====== HW 04 - String library ======

Your task is to implement your own simplified string library, of course, without the help of ''string.h'' library or similar. Below, you are given the header file with declarations of all the required functions. Each declaration has a description of the desired functionality, arguments, and return values. You can freely implement custom helper functions if needed.

<note important>Updated deadline ''Saturday, 5th November''</note>

<note important>
Only the file ''my_string.c'' should be uploaded into BRUTE.
</note>

===== Description =====
  * You should consider all arrays/strings to be dynamically allocated!
  * All strings are expected to be standard null-terminated character arrays.
  * The functions are expected to behave the same as their standard library equivalents unless custom modifications are stated.
  * Brief function description with links. You can find the detailed description from [[https://en.cppreference.com/w/c/string/byte|cppreference.com]] also in the header file.
    * [[https://en.cppreference.com/w/c/string/byte/strspn|strspn()]], [[https://en.cppreference.com/w/c/string/byte/strtok|strtok()]]
      * strtok() - only the first variant of C99 standard is considered
    * [[https://en.cppreference.com/w/c/string/byte/strcat|strcat()]]
      * The return value is through the first argument which is mutated
    * [[https://en.cppreference.com/w/c/string/byte/strstr|strstr_match()]]
      * The second argument is a simplified regexp pattern with ''[]'' character group and ''[^]'' group prohibition operators.
        * Examples of patterns ''He[^abEr-]p A[lp]ex'' or ''C is great[!?]''

You get the header file ''my_string.h'' <del>{{ :courses:be5b99cpl:hw:my_string.zip |here}}</del> {{ :courses:be5b99cpl:hw:my_string_v2.zip |here *UPDATED*}}.

===== Evaluation =====
<note>
Upload your solution into [[https://cw.felk.cvut.cz/brute/|BRUTE]] as a zip archive containing only your ''my_string.c'' source files.
</note>
The maximum number of points is 10.
  * 3 points - strstr_match function
  * 3 points - strtok function
  * 2 points - strspn function
  * 1 point - strcat function
  * 1 point - coding style (structured, commented functions and arguments (e.g. by Doxygen style), separated into functions …)

==== Late submission ====
  * Submission is allowed one week after the deadline with the following penalties:
    * 50% point reduction
    * It is not possible to use ''for'' or ''while'' loops, but only ''do-while'' is allowed.

----
===== my_string.h =====
<code c>
//----------------------------------------------------------------------------------------
/**
 * \file       my_string.h
 * \author     Jiri Ulrich
 * \date       2022/10/31
 * \brief      Simplified string library.
 *
 *  Simplified string library. Only a selected subset of string manipulation functions.
 *  They differ from the standard in certain parts like return vals and mutability of args.
 *
*/
//----------------------------------------------------------------------------------------

#ifndef MY_STRING_H
#define MY_STRING_H

/// Length of the maximum initial segment
/**
  Returns the length of the maximum initial segment (span) of the null-terminated byte string pointed to by dest,
  that consists of only the characters found in the null-terminated byte string pointed to by src.

  \param[in] dest    pointer to the null-terminated byte string to be analyzed
  \param[in] src     pointer to the null-terminated byte string that contains the characters to search for
  \return The length of the maximum initial segment that contains only characters from the null-terminated byte string pointed to by src.
*/
unsigned long strspn(const char *dest, const char *src);

/// Finds the next token in a byte string
/**
  Finds the next token in a null-terminated byte string pointed to by str. The separator characters are identified by null-terminated byte string
  pointed to by delim. This function is designed to be called multiple times to obtain successive tokens from the same string.
  
    - If str is not a null pointer, the call is treated as the first call to strtok for this particular string.
      The function searches for the first character which is not contained in delim. 
      - If no such character was found, there are no tokens in str at all, and the function returns a null pointer.
        If such character was found, it is the beginning of the token. The function then searches from that point on
        for the first character that is contained in delim. 
        - If no such character was found, str has only one token, and future calls to strtok will return a null pointer
        - If such character was found, it is replaced by the null character '\0' and the pointer to the following character
          is stored in a static location for subsequent invocations. 
      - The function then returns the pointer to the beginning of the token 

    - If str is a null pointer, the call is treated as a subsequent call to strtok: the function continues from where it left
      in previous invocation. The behavior is the same as if the previously stored pointer is passed as str. 

  \param[in] str    pointer to the null-terminated byte string to tokenize
  \param[in] delim         pointer to the null-terminated byte string to copy from
  \return Returns pointer to the beginning of the next token or a null pointer if there are no more tokens.
*/
char *strtok(char *str, const char *delim);

/// String concatenation
/**
  Appends a copy of the null-terminated byte string pointed to by src to the end of the null-terminated byte string pointed to by dest.
  The character src[0] replaces the null terminator at the end of dest. The resulting byte string is null-terminated.
  The dest string will be reallocated if needed to fit the src string.

  \param[in,out] dest    pointer to the null-terminated byte string to append to
  \param[in] src         pointer to the null-terminated byte string identifying delimiters
*/
void strcat(char **dest, const char *src);

/// Substring matching
/**
  Finds the first occurrence of the null-terminated byte string pointed to by substr in the null-terminated byte string pointed to by str.
  The terminating null characters are not compared. The substr may contain the following subset of the regex syntax:
    []        - character groups
    [^]       - group prohibition

  \param[in] str         pointer to the null-terminated byte string to examine
  \param[in] substr      pointer to the null-terminated byte string to search for
  \param[out] begin      pointer to the beginning of the found substring or null pointer if not found
  \return The length of the found substring segment.
*/
unsigned long strstr_match(const char *str, const char *substr, const char **begin);

#endif // MY_STRING_H
</code>
----