/* Code for exercises 11.8 and 11.10. |  | "C++ Solutions--Companion to The C++ Programming Language, Third Edition" | by David Vandevoorde; Addison-Wesley 1998; ISBN 0-201-30965-3. | | Permission to use, copy, modify, distribute and sell this software | and its documentation for any purpose is hereby granted without fee. | The author makes no representations about the suitability of this | software for any purpose.  It is provided "as is" without express or | implied warranty. `----------------------------------------------------------------------*//*This header contains the String implementation as presented inBjarne Stroustrup's "The C++ Programming Language (third edition)".It is used by ex11_8.cpp and ex11_10.cpp.*/#include <assert.h>#include <iostream>#include <string.h>class String {   struct Srep; // Internal representation.   Srep *rep;   friend struct String_iter;public:   class Cref; // Behaves somewhat like char&.   class Range {}; // For exceptions.    // Creation, copying and destruction:   inline String(); // x = ""   inline String(char const*); // x = "abc"   inline String(String const&); // x = other_string   inline String& operator=(char const*);   inline String& operator=(String const&);   inline ~String();   // Access and bounds-checking:   inline void check(int) const;   inline char read(int) const;   inline void write(int, char);   inline char operator[](int) const;   inline Cref operator[](int);   inline int size() const;   // Access to C-style representation (Exercise 11.10):   char const* c_string() const;   // Substring operator (Exercise 11.8):   inline String operator()(int left, int right);   // Relational operators:   friend bool operator==(String const&, char const*);   friend bool operator==(String const&, String const&);   friend bool operator!=(String const&, char const*);   friend bool operator!=(String const&, String const&);   // Concatenation:   inline String* operator+=(char const*); // Exercise.   inline String& operator+=(String const&); // Exercise.   // Formatted I/O:   friend ostream& operator<<(ostream&, String const&); // Exercise.   friend istream& operator>>(istream&, String&); // Exercise.};// Internal representation of a String (with sharing):struct String::Srep {   char *s; // Pointer to array of chars (elements).   int sz; // Number of chars.   int n; // Reference count.   Srep(int nsz, char const *p) {      n = 1;      sz = nsz;      s = new char[sz+1]; // Add space for terminator.      strcpy(s, p);   }   ~Srep() { delete[] s; }   Srep* get_own_copy() { // Clone if necessary.      if (n==1) { return this; }      --n;      return new Srep(sz, s);   }   void assign(int nsz, char const *p) {      if (sz!=nsz) {         delete[] s;         sz = nsz;         s = new char[sz+1];      }      strcpy(s, p);   }private: // Prevent copying   Srep(Srep const&);   Srep& operator=(Srep const&);};// Dispatcher (proxy, helper) for writing to a char in a String:class String::Cref { // Reference to s[i]   friend class String;   String &s;   int i;   Cref(String &ss, int ii): s(ss), i(ii) {}public:   operator char() { return s.read(i); } // Yield value.   void operator=(char c) { s.write(i, c); } // Change value.};// String members functions:inline String::String() { rep = new Srep(0, ""); }inline String::String(char const *s) { rep = new Srep(strlen(s), s); }inline String::String(String const &x) { // Copy constructor.   ++(x.rep->n);   rep = x.rep; // Share representation.}inline String& String::operator=(char const *s) {   if (rep->n==1) { rep->assign(strlen(s), s); } // Recycle Srep.   else { // Use new Srep.      --(rep->n);      rep = new Srep(strlen(s), s);   }   return *this;}inline String& String::operator=(String const &x) { // Copy assignment.   ++(x.rep->n); // Protect against "str = str;"   if (--(rep->n)==0) { delete rep; }   rep = x.rep; // Share representation.   return *this;}inline String::~String() { if (--(rep->n)==0) { delete rep; } }inline void String::check(int i) const {   if (i<0 || rep->sz<=i) {      throw Range();   }}inline char String::read(int i) const { return rep->s[i]; }char String::operator[](int i) const { check(i); return rep->s[i]; }inline void String::write(int i, char c) {   rep = rep->get_own_copy();   rep->s[i] = c;}inline String::Cref String::operator[](int i) {   check(i);   return String::Cref(*this, i);}inline int String::size() const { return rep->sz; }inline bool operator==(String const &x, char const *s) {   return strcmp(x.rep->s, s)==0;}inline bool operator==(String const &x, String const &y) {   return strcmp(x.rep->s, y.rep->s)==0;}inline bool operator!=(String const &x, char const *s) {   return strcmp(x.rep->s, s)!=0;}inline bool operator!=(String const &x, String const &y) {   return strcmp(x.rep->s, y.rep->s)!=0;}