Description

In this programming assignment, you will implement smart arrays (arrays that expand automatically whenever they get too full). This is an immensely powerful and awesome data structure, and it will ameliorate several problems we often encounter with arrays in C (see pg. 3 of this PDF).

By completing this assignment, you will gain advanced experience working with dynamic memory management and structs in C. You will also gain additional experience managing programs that use multiple source files. In the end, you will have an awesome and useful data structure that you can reuse in the future.

Attachments

SmartArray.h, testcase{01-05}.c, output{01-05}.txt, names.txt, SmartArray-diagram.pdf, and test-all.sh

Deliverables

SmartArray.c

(Note! Capitalization and spelling of your filename matters!)

1. Overview

A smart array is an array that grows to accommodate new elements whenever it gets too full. As with normal arrays in C, we have direct access to any index of the smart array at any given time. There are four main advantages to using smart arrays, though:

1. We do not need to specify the length of a smart array when it is created. Instead, it will automatically expand when it gets full. This is great when we don’t know ahead of time just how much data we’re going to end up holding in the array.
2. We will use get() and put() functions to access individual elements of the array, and these functions will check to make sure we aren’t accessing array positions that are out of bounds. (Recall that C doesn’t check whether an array index is out of bounds before accessing it during program execution. That can lead to all kinds of whacky trouble!)
3. If our arrays end up having wasted space (i.e., they aren’t full), we can trim them down to size.
4. In C, if we have to pass an array to a function, we also typically find ourselves passing its length to that function as a second parameter. With smart arrays, the length will get passed automatically with the array, as they’ll both be packaged together in a struct.

While some languages offer built-in support for smart arrays (such as Java’s ArrayList class), C does not. That’s where you come in. You will implement basic smart array functionality in C, including:

1. automatically expanding the smart array’s capacity when it gets full;
2. adding new elements into arbitrary positions in the smart array, or at the end of the smart array;
3. providing safe access to elements at specific positions in the smart array;
4. gracefully signaling to the user (i.e., the programmer (re-)using your code) when he or she attempts to access an index in the smart array that is out of bounds (instead of just segfaulting);
5. … and more!

In this assignment, your smart array will be designed to hold arrays of strings. A complete list of the functions you must implement, including their functional prototypes, is given below in Section 3, “Function Requirements”). You will submit a single source file, named SmartArray.c, that contains all required function definitions, as well as any auxiliary functions you deem necessary. In SmartArray.c, you should #include any header files necessary for your functions to work, including SmartArray.h (see Section 2, “SmartArray.h”).

Note that you will not write a main() function in the source file you submit! Rather, we will compile your source file with our own main() function(s) in order to test your code. We have attached example source files that have main() functions, which you can use to test your code. We realize this is completely new territory for most of you, so don’t panic. We’ve included instructions on compiling multiple source files into a single executable (e.g., mixing your SmartArray.c with our SmartArray.h and testcase01.c) in Sections 4 and 5 (“Compilation and Testing”).

Although we have included sample main() functions to get you started with testing the functionality of your code, we encourage you to develop your own test cases, as well. Ours are by no means comprehensive. We will use much more elaborate test cases when grading your submission.

Start early. Work hard. Good luck!

2. SmartArray.h

This header file contains the struct definition and functional prototypes for the smart array functions you will be implementing. You should #include this file from your SmartArray.c file, like so:

 

#include “SmartArray.h”

Recall that the “quotes” (as opposed to <brackets>) indicate to the compiler that this header file is found in the same directory as your source, not a system directory.

You should not modify SmartArray.h in any way, and you should not send SmartArray.h when you submit your assignment. We will use our own unmodified copy of SmartArray.h when compiling your program.

If you write auxiliary functions in SmartArray.c (which is strongly encouraged!), you should not add those functional prototypes to SmartArray.h. Just put those functional prototypes at the top of your SmartArray.c.

Think of SmartArray.h as a public interface to the SmartArray data structure. It contains only the functions that the end user (i.e., the programmer (re-)using your code) should call in order to create and use a SmartArray. You do not want the end user to call your auxiliary functions directly, so you do not put those functional prototypes in SmartArray.h. That way, the end user doesn’t need to worry about all your auxiliary functions in order to use an SmartArray; everything just works. (And you don’t have to worry about the end user mucking everything up by accidentally calling auxiliary functions that he or she shouldn’t be messing around with!)

The basic struct you will use to implement the smart arrays (defined in SmartArray.h) is as follows:

 

 

typedef struct SmartArray

{

char **array;   // pointer to array of strings    int size;       // number of elements in array    int capacity;   // length of array (maximum capacity) } SmartArray;

 

 

The SmartArray struct contains a double char pointer that can be used to set up a 2D char array (which is just an array of char arrays, otherwise known as an array of strings). array will have to be allocated dynamically at runtime. It will probably be the bane of your existence for the next week or so.

The struct also has size and capacity variables, which store the number of elements in the array (initially zero) and the current length (i.e., maximum capacity) of the array, respectively.

3. Function Requirements

In the source file you submit, SmartArray.c, you must implement the following functions. You may implement any auxiliary functions you need to make these work, as well. Please be sure the spelling, capitalization, and return types of your functions match these prototypes exactly. In this section, I often refer to malloc(), but you’re welcome to use calloc() or realloc() instead, as you see fit.

SmartArray *createSmartArray(int length);

Description: Dynamically allocate space for a new SmartArray. Initialize its internal array to be of length length or DEFAULT_INIT_LEN, whichever is greater. (DEFAULT_INIT_LEN is defined in SmartArray.h.) Properly initialize pointers in the array to NULL, and set the size and capacity members of the struct to the appropriate values.

Output: “-> Created new SmartArray of size <N>.” (Output should not include the quotes. Terminate the line with a newline character, ‘\n’. <N> should of course be the length of the new array, without the angled brackets.)

Returns: A pointer to the new SmartArray, or NULL if any calls to malloc() failed.

SmartArray *destroySmartArray(SmartArray *smarty);

Description: Free any dynamically allocated memory associated with the SmartArray struct and return NULL.

Returns: NULL pointer.

SmartArray *expandSmartArray(SmartArray *smarty, int length);

Description: Dynamically allocate a new array of length length. Copy the contents of smarty’s old array into the new array. Free any memory associated with the old smarty→array that is no longer in use, then set smarty→array to point to the newly created array. Be sure all pointers are properly initialized. Update the size and capacity of the SmartArray (if applicable).

Note: If length is less than or equal to smarty’s current array capacity, or if the smarty pointer is NULL, you should NOT modify the SmartArray at all. In that case, just return from the function right away without producing any output.

Output: “-> Expanded SmartArray to size <N>.” (Output should not include the quotes. Terminate the line with a newline character, ‘\n’. <N> should be the new length of the array, without the angled brackets. Do NOT produce any output if you the array is not expanded.)

Returns: A pointer to the SmartArray, or NULL if any calls to malloc() failed.

SmartArray *trimSmartArray(SmartArray *smarty);

Description: If smarty’s capacity is greater than its current size, trim the length of the array to the current size. You will probably want to malloc() a new array to achieve this. If so, avoid memory leaks as you get rid of the old array. Update any members of smarty that need to be updated as a result of this action.

Output: “-> Trimmed SmartArray to size <N>.” (Output should not include the quotes. Terminate the line with a newline character, ‘\n’. <N> should be the new length of the array, without the angled brackets. Do NOT produce any output if the length of the array is not reduced by this function.) Returns: A pointer to the SmartArray, or NULL if malloc() failed or if smarty was NULL.

 

 

char *put(SmartArray *smarty, char *str);

Description: Insert a copy of str into the next unused cell of the array. If the array is already full, call expandSmartArray() to grow the array to length (capacity * 2 + 1) before inserting the new element.  When copying str into the array, only allocate the minimum amount of space necessary to store the string.

Returns: A pointer to the copy of the new string that was inserted into the array, or NULL if the string could not be added to the array (e.g., malloc() failed, or smarty or str was NULL).

 

 

char *get(SmartArray *smarty, int index);

Description: Attempts to return the element at the specified index. This is where you protect the user from going out-of-bounds with the array.

Returns: A pointer to the string at position index of the array, or NULL if index was out of bounds or the smarty pointer was NULL.

 

 

char *set(SmartArray *smarty, int index, char *str);

Description: If the array already has a valid string at position index, replace it with a copy of str. Otherwise, the operation fails and we simply return NULL. Ensure that no more space is used to store the new copy of str than is absolutely necessary (so, you might have to use malloc() and free() here).

Returns: A pointer to the copy of the string placed in the SmartArray, or NULL if the operation failed for any reason (e.g., invalid index, or smarty or str was NULL).

 

 

char *insertElement(SmartArray *smarty, int index, char *str);

Description: Insert a copy of str at the specified index in the array. Any elements to the right of index are shifted one space to the right. If the specified index is greater than the array’s size, the element being inserted should be placed in the first empty position in the array. (Continued from previous page…) As with the put() function, if the SmartArray is already full, call expandSmartArray() to grow the array to length (capacity * 2 + 1) before inserting the new element.  When copying str into the array, only allocate the minimum amount of space necessary to store the string.

Returns: A pointer to the copy of the string inserted into the array, or NULL if insertion fails for any reason (e.g., malloc() failed, or smarty or str was NULL).

 

 

int removeElement(SmartArray *smarty, int index);

Description: Remove the string at the specified index in the array. Strings to the right of index are shifted one space to the left, so as not to leave a gap in the array. The SmartArray’s size member should be updated accordingly. If index exceeds the SmartArray’s size, nothing is removed from the array.

Returns: 1 if an element was successfully removed from the array, 0 otherwise (including the case where the smarty pointer is NULL).

 

 

int getSize(SmartArray *smarty);

Description: This function returns the number of elements currently in the array. We provide this function to discourage the programmer from accessing smarty→size directly. That way, if we decide to change the name or meaning of the size variable in our SmartArray struct, the programmers who download the latest version of our code can get it working right out of the box; they don’t have to go through their own code and change all instances of smarty→size to something else, as long as we provide them with a getSize() function that works. Returns: Number of elements currently in the array, or -1 if the smarty pointer is NULL.

 

 

void printSmartArray(SmartArray *smarty);

Description: Print all strings currently in the array.

Output: Print all strings currently in the array. Print a newline character, ‘\n’, after each string. If the SmartArray pointer is NULL, or if the array is empty, simply print “(empty array)” (without quotes), followed by a newline character, ‘\n’.

 

 

double difficultyRating(void);

Returns: A double indicating how difficult you found this assignment on a scale of 1.0 (ridiculously easy) through 5.0 (insanely difficult).

 

 

double hoursSpent(void);

Returns: An estimate (greater than zero) of the number of hours you spent on this assignment.

 

Compilation and Testing (CodeBlocks)

The key to getting a multiple files to compile into a single program in CodeBlocks (or any IDE) is to create a project. Here are the step-by-step instructions for creating a project in CodeBlocks, importing SmartArray.h, testcase01.c, and the SmartArray.c file you’ve created (even if it’s just an empty file so far).

1. Start CodeBlocks.
2. Create a New Project (File -> New -> Project).
3. Choose “Empty Project” and click “Go.”
4. In the Project Wizard that opens, click “Next.”
5. Input a title for your project (e.g., “SmartArray”).
6. Choose a folder (e.g., Desktop) where CodeBlocks can create a subdirectory for the project.
7. Click “Finish.”

Now you need to import your files. You have two options:

1. Drag your source and header files into CodeBlocks. Then right click the tab for each file and choose “Add file to active project.”

– or –

2. Go to Project -> Add Files…. Browse to the directory with the source and header files you want to import. Select the files from the list (using CTRL-click to select multiple files). Click “Open.” In the dialog box that pops up, click “OK.”

You should now be good to go. Try to build and run the project (F9).

Note that if you import both testcase01.c and testcase02.c, the compiler will complain that you have multiple definitions for main(). You can only have one of those in there at a time. You’ll have to swap them out as you test your code.

Yes, constantly swapping out the test cases in your project will be a bit annoying. You can avoid this if you’re willing to migrate away from an IDE and start compiling at the command line instead. If you’re interested in doing that in Windows, please look around online for instructions on how to make that happen, and see a TA in office hours if you get stuck. Alternatively, you might consider installing Linux on a separate partition of your hard drive. If you take that approach, just be sure to back up your hard drive first.

Note! Even if you develop your code with CodeBlocks on Windows, you ultimately have to transfer it to the Eustis server to compile and test it there. See the following page (Section 5, “Compilation and Testing (Linux/Mac Command Line)”) for instructions on command line compilation in Linux.

Compilation and Testing (Linux/Mac Command Line)

To compile multiple source files (.c files) at the command line:

gcc SmartArray.c testcase01.c

By default, this will produce an executable file called a.out, which you can run by typing:

./a.out

If you want to name the executable file something else, use:

gcc SmartArray.c testcase01.c -o SmartArray.exe

…and then run the program using:

./SmartArray.exe

Running the program could potentially dump a lot of output to the screen. If you want to redirect your output to a text file in Linux, it’s easy. Just run the program using the following command, which will create a file called whatever.txt that contains the output from your program:

./SmartArray.exe > whatever.txt

Linux has a helpful command called diff for comparing the contents of two files, which is really helpful here since we’ve provided several sample output files. You can see whether your output matches ours exactly by typing, e.g.:

diff whatever.txt output01.txt

If the contents of whatever.txt and output01.txt are exactly the same, diff won’t have any output. It will just look like this:

seansz@eustis:~$ diff whatever.txt output01.txt seansz@eustis:~$ _

If the files differ, it will spit out some information about the lines that aren’t the same. For example:

seansz@eustis:~$ diff whatever.txt output01.txt

6c6

< Size of array: 0

—

> Size of array: -1

seansz@eustis:~$ _

Getting Started: A Guide for the Overwhelmed

Okay, so, this might all be overwhelming, and you might be thinking, “Where do I even start with this assignment?! I’m in way over my head!”

Don’t panic! We’re here to help in office hours, and here’s my general advice on starting the assignment (as well as a few hints and spoilers):

1. First and foremost, start working on this assignment early. Nothing will be more frustrating than running into unexpected errors or not being able to figure out what the assignment is asking you to do on the day that it is due.
2. Start by creating a skeleton c file. Add a header comment, add some standard #include directives, and be sure to include SmartArray.h from your source file. Then copy and paste each functional prototype from SmartArray.h into SmartArray.c, and set up all those functions return dummy values (zero, NULL, etc.). For example:

#include <stdio.h> #include <stdlib.h> #include “SmartArray.h” SmartArray *createSmartArray(int length) { return NULL; } int getSize(SmartArray *smarty) { return 0; } // …and so on.

3. Test that your c source file compiles. If you’re at the command line on a Mac or in Linux, your source file will need to be in the same directory as SmartArray.h, and you can test compilation like so:

gcc -c SmartArray.c

Alternatively, you can try compiling it with one of the test case source files, like so:

gcc SmartArray.c testcase01.c

For more details, see Section 5, “Compilation and Testing (Linux/Mac Command Line).”

 

If you’re using an IDE (i.e., you’re coding with something other than a plain text editor and the command line), open up your IDE and start a project using the instructions above in Section 4, “Compilation and Testing (CodeBlocks)”. Import SmartArray.h, testcase01.c, and your new SmartArray.c source file, and get the program compiling and running before you move forward. (Note that CodeBlocks is the only IDE we officially support in this class.)

4. Once you have your project compiling, go back to the list of required functions (Section 3, “Function Requirements”), and try to implement one function at a time. Always stop to compile and test your code before moving on to another function!
5. You’ll probably want to start with the createSmartArray() (Alternatively, printSmartArray() might be a good starting point, as well.)

As you work on createSmartArray(), write your own main() function that calls createSmartArray() and then checks the results. For example, you’ll want to ensure that createSmartArray() is returning a non-NULL pointer to begin with, and that the fields inside the SmartArray struct that it created are properly initialized when you examine them back in main(). If you’re uncertain about how to call certain functions, read through my sample main files for examples.

6. After writing createSmartArray(), I would probably work on the printSmartArray() function, because it will be immensely useful in debugging your code as you work. Here’s how I’d test these functions at first: In your own main() function, call createSmartArray(). Then, back in main(), manually insert one or two strings into the smart array before passing it to the printSmartArray() Make sure everything works as intended and the output is as expected. If not, trace carefully through your code to see what went wrong.
7. If you get stuck, draw diagrams. Make boxes for all the variables in your program. If you’re dynamically allocating memory, diagram them out and make up addresses for all your variables. Trace through your code carefully using these diagrams.
8. With so many pointers, you’re bound to encounter errors in your code at some point. Use printf() statements liberally to verify that your code is producing the results you think it should be producing (rather than making assumptions that certain components are working as intended). You should get in the habit of being immensely skeptical of your own code and using printf() to provide yourself with evidence that your code does what you think it does.
9. When looking for a segmentation fault, you should always be able to use printf() and fflush() to track down the exact line you’re crashing on.
10. You’ll need to examine a lot of debugging output. You might want to set up a function that prints debugging strings only when you #define a DEBUG value to be something other than zero, so you can easily flip debugging output on and off. (Just be sure to remove your debugging statements before you submit your assignment, so your code is nice and clean and easy for us to read.)

7. Troubleshooting: File Not Found Errors with Mac OS X

If you encounter a file-not-found error on your Mac, you might need to put your input files in an unusual directory. Use my pwd() (“print working directory”) function to print the directory where your IDE wants you to put those input files. pwd() is defined in file-read.c, posted Jan. 23 in Webcourses.

8. Test Cases and the test-all.sh Script

We’ve included multiple test cases with this assignment, which show some ways in which we might test your code. These test cases are not comprehensive. You should also create your own test cases if you want to test your code comprehensively. In creating your own test cases, you should always ask yourself, “How could these functions be called in ways that don’t violate the program specification, but which haven’t already been covered in the test cases included with the assignment?”

We’ve also included a script, test-all.sh, that will compile and run all test cases for you. You can run it on Eustis by placing it in a directory with SmartArray.c, SmartArray.h, and all the test case files, and typing:

bash test-all.sh

9. Deliverables

Submit a single source file, named SmartArray.c, via Webcourses. The source file should contain definitions for all the required functions (listed above), as well as any auxiliary functions you need to make them work.

Your source file must not contain a main() function. Do not submit additional source files, and do not submit a modified SmartArray.h header file. Your source file (without a main() function) should compile at the command line using the following command:

gcc -c SmartArray.c

It must also compile at the command line if you place it in a directory with SmartArray.h and a test case file (for example, testcase01.c) and compile like so:

gcc SmartArray.c testcase01.c

Be sure to include your name and NID as a comment at the top of your source file.

Continued on the following page…