list2104.cpp

teach yourself C++ in 21 days 第五版

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

#ifndef DEBUG
   #define ASSERT(x)
#else
   #define ASSERT(x) \
         if (! (x)) \
         { \
            cout << "ERROR!! Assert " << #x << " failed" << endl; \
            cout << " on line " << __LINE__  << endl; \
            cout << " in file " << __FILE__ << endl;  \
         }
#endif


const int FALSE = 0;
const int TRUE = 1;
typedef int BOOL;


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

    char & operator[](int offset);
    char operator[](int offset) const;

    String & operator= (const String &);
    int GetLen()const { return itsLen; }
    const char * GetString() const { return itsString; }
    BOOL Invariants() const;

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

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

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

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

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

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

// operator equals, frees existing memory
// then copies string and size
String& String::operator=(const String & rhs)
{
    ASSERT(Invariants());
    if (this == &rhs)
       return *this;
    delete [] itsString;
    itsLen=rhs.GetLen();
    itsString = new char[itsLen+1];
    for (int i = 0; i < itsLen;i++)
       itsString[i] = rhs[i];
    itsString[itsLen] = '\0';
    ASSERT(Invariants());
    return *this;
}
 
//non constant offset operator
char & String::operator[](int offset)
{
    ASSERT(Invariants());
    if (offset > itsLen)
    {
       ASSERT(Invariants());
       return itsString[itsLen-1];
    }
    else
    {
       ASSERT(Invariants());
       return itsString[offset];
    }
}
 
// constant offset operator
char String::operator[](int offset) const
{
    ASSERT(Invariants());
    char retVal;
    if (offset > itsLen)
       retVal = itsString[itsLen-1];
    else
       retVal = itsString[offset];
    ASSERT(Invariants());
    return retVal;
}
 
BOOL String::Invariants() const
{
    #ifdef SHOW_INVARIANTS
       cout << "String Tested OK ";
    #endif
    return ( (itsLen && itsString) || (!itsLen && !itsString) );
}
 
class Animal
{
   public:
     Animal():itsAge(1),itsName("John Q. Animal")
        {ASSERT(Invariants());}
     Animal(int, const String&);
     ~Animal(){}
     int GetAge() {  ASSERT(Invariants()); return itsAge;}
     void SetAge(int Age)
     {
       ASSERT(Invariants());
       itsAge = Age;
       ASSERT(Invariants());
     }
     String& GetName()
     {
       ASSERT(Invariants());
       return itsName;
     }
     void SetName(const String& name)
     {
       ASSERT(Invariants());
       itsName = name;
       ASSERT(Invariants());
     }
     BOOL Invariants();
   private:
     int itsAge;
     String itsName;
};
 
Animal::Animal(int age, const String& name):
    itsAge(age),
    itsName(name)
{
    ASSERT(Invariants());
}
 
BOOL Animal::Invariants()
{
    #ifdef SHOW_INVARIANTS
       cout << "Animal Tested OK ";
    #endif
       return (itsAge > 0 && itsName.GetLen());
}
 
int main()
{
    Animal sparky(5,"Sparky");
    cout << endl << sparky.GetName().GetString() << " is ";
    cout << sparky.GetAge() << " years old.";
    sparky.SetAge(8);
    cout << endl << sparky.GetName().GetString() << " is ";
    cout << sparky.GetAge() << " years old.";
    return 0;
}