Lab Assignment 5 Solution

**Note**:
For this lab assignment,

you ONLY upload `UTF8string.cpp` and `UTF8string.hpp`.

You MUST NOT modify `utf8.h` and `utf8.c` because they are external libraries.

You MUST use `std::string` as a member variable to store the string, and you are recommended to use its member functions to make your code clearer.

You MUST NOT use `std::u16string` or `std::u32string` because you are required to use the `utf8.c` library to deal with Unicode. Your code MUST pass the given test program and have the expected output.

Please write necessary comments for your code.

  Part 1

This lab will use the UTF8 functions that you are now familiar with and willmake you combine C and C++.

You are asked to create a class called UTF8string; the difference between UTF8string and a regular C++ string is that UTF8string knows "characters" when a string only knows bytes.

The following is provided to simplify your work:
  - Test program (`testUTF8string.cpp`)

You must also use utf8.c and utf8.h. However, you should note that some modifications are required for the C++ compiler to know that the code needs to be compiled in C (C and C++ are incompatible in various ways).

``` cpp
#ifdef __cplusplus
extern "C" {
#endif
extern int utf8_charlen(unsigned char *p);
extern int utf8_bytes_to_charpos(unsigned char *s, int pos);
extern ...
#ifdef __cplusplus
}
#endif
```

> The utf8.c and utf8.h provided in sakai have already been modified.

Because rules for finding the right function (the technical name is "resolving") are different in C and C++, this is required to tell the linker that these are C,not C++, functions and that C rules should apply.

You mustn't derive the class from the string class (which wasn't designed as a base class); however, you should use a string attribute to store the string. You are asked to write the four following methods:
  + `length()`, that returns the length IN CHARACTERS of the UTF8string
  + `bytes()`, that returns the number of bytes used for storing the UTF8string
  + `find(string substr)`, that returns the CHARACTER POSITION where substr starts.
  For instance, in "Mais où sont les neiges d'antan", `find()` should find that "sont" starts at character 8, even if 'ù' is stored on two bytes.
  + `replace(UTF8string to_remove, UTF8string replacement)`, that replaces to_remove with replacement.
You'll have to mix C (char *) strings with the C++ std::string type. It's fairly easy to switch between both; there is a constructor that constructs a string from achar * C string passed as parameter; and the method `c_str()` applied to a C++ std::string returns a pointer to a '\0' terminated sequence of C chars.

  Part 2
We'll extend the UTF8string class by adding overloaded operators. You are asked to redefine:  

 + `<<` i.e. support `std::cout << ustr << std::endl;`
 + `+` that gives regular concatenation (if two objects are called u1 and u2, u1 + u2 changes neither u1 nor u2)
 + `+=` to append another string (u1 += u2 changes u1, not u2)
 + `*` for repeating a string n times (if u is "àéèç", u * 2 or 2 * u should return "àéèçàéèç" without changing u)
 + ! for reversing a string (without modifying original string), which means reversing the characters (not the bytes!), for instance if u is "étudiant" (student in French), !u should be "tnaiduté".