list1314.cpp

teach yourself C++ in 21 days 第五版

//Listing 13.14 Using a String class

#include <iostream>
#include <string.h>
using namespace std;

// Rudimentary string class
class String
{
  public:
    // constructors
    String();
    String(const char *const);
    String(const String &);
    ~String();

    // overloaded operators
    char & operator[](unsigned short offset);
    char operator[](unsigned short offset) const;
    String operator+(const String&);
    void operator+=(const String&);
    String & operator= (const String &);

    // General accessors
    unsigned short GetLen()const { return itsLen; }
    const char * GetString() const { return itsString; }

  private:
    String (unsigned short);         // private constructor
    char * itsString;
    unsigned short itsLen;
};

// default constructor creates string of 0 bytes
String::String()
{
   itsString = new char[1];
   itsString[0] = '\0';
   itsLen=0;
}

// private (helper) constructor, used only by
// class methods for creating a new string of
// required size. Null filled.
String::String(unsigned short len)
{
   itsString = new char[len+1];
   for (unsigned short i = 0; i<=len; i++)
      itsString[i] = '\0';
   itsLen=len;
}

// Converts a character array to a String
String::String(const char * const cString)
{
   itsLen = strlen(cString);
   itsString = new char[itsLen+1];
   for (unsigned short i = 0; i<itsLen; i++)
      itsString[i] = cString[i];
   itsString[itsLen]='\0';
}

// copy constructor
String::String (const String & rhs)
{
   itsLen=rhs.GetLen();
   itsString = new char[itsLen+1];
   for (unsigned short i = 0; i<itsLen;i++)
      itsString[i] = rhs[i];
   itsString[itsLen] = '\0';
}

// destructor, frees allocated memory
String::~String ()
{
   delete [] itsString;
   itsLen = 0;
}

// operator equals, frees existing memory
// then copies string and size
String& String::operator=(const String & rhs)
{
   if (this == &rhs)
      return *this;
   delete [] itsString;
   itsLen=rhs.GetLen();
   itsString = new char[itsLen+1];
   for (unsigned short i = 0; i<itsLen;i++)
      itsString[i] = rhs[i];
   itsString[itsLen] = '\0';
   return *this;
}

//nonconstant offset operator, returns
// reference to character so it can be
// changed!
char & String::operator[](unsigned short offset)
{
   if (offset > itsLen)
      return itsString[itsLen-1];
  else
      return itsString[offset];
}

// constant offset operator for use
// on const objects (see copy constructor!)
char String::operator[](unsigned short offset) const
{
  if (offset > itsLen)
      return itsString[itsLen-1];
  else
      return itsString[offset];
}

// creates a new string by adding current
// string to rhs
String String::operator+(const String& rhs)
{
  unsigned short  totalLen = itsLen + rhs.GetLen();
  String temp(totalLen);
  unsigned short i;
  for ( i= 0; i<itsLen; i++)
      temp[i] = itsString[i];
  for (unsigned short j = 0; j<rhs.GetLen(); j++, i++)
      temp[i] = rhs[j];
  temp[totalLen]='\0';
  return temp;
}

// changes current string, returns nothing
void String::operator+=(const String& rhs)
{
  unsigned short rhsLen = rhs.GetLen();
  unsigned short totalLen = itsLen + rhsLen;
  String  temp(totalLen);
  unsigned short i;
  for (i = 0; i<itsLen; i++)
      temp[i] = itsString[i];
  for (unsigned short j = 0; j<rhs.GetLen(); j++, i++)
      temp[i] = rhs[i-itsLen];
  temp[totalLen]='\0';
  *this = temp;
}

int main()
{
  String s1("initial test");
  cout << "S1:\t" << s1.GetString() << endl;

  char * temp = "Hello World";
  s1 = temp;
  cout << "S1:\t" << s1.GetString() << endl;

  char tempTwo[20];
  strcpy(tempTwo,"; nice to be here!");
  s1 += tempTwo;
  cout << "tempTwo:\t" << tempTwo << endl;
  cout << "S1:\t" << s1.GetString() << endl;

  cout << "S1[4]:\t" << s1[4] << endl;
  s1[4]='x';
  cout << "S1:\t" << s1.GetString() << endl;

  cout << "S1[999]:\t" << s1[999] << endl;

  String s2(" Another string");
  String s3;
  s3 = s1+s2;
  cout << "S3:\t" << s3.GetString() << endl;

  String s4;
  s4 = "Why does this work?";
  cout << "S4:\t" << s4.GetString() << endl;
  return 0;
}