements

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Summary

• Dynamic Memory Allocation
• Dynamic Allocated Arrays

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Before you go

• Read Chapter 17
• Exercise Have a look at 17.12