6.05-友元类.cpp

Visual C++的课件

//Listing 15.8 - friendly operators

#include <iostream.h>
#include <string.h>

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

	// overloaded operators
	char & operator[](int offset);
	char operator[](int offset) const;
	String operator+(const String&);
	friend String operator+(const String&, const String&);
	void operator+=(const String&);
	String & operator= (const String &);

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

private:
	String (int);         // 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;
	// cout << "\tDefault string constructor\n";
	// ConstructorCount++;
}

// 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;
	// cout << "\tString(int) constructor\n";
	// ConstructorCount++;
}

// 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';
	// cout << "\tString(char*) constructor\n";
	// ConstructorCount++;
}

// 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';
	// cout << "\tString(String&) constructor\n";
	// ConstructorCount++;
}

// destructor, frees allocated memory
String::~String ()
{
	delete [] itsString;
	itsLen = 0;
	// cout << "\tString destructor\n";
}

// 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 (int i = 0; i<itsLen;i++)
		itsString[i] = rhs[i];
	itsString[itsLen] = '\0';
	return *this;
	// cout << "\tString operator=\n";
}

//non constant offset operator, returns
// reference to character so it can be
// changed!
char & String::operator[](int 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[](int 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)
{
	int  totalLen = itsLen + rhs.GetLen();
	String temp(totalLen);
	int i, j;
	for (i = 0; i<itsLen; i++)
		temp[i] = itsString[i];
	for (j = 0, i = itsLen; j<rhs.GetLen(); j++, i++)
		temp[i] = rhs[j];
	temp[totalLen]='\0';
	return temp;
}

// creates a new string by adding
// one string to another
String operator+(const String& lhs, const String& rhs)
{
	int  totalLen = lhs.GetLen() + rhs.GetLen();
	String temp(totalLen);
	int i, j;
	for (i = 0; i<lhs.GetLen(); i++)
		temp[i] = lhs[i];
	for (j = 0, i = lhs.GetLen(); j<rhs.GetLen(); j++, i++)
		temp[i] = rhs[j];
	temp[totalLen]='\0';
	return temp;
}

int main()
{
	String s1("String One ");
	String s2("String Two ");
	char *c1 = { "C-String One " } ;
	String s3;
	String s4;
	String s5;

	cout << "s1: " << s1.GetString() << endl;
	cout << "s2: " << s2.GetString() << endl;
	cout << "c1: " << c1 << endl;
	s3 = s1 + s2;
	cout << "s3: " << s3.GetString() << endl;
	s4 = s1 + c1;
	cout << "s4: " << s4.GetString() << endl;
	s5 = c1 + s2;
	cout << "s5: " << s5.GetString() << endl;
	return 0;
}