b6_9.cxx

b6_9.cxx

#include ‹stream.hxx›

#include ‹string.h›

extern void exit(int);

class string {

 struct srep {

  char* s;

  int n;

 };

 srep *p;

public:

 string(char *);

 string();

 string(string&);

 string& operator=(char *);

 string& operator=(string&);

 ~string();

 char& operator[](int i);

 friend ostream& operator‹‹(ostream&, string&);

 friend istream& operator››(istream&, string&);

 friend int operator==(string&x, char *s)

  { return strcmp(x.p-›s, s) == 0; }

 friend int operator==(string&x, string&y)

  { return strcmp(x.p-›s, y.p-›s) == 0; }

 friend int operator!=(string&x, char *s)

  {return strcmp(x.p-›s, s) != 0;}

 friend int operator!=(string&x, string&y)

  {return strcmp (x.p-›s, y.p-›s) != 0;}

};

string::string()

{

 p = new srep;

 p-›s = 0;

 p-›n = 1;

}

string::string(char* s)

{

 p = new srep;

 p-›s = new char[strlen(s) +1];

 strcpy(p-›s, s);

 p-›n = 1;

}

string::string(string& x)

{

 x.p-›n++;

 p = x.p;

}

string::~string()

{

 if (--p-›n - 0) {

  delete p-›s;

  delete p;

 }

}

string& string::operator=(char* s)

{

 if (p-›n › 1) {

  p-›n--;

  p = new srep;

 }

 else if (p-›n == 1)

  delete p-›s;

 p-›s = new char[strlen(s)+1];

 strcpy(p-›s, s);

 p-›n = 1;

 return *this;

}

string& string::operator=(string& x)

{

 x.p-›n++;

 if (--p-›n == 0) {

  delete p-›s;

  delete p;

 }

 p = x.p;

 return *this;

}

ostream& operator‹‹(ostream& s, string& x)

{

 return s ‹‹ x.p-›s ‹‹ " [" ‹‹ x.p-›n ‹‹ "] ";

}

istream& operator››(istream& s, string& x)

{

 char buf[256];

 s››buf;

 x = buf;

 cout ‹‹ "echo: " ‹‹ x ‹‹ " ";

 return s;

}

void error(char* p)

{

 cout ‹‹ p ‹‹ " ";

 exit(1);

}

char& string::operator[](int i)

{

 if (i‹0 || strlen(p-›s)‹i) error("index out of range");

 return p-›s[i];

}

main()

{

 string x[100];

 int n;

 cout ‹‹ "here we go ";

 for (n = 0; cin››x[n]; n++) {

  string y;

  if (n==100) error("too many strings");

  cout ‹‹ (y = x[n]);

  if (y=="done") break;

 }

 cout ‹‹ "here we go back again ";

 for (int i=n-1; 0‹=i; i--) cout ‹‹ x[i];

}