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Using the new TStringy class
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| 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.
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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.
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| | 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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