Lab 10 Solution

Lab 10 is on pointers. It covers: addresses, pointers, the heap, dynamic memory allocation (new, delete, delete []) It also has a very brief introduction to linked lists, a basic data structure.




With assistance from the provided startup code, create a program that uses memory as shown in the memory diagram below. Wherever possible, set the values of all variables indirectly using pointers. Use pointer dereferencing to set the values of the "pointed to" variables. You can "dereference" pointers with the '*' operator. For example, to set price to $19.95, do NOT use the variable price. Instead, use the pointer variable *p_price. To set pi_div_2, dereference p_PI to get 3.141592, divide it by two, and place the result into PI_div_2.




To create the "linked list" containing Person "Harry" and Person "Sally", you need the following data structure. You should enhance this, as desired, with constructors, setters, etc.




class Person { string name; Person *next; };




// name of the person




// pointer to the next person in the list



To create instances of Person, you will use:




static allocation: Person wizard will be on the stack;



dynamic allocation: Persons "Harry" and "Sally" are allocated on the heap









To manipulate an object of class Person, you need to create some constructors, getters and setters to fill in the name and set the pointers, or, you could make the data members public and use "dot" notation, such as: Person wizard; wizard.name="Gandalf"; wizard.next=nullptr; For dynamically allocated instances, you can use arrow notation, such as: personList - name="Harry".




The keyword nullptr is the correct C++11/14/17 way to set a pointer to nothing; do NOT use NULL or 0.




To create variables on the heap, with no names, you have to use new to dynamically allocate the memory. See sample output (bottom page). IMPORTANT: Every new should be matched by a delete to prevent a memory leak!




IMPORTANT: Make sure you delete all memory you dynamically allocate before leaving main(). Don't allow any memory leaks. Match all new with delete. When deleting an array, remember to use delete [] array.




After items are placed in memory, use cout statements to output the addresses and values of all variables. Output the addresses of all variables (both pointer and named) in hexadecimal format, and output the contents (values) of all int, float, double and string variables.




You cannot force the memory layout to be exactly in the order as shown below. As a programmer, you don't control exactly WHERE in memory the compiler places variables. The important thing is for you to create the pointer variables, value variables, and set them up (nearly) as shown below.










more










RAM


RAM










(stack)


(heap)


































to place items in heap, use new






―┐








float
*p_price
●─




to remove items from heap, use delete






│




use new, then delete to avoid memory leak
float
price
$19.95
←┘




Ф is nullptr








―┐










double
*p_PI
●─










double
PI_div_2
1.570796
│










double
PI
3.141592
←┘
















―┐










int
*p_size
●─










int
maxSize
5028
←┘










int
*p_amount
●─
――
1234
<no name












――








int
*pArray
●─
11
<no name
3 element array of int








22
<no name
























Person
*emptyList
Ф


33
<no name
























Person
wizard
"Gandalf"


































Ф
























head of linked list


















Person
*personList
●─
――
"Harry"


string
name










●─
―┐
Person
*next












│














"Sally"
←┘
string
name










Ф


Person
*next














NULL-terminated list




































Expected output from Lab10 on pointers: NOTE: Your addresses may be different!




Output from Lab10 memory diagram on pointers:




address of price is: &0x22fe18 contents of price is: 19.95




address of p_price is: &0x22fe10 contents of p_price is: 0x22fe18




The contents of *p_price is: 19.95




address of PI is: &0x22fe08 contents of PI is: 3.14159




address of PI_div_2 is: &0x22fdf8 contents of PI_div_2 is: 1.5708




address of p_PI is: &0x22fe00 contents of p_PI is: 0x22fe08




The contents of *p_PI is: 3.14159




address of maxSize is: &0x22fdf4 contents of maxSize is: 5028




address of p_size is: &0x22fde8 contents of p_size is: 0x22fdf4




The contents of *p_size is: 5028




address of p_amount is: &0x22fde0 contents of p_amount is: 0x355bf0




The contents of *p_amount is: 1234




After delete, the contents of p_amount is: 0x355bf0




After reset to nullptr, the contents of p_amount is: 0




address of pArray is: &0x22fdd8 contents of pArray is: 0x355bf0




address of pArray[0] is: &0x355bf0 contents of pArray[0] is: 11




address of pArray[1] is: &0x355bf4 contents of pArray[1] is: 22




address of pArray[2] is: &0x355bf8 contents of pArray[2] is: 33




After delete [], the contents of pArray is: 0x355bf0




After reset to nullptr, the contents of pArray is: 0




address of emptyList is: &0x22fdd0 contents of emptyList is: 0




static (uses: Person wizard):




address of wizard is: &0x22fdc0




address of wizard.name is: &0x22fdc0 contents of wizard.name is: Gandalf




address of wizard.next is: &0x22fdc8 contents of wizard.next is: 0




dynamic (uses: personList, Person("Harry"), Person("Sally"):




address of personList is: &0x22fdb8 contents of personList is: 0x355c20




address of personList-name is: &0x355c20 contents of personList-name is: Harry




address of personList-next is: &0x355c28 contents of personList-next is: 0x3565f0 <follow link to next Person on personList




address of personList-next-name is: &0x3565f0 contents of personList-next-name is: Sally




address of personList-next-next is: &0x3565f8 contents of personList-next-next is: 0