1. Follow the following development steps, in order—and submit after every step. You may submit more often, but be sure to have at least one submission for each step below. You cannot go back. There will be a penalty if you do not follow this.
   1. Set up your project as described in Getting started (above). Modify split_string.h with the required struct type definitions (described in the table below). Make sure everything compiles and your tests for copy_substring(…) still pass. Submit
   2. Add or update a test for the append_substring(…) function to add a single string to an empty Strings object (i.e., a Strings object that refers to an empty list). Implement just enough to add a single node to an empty list. At this point, it is okay if your code has a memory leak.
      ⚠ Do not implement the entire append function, yet.
      Submit
   3. Add or update a test for the append_substring(…) function to add a string to a non-empty Strings object (i.e., a Strings object that refers to a linked list with at least one node). Implement the rest of the append_substring(…) function, so that it can append to any Strings object (i.e., empty or non-empty). At this point, it is okay if your code has a memory leak. Submit
   4. Add or update a test for free_strings(…) to free a Strings object with one string (i.e., one node in the linked list). Implement just enough in split_string.c to make your new test pass, i.e., to free a Strings object referring to a list with one node.
      ⚠ Do not implement free_strings(…) for lists with multiple strings, yet.
      Submit
   5. Add or update a test for find_substring(…) in test_split_string.c. Implement just enough in split_string.c to make that test pass. Submit
   6. Add or update a test for split_string(…) in test_split_string.c. Implement just enough in split_string.c to make that test pass. Submit
   You will need to add other stuff, too. For example, there is no step written above for freeing a list of size ≥ 2 but obviously, you will need that.
2. Your submission must contain each of the following files, as specified:

   file	contents
   split_string.h	struct types	Node Define a struct type called Node with two fields: .next (Node*) and .string (char*).
   		Strings Define a struct type called struct Strings with two three fields: .strings (char**) .head (Node*), .tail (Node*), and .num_strings (size_t).
   		FindResult Define a struct type called struct FindResult with two fields: .needle (char const*) and .idx (size_t).
   	function declarations	The bottom of the file contains declarations for the functions that are required for split_string.c. Do not modify those declarations (unless directed in writing by the instructor).
   split_string.c	function definitions	find substring(char const✶✶ a pos, Strings needles) → return type: struct FindResult Find the first occurrence of any of the strings in needles within the string beginning at *a_pos. a_pos is the address of a char* indicating where to begin searching. If we call the full string being searched the haystack, *a_pos could be the beginning of the haystack or some address in the middle—wherever we want to begin searching. If at least one of the needles is found within the string at *a_pos… Return a struct FindResult object of which the .idx field indicates the index within the string at *a_pos where the first needle was found, and the .needle is one of the strings within needles. Set *a_pos to the address of the character immediately after the first needle found. In case an of the needles overlap, the one with the earlier index takes priority. For example, when searching "abcdefghi" for the needles {"cde", "cd", "hi"}, the .needle field of the returned object would be "cde" because it comes first in the array of needles. find_substring(…) must not result in any calls to malloc(…). If none of the needles is found… Return a struct FindResult object of which the .idx field is 0 and the .needle field is NULL. Do not modify *a_pos. This is a support function. It is included in this assignment to guide you in implementing split_string(…), though it could certainly be useful on its own. ⇆ compared to HW09): requirements are the same. body will be a little different. With instructor's solution, 3 lines were removed and 3 lines added (i.e., same total length).
   		copy substring(char const✶ src string, size t substring len) → return type: char✶ Create a string on the heap containing the first (up to) substring_len characters from src_string. Each call to copy_substring(…) should result in one call to malloc(…). Caller is responsible for freeing the heap memory buffer allocated by this function. ⚠ Do not call free(…) in this function. ⇆ Compared to HW09): No changes.
   		append substring(char const✶ string, size t max string len, Strings✶ a strings) Append a new node to the linked list referred to by *a_strings. The .string field of the new node should refer to a newly allocated string on the heap containing the first (up to) max_string_len characters from string. You can (and should) call copy_substring(…) from append_substring(…). Calling append_substring(…) should result in two (2) calls to malloc(…). Caller is responsible for freeing the heap memory buffer allocated by this function. ⚠ Do not call free(…) in this function. ⇆ Compared to HW09): This function is new. Body of instructor's solution is 10 sloc (source lines of code). Yours may be longer.
   		free strings(Strings✶ a strings) Free all memory referred to (directly or indirectly) by *a_strings. The purpose of free_strings(…) is to free the result that will be returned by split_string(…). This must free each of the strings (i.e., (*a_strings).strings[0], etc.) as well as the outer array (i.e., (*a_strings).strings). Calling free_strings(…) should not result in any calls to malloc(…) ⇆ Compared to HW09): Requirements are the same. Body will be completely different. Instructor's solution is 7 sloc (source lines of code). Yours may be longer.
   		split string(char const✶ text, Strings delimiters) → return type: Strings Split the string text by each non-overlapping occurrence of any of the strings in delimiters. Return a linked list of strings (as a Strings object), an array of strings (char*) on the heap, including the delimiters. Each string in the linked list this array (including the delimiters) should be newly created (malloc'd). Each call to split_string(…) should result in 2n n + 1 calls to malloc, where n is the number of parts in the resulting array. There will be one call to malloc(…) for the string and one call to malloc(…) for the linked list node. The Strings object itself will be on the stack. You know it has to be on the stack because this returns a Strings object (not a Strings*). In case a delimiter falls at the beginning or end of text, and/or consecutive occurrences of delimiters, the returned array will contain one or more empty strings. Caller is responsible for freeing the heap memory buffer allocated by this function. ⚠ Do not call free(…) in this function. ⇆ Compared to HW09): Requirements are the same. Body will be a little different. With instructor's solution, 5 lines (out of 13) were removed, and 5 lines added (i.e., same total length).
   test_split_string.c	functions	main(int argc, char✶ argv[]) → return type: int Test the code in your split_string.c using your miniunit.h. 100% code coverage is required for split_string.c.
   		test ▒▒▒() → return type: int Use your mu_check_strings_equal(…) from HW06 to check that the code in your split_string.c is working correctly.
   		test ▒▒▒() → return type: int
   		test ▒▒▒() → return type: int
   miniunit.h	macros	Same as HW06. Okay to modify, if you wish.
   log_macros.h	macros	Same as HW05. Okay to modify, if you wish.
   Makefile	macros	Same as HW07. Okay to modify, if you wish.

3. ⚠ Do not use typecasts anywhere in HW10. The code quality standard says typecasts may not be used, except when they are truly necessary, safe, and you can articulate why. They are not necessary for anything in HW10.
4. Only the following external header files, functions, and symbols are allowed in split_string.c.

   header	functions/symbols	allowed in…
   stdbool.h	bool, true, false	*
   stdio.h	*	test_split_string.c
   assert.h	assert	*
   stdlib.h	EXIT_SUCCESS	test_split_string.c
   stdlib.h	malloc, free	*
   string.h	strlen, strcpy, strncpy, strcmp, strstr, strncmp, memcpy, memmove	*

   All others are prohibited unless approved by the instructor. Feel free to ask if there is something you would like to use.
5. ⚠ Do not use strtok(…) (function from C standard libary).
6. Submissions must meet the code quality standards and the policies on homework and academic integrity.

Pre-tester ●

The pre-tester for HW10 has been released and is ready to use.