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  Using the new TStringy class
The whole Stringy unit
Now that we have created the new Stringy unit bit by bit, here it is in all its glory:
 
 // This unit contains a utility class called TStringy.
 // It is intended to be used for processing a single string in complex ways.
 
 unit Stringy;
 
 interface
 
 type
   // Define the new TStringy class
   TStringy = Class
     // These variables and methods are not visible outside this class
     // They are purely used in the implementation below
     // Note that variables are all prefixed bt 'st'. This allows us, for example
     // to use 'WordCount' as the property name - properties cannot use the same
     // name as a variable.
     private
       stText         : String;    // The string passed to the constructor
       stWordCount    : Integer;   // Internal count of words in the string
       stFindString   : String;    // The substring used by FindFirst, FindNext
       stFindPosition : Integer;   // FindFirst/FindNext current position
 
       procedure GetWordCount;                  // Calculates the word count
       procedure SetText(const Value: String);  // Changes the text string
 
     // These methods and properties are all usable by instances of the class
     published
       // Called when creating an instance (object) from this class
       // The passed string is the one that is operated on by the methods below
       constructor Create(Text : String);
 
       // Utility to replace all occurences of a substring in the string
       // The number of replacements is returned
       // This utility is CASE SENSITIVE
       function Replace(fromStr, toStr : String) : Integer;
 
       // Utility to find the first occurence of a substring in the string
       // The returned value is the found string position (strings start at 1)
       // if not found, -1 is returned
       // This utility is CASE SENSITIVE
       function FindFirst(search : String) : Integer;
 
       // Utility to find the next occurence of the FindFirst substring
       // if not found, -1 is returned
       // if no FindFirst performed before this call, -2 is returned
       // This utility is CASE SENSITIVE
       function FindNext : Integer;
 
       // The string itself - allow it to be read and overwritten
       property Text : String
           read stText
          write SetText;    // We call a method to do this
 
       // The number of words in the document. Words are groups of characters
       // separated by blanks, tabs, carriage returns and line feeds
       property WordCount : Integer
           read stWordCount;
   end;
 
 implementation
 
 uses
   // Units used only internally by this class
   SysUtils, StrUtils;
 
 
 // Constructor : Create an instance of the class. Takes a string as argument.
 // -----------------------------------------------------------------------------
 // The passed string is stored, and the number of words it contains is counted
 // The FindFirst function string and position are reset
 constructor TStringy.Create(Text: String);
 begin
   stText         := Text;         // Save the passed string
   stFindPosition := 1;            // Start a search at the string start
   stFindString   := '';           // No find string provided yet
   GetWordCount;                   // Call a subroutine to get the word count
 end;
 
 
 // SetText : Routine to change the text string
 // -----------------------------------------------------------------------------
 // It is important that we call a routine to change the text because we must
 // recalculate the word length, and reposition the find function at the start
 procedure TStringy.SetText(const Value: String);
 begin
   stText         := Value;        // Save the passed string
   stFindPosition := 1;            // Reposition the find mechanism to the start
   GetWordCount;                   // Recalculate the word count
 end;
 
 
 // FindFirst : Finds the first position of a substring in the string
 // -----------------------------------------------------------------------------
 // The passed substring is saved, and the string scanned for an occurence
 // The found string index is returned. If not found, -1 is returned
 function TStringy.FindFirst(search: String): Integer;
 begin
   // Here we sort of cheat - we save the search string and just call
   // FindNext after setting the initial string start conditions
   stFindString   := search;
   stFindPosition := 1;
 
   Result := FindNext;
 end;
 
 
 // FindNext : Finds the next occurence of the substring in the string
 // -----------------------------------------------------------------------------
 // If FindFirst had not been called, -2 is returned
 // If FindFirst had been called, string scanning is resumed where the left off
 // If found, the index position is returned. Of not found, -1 is returned.
 function TStringy.FindNext: Integer;
 var
   index    : Integer;
   findSize : Integer;
 begin
   /// Only scan if we have a valid scan string
   if Length(stFindString) = 0
   then Result := -2
   else
   begin
     // Set the search string size
     findSize := Length(stFindString);
 
     // Set the result to the 'not found' value
     Result := -1;
 
     // Start the search from where we last left off
     index  := stFindPosition;
 
     // Scan the string :
     // We check for a match with the first character of the fromStr as we step
     // along the string. Only when the first character matches do we compare
     // the whole string. This is more efficient.
     // We abort the loop if the string is found.
     while (index <= Length(stText)) and (Result < 0) do
     begin
       // Check the first character of the search string
       if stText[index] = stFindString[1] then
       begin
         // Now check the whole string - setting up a loop exit condition if
         // the string matches
         if AnsiMidStr(stText, index, findSize) = stFindString
         then Result := index;
       end;
 
       // Move along the string
       Inc(index);
     end;
 
     // Position the next search from where the above leaves off
     // Notice that index gets incremented even with a successful match
     stFindPosition := index
   end;
 
   // This subroutine will now exit with the established Result value
 end;
 
 
 // Replace : Replaces all occurences of a substring in the string
 // -----------------------------------------------------------------------------
 // The string is scanned for occurences of the string, replacing where found
 // The number of replacements is returned, or 0 if none performed.
 function TStringy.Replace(fromStr, toStr: String): Integer;
 var
   fromSize, count, index  : Integer;
   newText : String;
   matched : Boolean;
 begin
   // Get the size of the from string
   fromSize := Length(fromStr);
 
   // Start with 0 replacements
   count := 0;
 
   // We will build the target string in the newText variable
   newText := '';
   index := 1;
 
   // Scan the string :
   // We check for a match with the first character of the fromStr as we step
   // along the string. Only when the first character matches do we compare
   // the whole string. This is more efficient.
   while index <= Length(stText) do
   begin
     // Indicate no match for this character
     matched := false;
 
     // Check the first character of the fromStr
     if stText[index] = fromStr[1] then
     begin
       if AnsiMidStr(stText, index, fromSize) = fromStr then
       begin
         // Increment the replace count
         Inc(count);
 
         // Store the toStr in the target string
         newText := newText + toStr;
 
         // Move the index past the from string we just matched
         Inc(index, fromSize);
 
         // Indicate that we have a match
         matched := true;
       end;
     end;
 
     // if no character match :
     if not matched then
     begin
       // Store the current character in the target string, and
       // then skip to the next source string character
       newText := newText + stText[index];
       Inc(index);
     end;
   end;
 
   // Copy the newly built string back to stText - as long as we made changes
   if count > 0 then stText := newText;
 
   // Return the number of replacements made
   Result := count;
 end;
 
 
 // GetWordCount : Subroutine used to calculate the string word count
 // -----------------------------------------------------------------------------
 // The string is scanned for character groups (separated by blanks, tabs etc)
 // The number found is stored in the csWordCount private global variable
 procedure TStringy.GetWordCount;
 const
   // Define word separator types that we will recognise
   LF    = #10;
   TAB   = #9;
   CR    = #13;
   BLANK = #32;
 var
   WordSeparatorSet : Set of Char;  // We will set on only the above characters
   index  : Integer;     // Used to scan along the string
   inWord : Boolean;     // Indicates whether we are in the middle of a word
 begin
   // Turn on the TAB, CR, LF and BLANK characters in our word separator set
   WordSeparatorSet := [LF, TAB, CR, BLANK];
 
   // Start with 0 words
   stWordCount := 0;
 
   // Scan the string character by character looking for word separators
   inWord := false;
 
   for index := 1 to Length(stText) do
   begin
     // Have we found a separator character?
     if stText[index] In WordSeparatorSet
     then
     begin
       // Separator found - have we moved from a word?
       if inWord then Inc(stWordCount);    // Yes - we have ended another word
 
       // Indicate that we are not in a word anymore
       inWord := false;
     end
     else
       // Separator not found - we are in a word
       inWord := true;
   end;
 
   // Finally, were we still in a word at the end of the string?
   // if so, we must add one to the word count since we did not meet a separator
   if inWord then Inc(stWordCount);
 end;
 
 end.


Using the new Stringy unit
The following code illustrates use of the new class. Notice that we have named this unit Main rather than the Unit1 value default that Delphi provides. This clarifies that it is the main unit of our new application. We have a reference to the new Stringy unit in the uses section. We use the ShowMessage function to display the strings and results of functions.
 
Note also how a TStringy object manages all of its internals without encumbering the user with these details. This is called information hiding. The most used feature of object orientation.
 
The result from running this code is shown beneath it.
 
 unit Main;
 
 interface
 
 uses
   Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
   Dialogs,
   Stringy;   // Use our new Stringy unit
 
 type
   TForm1 = class(TForm)
     procedure FormCreate(Sender: TObject);
   private
     { private declarations }
   public
     { public declarations }
   end;
 
 var
   Form1: TForm1;
 
 implementation
 
 {$R *.dfm}
 
 procedure TForm1.FormCreate(Sender: TObject);
 var
   myText   : TStringy;      // Define a TStringy variable
   count    : Integer;       // Holds return value from TStringy method calls
   position : Integer;       // Gives the position during string searching
 begin
   // Create an instance of the TStringy class, with our desired text string
   // Note that we have added TAB (#11),Carriage return (#13) and Line Feed (#10)
   // characters to the string. These are recognised as word separators
   myText := TStringy.Create('The cat sat'+#13#9+'on the'+#11+'BIG mat');
 
   // Show the number of words in our string:
   ShowMessage('Word count = '+IntToStr(myText.WordCount));
 
   // Set up a new string to work on.
   // This illustrates a 'write' property (WordCount can only be read)
   myText.Text := 'In an enriched time there was a Rich man, with a rich sister';
 
   // How many words in our new string?
   ShowMessage('Word count now = '+IntToStr(myText.WordCount));
 
   // Try to replace the word 'rich' with the word 'desolate'
   count := myText.Replace('rich','desolate');
 
   // How did the string replace get on?
   ShowMessage('rich was replaced '+IntToStr(count)+' times');
   ShowMessage(myText.Text);
 
   // Now try to find the string 'rich' - it is no longer in the string
   position := myText.FindFirst('rich');
   if position > 0
   then ShowMessage('''rich'' first index = '+IntToStr(position))
   else ShowMessage('''rich'' was not found in the string now');
 
   // We'll restore the string and look for all occurences of 'rich'
   // Notice how the myText object remembers where it is in the following
   // sequence of calls. This is a huge benefit of object orientation.
   myText.Text := 'In an enriched time there was a Rich man, with a rich sister';
   position := myText.FindFirst('rich');
 
   while position > 0 do
   begin
     ShowMessage('''rich'' found at index : '+IntToStr(position));
     // Find the next occurence
     // Notice that myText also remembers the search string - we do not have
     // to keep providing it.
     position := myText.FindNext;
   end;
 end;
 
 end.

 Word count = 7
 Word count now = 13
 rich was replaced 2 times
 In an endesolateed time there was a Rich man, with a desolate sister
 'rich' was not found in the string now
 'rich' was found at index : 9
 'rich' was found at index : 50


 
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