program代写、代做C/C++编程设计

日期：2024-11-06 09:49

Introduction

In this lab, you will deepen and solidify the concept of pointers through the concept of a

doubly-linked list data structure. You will implement a library to create, modify, and delete linked

lists. You will also learn to allocate and deallocate space during runtime. Finally, you will use

your library to compare two algorithms for counting unique words in a list. This lab will be

completed on both the Nucleo development kit and Linux.

Reading

● K&R – Chapters 5, 6.7, 7.8.5, appendix B5

Concepts

● Doubly-linked lists

● Memory allocation

● Sorting

● Pointers (including NULL)

● Algorithmic analysis

Required Files:

● LinkedList.c

● LinkedListTest.c

● sort.c

● README.pdf

BOARD OF STUDIES IN COMPUTER ENGINEERING

Linked Lists

20 Points

Lab Files:

● DO NOT edit these files:

o LinkedList.h – Contains the spec and prototypes for the linked-list functions you

will implement.

o BOARD.c/h – Standard hardware library for ECE013.

o stopwatch.c/h – Tools for benchmarking the execution time of your program.

o Lab06_main.c – Default Makefile target; contains the main() function that you

will use to benchmark the algorithms that you develop in sort.c.

o GNUmakefile — Used for compiling this lab on Linux.

● Edit these files:

o sort.c – This file contains some starter code for a demonstration of the testing

for the sorting algorithms along with a function to generate a word list for the

sorts to operate on.

▪ It is included as sort_template.c

● Create these files:

o LinkedList.c – Implement the library described in LinkedList.h.

o LinkedListTest.c – A test harness for your LinkedList library. Should include a

main().

Assignment requirements

● Your program will implement the functions whose prototypes are provided in

LinkedList.h. The functions all have appropriate documentation and describe the

required functionality.

● Within LinkedListTest.c you will:

o Create a test harness that tests your linked list functions and ensures

that they return the correct values. As in previous labs, at least two tests

are required per function.

o Once you are done testing the functionality of LinkedList.c, you will need

to exclude LinkedListTest.c from the project.

● Within sort.c you will:

o Implement two algorithms for sorting linked lists inside the functions

SelectionSort() and InsertionSort(). You will use these with the

provided main() code to perform timing experiments that will

(hopefully) demonstrate the usefulness of linked lists. You should not

modify either main() or CreateUnsortedList() in this file.

● Add inline comments to explain your code.

● Create a readme file and export it to PDF named README.pdf containing the

following items. Spelling and grammar count as part of your grade so you'll want

to proof-read this before submitting. This will follow the same rough outline as a

lab report for a regular science class. It should be on the order of three

paragraphs with several sentences in each paragraph.

o First you should list your name & the names of colleagues who you have

collaborated with.

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o Report the results of the timing experiment in sort.c. Which was faster,

SelectionSort() or InsertionSort()? Explain why. Was this what you

expected? How does performance compare on Linux vs your Nucleo?

o In the next section you should provide a summary of the lab in your own

words. Highlight what you thought were the important aspects of the

lab. If these differ from how the lab manual presents things, make a

note of that.

o The following section should describe your approach to the lab. What

was your general approach to the lab? Did you read the manual first or

what were your first steps? What went wrong as you worked through it?

What worked well? How would you approach this lab differently if you

were to do it again? How did you work with other students in the class

and what did you find helpful/unhelpful?

o The final section should describe the results of you implementing the

lab. How did it end up finally? How many hours did you end up spending

on it? What did you like about it? What did you dislike? Was this a

worthwhile lab? Do you have any suggestions for altering it to make it

better? What were the hardest parts of it? Did the points distribution for

the grading seem appropriate? Did the lab manual cover the material in

enough detail to start you off? Did examples or discussions during class

help you understand this lab or would more teaching on the concepts in

this lab help?

1 NOTE: collaboration != copying. If you worked with someone else, be DETAILED in your

description of what you did together.

● Make sure that your code triggers no errors or warnings when compiling as they

will result in a significant loss of points.

● Follow the style guidelines.

Doing this Lab on Linux:

For this lab we will continue using the make system. The commands as before are

below. For this to work the file ‘GNUmakefile’ needs to be in the same directory as

the rest of your files, it is only used when compiling on Linux.

● $ make

o This command will create the final executable named Lab06

● $ make LinkedListTest

o This command will compile your linked list test harness into the

executable LinkedListTest

Grading:

This assignment consists of 20 points:

● 8.5: Automated Components:

o 6.5 – LinkedList library

▪ 3.5 = 0.5 points per function for each of LinkedListNew(),

LinkedListCreateAfter(), LinkedListCreateBefore(), LinkedListRemove(),

LinkedListSize(), LinkedListGetFirst(), LinkedListGetLast(), and

LinkedListData().

▪ 1.0 point, all functions handle null pointer inputs

▪ 1.0 point, all functions that allocate can handle malloc() failures

▪ 0.5 no functions reference deallocated data

▪ 0.5 no functions allocate unnecessary memory

o 2.0 – Sort.c

▪ 1.0 SelectionSort() gives correct results, and does not print.

▪ 1.0 InsertionSort() gives correct results, and does not print.

● 11.5: Human components:

o 0.5 -- LinkedListPrint()

o 4.0 -- Test harness for LinkedList

▪ 1 point for testing each function.

▪ 1 point for thorough and diverse tests.

▪ 1 point for readability of output.

▪ 1 point for correctly performing the timing experiment on

SelectionSort() and InsertionSort(), then reporting your results in

README.pdf.

o 1.0 sort.c:

▪ 1 – explanation in README.pdf is clear, accurate, and demonstrates

understanding of why linked lists are useful.

o 1.5 points – Readability and code style

o 4.5 points – Lab writeup

● Deductions:

o NO CREDIT for sections where required files don't compile

o -1 changing the name of a prototyped function in sort.c (this will break our

autochecker scripts!)

o -2: At least one compilation warning

o -2: Extremely bad coding practice (Used extern or goto, extreme inefficiency or

unreadability)

o Other deductions at grader’s discretion.

o It must compile within Visual Studio Code/PlatformIO and Linux using the C11

standard. Code that does not compile will receive no credit.

Pointers

Pointers are covered thoroughly in the required reading for this lab, so if you are having

trouble, refer back to chapter 5 of K&R. However, there is one concept about pointers

that is not directly addressed in the reading: null pointers. A null pointer is a pointer to

nothing. These pointers must be handled as a special case if they are passed to a

function that expects non-null data pointers. This is one of the major sources of crashes

in programs.

The main problem with null pointers arises from when you try to dereference them

(assuming x is an int pointer and equal to NULL): *x = 6;

The reason for why becomes clear when you think about what memory location x points

to. 0, or NULL, is an invalid memory location, and a "null pointer dereference" error

occurs because there is no memory location to write to, so an error occurs. This is a

"fatal" error, which means that the program has no way to handle it, so the only thing it

can do is crash! This is a common cause of Windows blue-screen-of-death errors (when

this dereferencing happens in kernel space

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). The solution to this is to check for null

pointers before dereferencing. An especially important case for checking to see if a

pointer is null is after any call to malloc() or calloc(), which we will cover a little later.

Doubly-linked lists

In computer programs, much as in real life, keeping a list of things can be useful. Usually

the number of items that will be in this list is known ahead of time and so in a computer

program this list could be kept in a standard C array. There will be occasions, like when

processing user input, when the number of items to be stored in a list is not known

ahead of time. This is a problem with C’s statically-allocated arrays. The common

solution is to use another data type called a linked list.

Linked lists are exactly what they sound like: a collection of objects that are all linked

together to form a single list. As each item is linked to at least one other item in the list

there is a set ordering to the list: from a “head” item at the start to a “tail” item at the

end. Since these items are all connected it is easy to access any item from any other item

by just traversing or “walking” through the list.

For this lab you will be implementing a doubly-linked list, the more useful sibling of the

linked lists. A doubly-linked list is also straightforward: each item is linked to both the

item before it and after it. This allows for traversal of the list from any element to any

other element by walking along it, which makes using the list very easy.

2Note that kernel space vs user space is a key concept in protected mode multitasking operating systems

such as Linux and WinNT derivatives. Using protected mode, a misbehaving user program cannot (in

theory) crash the entire system. The absence of protected mode is a key property of embedded systems.

The items in the list you are implementing are stored as structs in C because they will

be storing a few different pieces of data. Specifically it holds a pointer to the previous

ListItem, which will be NULL if it is the head of the list; a pointer to the next

ListItem, which will be NULL if it’s at the end of the list; and a pointer to any kind of

data (NULL if there’s no data). The typedef and the name after the “}” let you refer to

the struct in a similar fashion to any other data type, by using the single name

“ListItem” instead of the longer “struct ListItem”.

The definition of the ListItem struct in LinkedList.h:

typedef struct ListItem {

struct ListItem *previousItem;

struct ListItem *nextItem;

char *data;

} ListItem;

Now that you understand the structure of a linked list we will introduce the various

operations that can be performed upon a list. The standard operations are creating a

new list, adding elements to a list, finding the head of a list, and removing elements

from a list.

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Creating a new list: A new list is created by just making a single ListItem. As this ListItem

is both the head and tail of the list there is no item before it or after it in the list.

Adding to a list: Now that you have a list, how do you add more elements to it? With the

arrays that you are familiar with, you need to know two things: the position to insert into

and the data that will be inserted. With linked lists it’s a little different because there’s

never a “free spot” to insert a new item into. What is done instead is that the position of

the new list item is relative to an existing item, generally the item before it in the list. So

to insert an item into the list, that item is inserted after an existing item. If the list went

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It is incredibly useful to your understanding to draw this out on a piece of paper or a white board. Make

boxes for each member of the struct, and use arrows to point to the next list element and the previous

ones (in other words, use arrows to show what the pointers point to). Go through all of the functions and

make sure you understand what you need to do. Once you understand it conceptually, coding it up is very

simple.

A <-> B <-> C and you want to insert D after B then the list would become A <-> B <-> D

<-> C. So that means that the previous item and next item pointers of both B and C will

need to change to accommodate the new item D.

Finding the head: The head of a list is a special item because it has no preceding

element (represented by a NULL pointer). Since all the elements in a list are connected,

finding the head merely requires traversing the list until a list item is found with no

preceding element. A function that finds the head of the list has one odd scenario; see if

you can figure out what it is.

Removing an element: Removing an element from a list is the opposite of adding to it.

Following the example above you’d go from a list like A <-> B <-> D <-> C to A <-> B <-> C.

The pointers of B and C both need to be modified to account for the removal of D.

Generally the data that was stored within D is also desired after the removal of the item

and should be returned.

malloc(), calloc(), and free()

This lab also relies on the use of memory allocation using malloc() (and/or calloc())

and free(). These are discussed somewhat in chapter 5 of K&R. As they are standard

library functions they are documented thoroughly online or in the Linux man-pages.

Refer to those resources to understand them.

It should be emphasized here that after any call to malloc() or calloc() you should

always check for NULL pointers! Memory allocation relies on the heap, which PlatformIO

specifies as 8192 bytes (0x200) for our Nucleo development kit by default. This project

requires at least a couple hundred bytes for malloc() and calloc() to work, so we can

proceed with the default heap size.

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4The linker script used by PlatformIO (which defines heap size) is auto-generated for all

supported chip architectures. You can find the location of the linker script for STM32

architectures under the “~/.platformio/packages/tool-ldscripts-ststm32/” path on

Linux/UNIX-like operating systems.

Note that this makes it easy to test that your code is properly checking for NULL

pointers: if you set the heap to 0, ALL calls to malloc()/calloc() will fail; if your code

doesn't crash, it's working!

Sorting

Sorting is an incredibly important function in computer programming. While you may

not think it is used a lot, it is quite common within a program to have the need to sort a

series of numbers. Sorting is an entire field of study within computer science and so

there are a huge number of algorithms that do just that. In this lab, you will be focusing

on two: Selection Sort is simple, intuitive, and easy to implement on a static array, but it

is slow. Insertion Sort is usually significantly faster, but it relies on a data structure that

allows insertion.

Selection sort partitions the list into two partitions. The first partition is sorted, while

the second partition is unsorted. At the start of the algorithm, the sorted partition is

empty. With each iteration, the sorted partition grows by one element, and the

unsorted partition shrinks, until there are no remaining unsorted items. This is achieved

by finding the smallest element in the unsorted partition and moving it to the sorted

partition.

Pseudo-code for selection sort is provided below. This pseudocode is written in a way

that makes it easy to apply to linkedLists, but note that in this case the pointers could

easily be replaced with indexes to a static array. We use two pointers: “FU” stands for

“First Unsorted”, representing the first item in the unsorted portion of the list. “S”

stands for “Scan”, since it “scans” through the unsorted partition, looking for the

smallest item.

FU is pointer to first item

while FU is not tail:

S is pointer to FU’s nextItem

while S is in list:

if FU > S:

swap FU and S contents

advance S

advance FU

The outer for loop effectively tracks the right-most element of the sorted array filling up

the left portion of the array. This means that for each iteration of the outer-loop, the

inner-loop can perform many element swaps.

Below is an example of Selection Sort in action:

D A C E B //

^FU ^S // D > A, swap and advance S

A D C E B //

^FU ^S // A < C, advance S

^FU ^S // A < E, advance S

^FU ^S // A < B, advance S

// S is at end of list, advance FU

A D C E B //

^FU ^S // D > C, swap and advance S

A C D E B //

^FU ^S // C < E, advance S

^FU ^S // C > B, swap and advance S

A B D E C //

// S is at end of list, advance FU

A B D E C //

^FU ^S // D < E, advance S

^FU ^S // D > C, swap and advance S

A B C E D //

// S is at end of list, advance FU

A B C E D //

^FU ^S // E > D, swap and advance S

A B C D E //

// S is at end of list, advance FU

// FU is at tail, return

Insertion Sort operates in a similar way to selection sort. Like Selection Sort, it partitions the list

into a sorted and unsorted portion, and uses a double-loop structure to move items from the

unsorted portion into the sorted portion. Unlike its slower cousin, insertion sort leverages an

“insert” operation to reduce the average time spent in the inner loop. Rather than “scanning”

through the unsorted partition in search of the smallest element, it scans through the sorted

portion to find the best place to insert the next item. It has the advantage that this scan does

not need to cover the entire sorted partition, instead stopping as soon as it finds the appropriate

place to insert.

Pseudocode for an insertion sort algorithm is given below. We use three pointers: “FS” stands

for “First Sorted”, and represents the first item in the sorted partition of the array. “LU” stands

for “Last Unsorted,” and represents the last item in the unsorted partition. Again “S” stands for

“scan,” since its job is to scan through the sorted partition to find the appropriate insertion

point.

FS = tail of list

while FS is not head of list:

LU = FS’s previous item

if LU < FS:

FS = LU

else:

S = FS

while (S is not tail of list):

if S's next item is greater than LU:

break

else:

S = S's next item

remove LU item

re-insert after S

Insertion Sort is slower than Selection Sort in a static array, but can be very quick in a linked list

data structure.

Note that LinkedList.h does not have a true “insert” function. You can achieve something similar

by removing an item and then using CreateAfter() or CreateBefore() to insert it back in

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. You will

also need to account for inserting items at the beginning and end of your list.

Below, you can see the InsertionSort in action:

5 Don’t forget to save the pointer to the ListItem’s data member before you remove!

D A C E B //

^LU ^FS // E > B, make an S pointer

^S // B < E, advance S

// S is at end of list, insert

D A C B E //

^LU ^FS // C > B, make an S pointer

^S // C < E, insert

D A B C E //

^LU ^FS // A < B, advance FS and LU

D A B C E //

^LU ^FS // D > A, make S pointer

^S // D > B, advance S

^S // D > C, advance S

^S // D < E, insert

A B C D E // FS is head, return

^FS

You will write code for both of these algorithms inside of the SelectionSort() and InsertionSort()

functions in sort.c.

Evaluating SelectionSort() and InsertionSort() in Lab06_main.c

Although we have stated that InsertionSort() is faster than SelectionSort(), we should

test that claim experimentally. To do this, we will use the “stopwatch” library [included

in this assignment’s directory] to start, stop, and report the differences between their

execution times.

To measure the time required to execute SelectionSort(), we need to track the system

time immedIately before and after SelectionSort(), and then run our code. To do this

using the stopwatch.c library included with this lab:

1. Stopwatch_Init() – This function sets up your system’s clock; only needs to be

called once.

2. Stopwatch_StartBenchmark() – Starts or restarts the stopwatch timer.

3. Stopwatch_StopBenchmark() – Stops the stopwatch timer and saves the results

in its local scope.

4. Stopwatch_PrintBenchmarkResults() – Displays information about the cycles

required/time past for the last benchmark run. NOTE: You will need to call this

function to see the results after running “Stopwatch_StopBenchmark()”!

Approaching this lab

Like all labs for this class, you should first start with implementing the LinkedList library.

Be sure to handle when malloc() returns NULL, NULL pointers as arguments to functions,

and whether the function expects the head of the list or not.

1. Implement LinkedListNew().

Test this by writing code to create a new list of size 1. Manually inspect the

resultant struct that is created using the Variables window in VS

Code/PlatformIO to see that it is correct while running on your Nucleo.

2. Implement LinkedListCreateAfter() and LinkedListCreateBefore().

Test these by creating a list of multiple sizes greater than 1. Manually inspect the

resultant list using the Variables window in VS Code/PlatformIO.

3. Now that you can create lists of a multitude of sizes, implement

LinkedListGetFirst(). This function will be helpful for implementing the other

functions.

Test this function by creating a few different lists, storing the pointer to the head

node. Pass a non-head node to GetFirst() and see if it matches the memory

address of the head node.

4. Implement LinkedListGetSize().

Run it on the different size lists you created earlier and confirm that results are

as expected.

5. Implement LinkedListPrint() and LinkedListSwapData().

These should be straight-forward to test.

6. At this point you are now ready for implementing SelectionSort() and

InsertionSort in sort.c. The debugger will be very useful here. You may find it

convenient to use a shorter list during testing.

7. Once SelectionSort() and InsertionSort() are functional, use the stopwatch tool

and the debugger to measure the time required for each sort. Record the

results in README.pdf and explain them.

A note on using GNUmakefile

One beautiful perk of using Makefiles is easy cleanup. While in the previous lab, you had to

remove every object (.o) file and executable individually, the GNUmakefile provided for you in

this lab assignment can take care of this mess for you. Simply type into your terminal:

Unset

$ make clean

This is just one of many useful features that you can reap from having a well-built Makefile,

especially when dealing with larger projects. We encourage you to read more about building

Makefiles.

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A note on testing with PlatformIO/VS Code

While Makefiles (e.g. GNUmakefile) allow you to specify the target that you would like to

compile and run on your microcontroller, for the purposes of our course you will only be able to

build a PlatformIO project with one “main()” function declared within its scope. For example in

this lab assignment, you will need to move either your LinkedListTest.c or your Lab06_main.c to a

directory outside of the “src/” directory of your project for it to compile. We suggest leaving any

files that you do not want to build in your “Lab06/” directory for safe-keeping, then swapping

them between there and the “Lab06/src/” directory depending on which main() function you

would like to run.

How your code will be tested

Like previous labs, your code will be tested using your code as a library where we will

test with different programs to exercise your library on both Nucleo and Linux. Your

LinkedListTest.c program will also be run so that we can observe your testing output.

6 A thorough (but perhaps overwhelming) guide to writing Makefiles is the GNU Make manual. This guide

contains a comprehensive description of the features offered by Makefiles, and it is not terribly-written;

however, it is very long. A more practical approach, as with much software development, is to read and

analyze other developers’ code when you encounter it (key word: “analyze”).