ListyString and ListyNode Structs (ListyString.h)

For your linked lists, you must use the structs we have specified in ListyString.h without any modifications. You must #include the header file from ListyString.c like so:

#include "ListyString.h"

The node struct you will use for your linked lists is defined in ListyString.h as follows:

typedef struct ListyNode {

char data; // Each node holds a single character.

struct ListyNode *next; // Pointer to next node in linked list.

} ListyNode;

Additionally, there is a ListyString struct that you will use to store the head of each linked list string, along with the length of that list:

typedef struct ListyString {

struct ListyNode *head; // Pointer to head of string's linked list.

int length; // Length of this string / linked list.

} ListyString;

Capturing Command Line Arguments in a C Program In this assignment, you will have to open and process an input file. When we run your program, we will use a command line argument to specify the name of the input file that your program will read. We will always give the name of a valid input file as a command line argument when running your program. For example:

./a.out input01.txt

Its super easy to get command line arguments (like the string input01.txt in this example) into your program. You just have to change the function signature for main(). Whereas we have typically seen main() defined using int main(void), you will now use the following function signature instead:

int main(int argc, char **argv)

Within main(), argc is now an integer representing the number of command line arguments passed to the program (including the name of the executable itself). argv is an array of strings that stores all those command line arguments. argv[0] stores the name of the program being executed.

Input Files One of the required functions for this program needs to open and process an input file. The first line of the input file will always be a single string that contains at least 1 character and no more than 1023 characters, and no spaces. The first thing you should do when processing an input file is to read in that string and convert it to a ListyString (i.e., a linked list string). That will become your working string, and you will manipulate it according to the remaining commands in the input file. Each of the remaining lines in the file will correspond to one of the following string manipulation commands, which you will apply to your working string in order to achieve the desired output for your program:

COMMAND	DESCRIPTION
@ key str	In your working string, replace all instances of key with str.
+ str	Concatenate str to the end of your working string
- key	Delete all instances of key (if any) from your working string.
~	Reverse the working string.
?	Print the number of characters in the working string.
!	Print the working string.

Important note: For the first three commands listed in this table, key is always a single character, and str is a string. Both key and str are guaranteed to contain alphanumeric characters only (A-Z, a-z, and 0-9). Not counting the need for a null terminator (\0), str can range from 1 to 1023 characters (inclusively). So, with the null terminator, you might need up to 1024 characters to store str as a char array when reading from the input file.

Another important note: If one of the above commands modifies your working string, you should also ensure that the length member of that ListyString struct gets updated.

Function Requirements

int main(int argc, char **argv); Description: You have to write a main() function for this program. It should only do the following three things: (1) capture the name of an input file (passed as a command line argument), (2) call the processInputFile() function (passing it the name of the input file to be processed), and (3) return zero. Returns: 0 (zero).

int processInputFile(char *filename); Description: Read and process the input file (whose name is specified by the string filename) according to the description above in Section 3, Input Files. To perform the string manipulations described in that section, you should call the corresponding required functions listed below. In the event that a bad filename is passed to this function (i.e., the specified file does not exist), this function should simply return 1 without producing any output. Output: This function should only produce output if the input file has ? and/or ! commands. For details, see Section 3 (Input Files), or refer to the input/output files included with this assignment. Note that this function should not produce any output if the input file does not exist. Returns: If the specified input file does not exist, return 1. Otherwise, return 0.

ListyString *createListyString(char *str); Description: Convert str to a ListyString by first dynamically allocating a new ListyString struct, and then converting str to a linked list string whose head node will be stored inside that ListyString struct. Be sure to update the length member of your new ListyString, as well. Special Considerations: str may contain any number of characters, and it may contain nonalphanumeric characters. If str is NULL or an empty string (), simply return a new ListyString whose head is initialized to NULL and whose length is initialized to zero. Runtime Requirement: This should be an O(k) function, where k is the length of str. Returns: A pointer to the new ListyString. Ideally, this function would return NULL if any calls to malloc() failed, but I do not intend to test your code in an environment where malloc() would fail, so you are not required to check whether malloc() returns NULL.

ListyString *destroyListyString(ListyString *listy); Description: Free any dynamically allocated memory associated with the ListyString and return NULL. Be sure to avoid segmentation faults in the event that listy or listy->head are NULL. Returns: NULL.

ListyString *cloneListyString(ListyString *listy); Description: Using dynamic memory allocation, create and return a new copy of listy. Note that you should create an entirely new copy of the linked list contained within listy. (That is, you should not just set your new ListyStrings head pointer equal to listyhead.) The exception here is that if listy->head is equal to NULL, you should indeed create a new ListyStruct whose head member is initialized to NULL and whose length member is initialized to zero. If listy is NULL, this function should simply return NULL. Runtime Requirement: The runtime of this function should be no worse than O(n), where n is the length of the ListyString. Returns: A pointer to the new ListyString. If the listy pointer passed to this function is NULL, simply return NULL.

void replaceChar(ListyString *listy, char key, char *str); Description: This function takes a ListyString (listy) and replaces all instances of a certain character (key) with the specified string (str). If str is NULL or the empty string (), this function simply removes all instances of key from the linked list. If key does not occur anywhere in the linked list, the list remains unchanged. If listy is NULL, or if listy->head is NULL, simply return. Important Note: Be sure to update the length member of the ListyString as appropriate. Runtime Requirement: The runtime of this function should be no worse than O(n + km), where n is the length of the ListyString, k is the number of times key occurs in the ListyString, and m is the length of str. Returns: Nothing. This is a void function.

void reverseListyString(ListyString *listy); Description: Reverse the linked list contained within listy. Be careful to guard against segfaults in the cases where listy is NULL or listy->head is NULL. Runtime Consideration: Ideally, this function should be O(n), where n is the length of the ListyString. Note that if you repeatedly remove the head of listys linked list and insert it at the tail of a new linked list using a slow tail insertion function, that could devolve into an O(n2) approach to solving this problem. Returns: Nothing. This is a void function.

ListyString *listyCat(ListyString *listy, char *str); Description: Concatenate str to the end of the linked list string inside listy. If str is either NULL or the empty string (), then listy should remain unchanged. Be sure to update the length member of listy as appropriate. Special Considerations: If listy is NULL and str is a non-empty string, then this function should create a new ListyString that represents the string str. If listy is NULL and str is NULL, this function should simply return NULL. If listy is NULL and str is a non-NULL empty string (), then this function should return a ListyString whose head member has been initialized to NULL and whose length member has been initialized to zero. Runtime Requirement: The runtime of this function must be no worse than O(n+m), where n is the length of listy and m is the length of str. Returns: If this function caused the creation of a new ListyString, return a pointer to that new ListyString. If one of the special considerations above requires that a NULL pointer be returned, then do so. Otherwise, return listy.

int listyCmp(ListyString *listy1, ListyString *listy2); Description: Compare the two ListyStrings. Return 0 (zero) if they represent equivalent strings. Otherwise, return any non-zero integer of your choosing. Note that the following are not considered equivalent: (1) a NULL ListyString pointer and (2) a non-NULL ListyString pointer in which the head member is set to NULL (or, equivalently, the length member is set to zero). For the purposes of this particular function, (2) represents an empty string, but (1) does not. Two NULL pointers are considered equivalent, and two empty strings are considered equivalent, but a NULL pointer is not equivalent to an empty string. Runtime Requirement: The runtime of this function must be no worse than O(n+m), where n is the length of listy1 and m is the length of listy2. Returns: 0 (zero) if the ListyStrings represent equivalent strings; otherwise, return any integer other than zero.

int listyLength(ListyString *listy); Description: Return the length of the ListyString (i.e., the length of listys linked list). Runtime Requirement: The runtime of this function must be O(1). Returns: The length of the string (i.e., the length of the linked list contained within listy). If listy is NULL, return -1. If listy is non-NULL, but listy->head is NULL, return zero.

void printListyString(ListyString *listy); Description: Print the string stored in listy, followed by a newline character, . If listy is NULL, or if listy represents an empty string, simply print (empty string) (without the quotes), follow by a newline character, . Returns: Nothing. This is a void function.