Ok, long code...and really short and quick Question and most probably answer.

This is a discussion on Ok, long code...and really short and quick Question and most probably answer. within the C++ Programming forums, part of the General Programming Boards category; Ok, I think that I pretty much got it now, but I have one question, it's in bold. Before that, ...

  1. #1
    left crog... back when? incognito's Avatar
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    Ok, long code...and really short and quick Question and most probably answer.

    Ok, I think that I pretty much got it now, but I have one question, it's in bold. Before that, why is it necessary to include the <string.h> header?


    //Listing 13.12 Using a String class
    Code:
    #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. Why must it all be filled with null 
    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;
     int x;
     cin>>x;
    	return 0;
    }
    Last edited by incognito; 01-22-2002 at 11:37 PM.
    There are some real morons in this world please do not become one of them, do not become a victim of moronitis. PROGRAMMING IS THE FUTURE...THE FUTURE IS NOW!!!!!!!!!

    "...The only real game I thank in the world is baseball..." --Babe Ruth

    "Life is beautiful"-Don Corleone right before he died.

    "The expert on anything was once a beginner" -Baseball poster I own.


    Left cprog on 1-3-2005. Don't know when I am coming back. Thanks to those who helped me over the years.

  2. #2
    &TH of undefined behavior Fordy's Avatar
    Join Date
    Aug 2001
    Posts
    5,789
    Just a safety thing...stops the array being filled with garbage from the beginning.

    Also if you try use it in cout or something you will have an empty string, as the first element of the array is the NULL char.

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