C++ is a hybrid language and as such offers global functions and class methods. A function must come before it's usage or you can prototype the function.

This KB Post addresses accessing Paradox tables through the BDE using TDatasource, TTable, and TDBGrid. This tutorial was updated for Delphi 2009 but applies to all versions of Delphi.

This code snippet shows you how to get your NIC MAC address using Borland Delphi.

Delphi supports both static and dynamic arrays.

Borland Delphi editor tips and tricks.

This primer is intended for those just getting started in Delphi and focuses on displaying things.

Create a classic "Hello, World" Windows native code Console App using Delphi. This tutorial is based on Borland Developer Suite 2006 but you can use any version of Delphi you wish. In this tutorial, you will create a classic "Hello, World!" windows console application. A console application is a type of Windows application that has FULL access to the Win32 API, but it's GUI is limited to a DOS-like text window. When Windows starts a console application, it creates a text-mode console window where the program can display text and the user can interact with the program via the keyboard.

Object Pascal is generally not case sensitive.

Delphi uses // for a single line comment and both {} and (**) for multiple line comments. Although you can nest different types of multiple line comments, it is recommended that you don't. A special comment. Delphi compiler directives are in the form of {$DIRECTIVE}. Of interest for comments is using the $IFDEF compiler directive to remark out code.

In Delphi, you define constants similar to how you define variables but use the Const keyword instead of the Var keyword. Declare global constants in a unit's interface section and unit constants (scope limited to unit) in the implementation section. Declare local constants above the begin..end block.

Common source code file extensions include:

• .BDSPROJ - Project, Borland Developer Studio project file holds compiler options, etc. This is the file you open.
• .DCU - Delphi Compiled Unit file.
• .DFM - Delphi Win32 form file (a text resource file).
• .DPR - Delphi project file. Primary project "source" file.
• .PAS - Delphi unit source file.

Object Pascal allows parameters of the same type to be listed together, separated by commas, and followed with a single data type (more params of different data types can follow, after a semi-colon). The default for parameters is by value. For by reference, add var in front of the parameter. Object Pascal also offers constant parameters where you add const in front of the parameter. A constant parameter is like a local constant or read-only parameter the compiler can optimize. You cannot assign a value to a constant parameter, nor can you pass one as a var parameter to another routine.

Declare global variables in the interface section of a unit, variables declared within the implementation section (but not within a method) have a scope limited to the unit. You declare local variables in a var block outside (above) your begin..end code block. You cannot declare variables in-line (inside begin..end). You can initialize global and unit variables but you cannot initialize local variables. Delphi offers many variable types. Some common variable types include String, WideString, PChar, Integer, Boolean, Single, Double, Pointer, and Variant.

When you want the exception to be the rule. A technique for handling exceptions in Borland Delphi's Object Pascal.

Common comparison operators:

Object Pascal

• Operator - Yes. But not Pascal.
• Method - Yes.  

Beginners example of creating and using a class. Early versions of Delphi use the standard OO private, protected, and public visibility specifiers plus add published for RTTI info. Later versions of Delphi add strict private and strict protected for a true OO implementation.

Delphi for Win32 supports abstract class members using the abstract keyword. You can even instantiate instances of a class that contains abstract members. Then you override each abstract member in a descendant class with Override. Delphi does not support setting an entire class as abstract. You can create an abstract class (a class with one or more abstract methods), but there is no way to tell the compiler to not allow the instantiation of the abstract class. Delphi does not support abstract member properties directly. To implement an abstract properity, make use of abstract methods. That is, you can read a GetPropertyX abstract function and write to a SetPropertyX abstract procedure. In effect, creating  an abstract property.

In Delphi programming language (Object Pascal), all classes ultimately inherit from the base class TObject.

Delphi allows you to extend an existing class without using inheritance. Buggy in 2005 and not officially supported but stable and usable in 2006 and above. You declare a class helper similiar to how you declare a class but use the keywords class helper for.

• You can name a helper anything.
• Helpers have access only to public members of the class.
• You cannot create an object instance directly from a class helper.
• self refers to the class being helped.

Declare your class in the Interface section. Then implement the class in the Implementation section.

In Delphi, use the constructor keyword to signify which method or methods are constructors for a class. It is traditional but not required to use a procedure called Create.

In addition to having multiple named constructors, you can overload constructors.

In Delphi, you use the class keyword followed by the parent class in parens. If you leave out the parent class, your class inherits from TObject.

You specify an interface in the type block just like you do for a class but you use the interface keywoard instead of the class keyword and in the interfaces section only. Since interfaces, by definition, do not have any implementation details, all you do is specifiy it in the type block.

Specify Delphi member modifiers as follows:

reintroduce; overload; [binding modifier]; [calling convention]; abstract; [warning]

The binding modifiers are virtual, dynamic, or override. The calling conventions are register, pascal, cdecl, stdcall, or safecall. The warnings are platform, deprecated, or library. Additional directives include reintroduce, abstract, class, static, overload, and message.

Up until D2005, private and protected were not implemented strictly. Starting with D2005, a traditional strict versions of OOP are supported using the strict keyword. OO purist will want you to use strict private over private and strict protected over protected. I suggest you follow that advice until you both fully understand the differences and have a specific need. Delphi offers a special published specifier which is the same as public members but runtime type information (RTTI) is generated.

In Delphi, you specify a virtual method with the virtual keyword in a parent class and replace it in a descendant class using the override keyword. Call Inherited in the descendant method to execute the code in the parent method.

Our Delphi Gazette ran for a vew years in the late 90s. This page archives 1998.

C# is case sensitive. The following does NOT:

messagebox.Show("hello");  //Does not work!

The first time you type any other case for commands or variables, VS.Net will change it to the accepted or defined case. For example, if you type messagebox.show it is converted to MessageBox.Show. Once corrected, you can break it again by editing MessageBox to messagebox and the compiler will give you an error.

C# supports abstract class members and abstract classes using the abstract modifier. An abstract class is a class with one or more abstract members and you cannot instantiate an abstract class. However, you can have additional implemented methods and properties. An abstract member is either a method (implicitly virtual), property, indexer, or event in an abstract class. You can add abstract members ONLY to abstract classes using the abstract keyword.

In C#, you use the class keyword to specify a class and you signify its parent with a colon and the name of the parent class. When you instantiate an object from a class, you use the new keyword.

In C#, a constructor is called whenever a class or struct is created. A constructor is a method with the same name as the class with no return value and you can overload the constructor. If you do not create a constructor, C# will create an implicit constructor that initializes all member fields to their default values.

Constructors can execute at two different times. Static constructors are executed by the CLR before any objects are instantiated. Regular constructors are executed when you create an object.

Use a destructor to free unmanaged resources. A destructor is a method with the same name as the class but preceded with a tilde (as in ~ClassName). The destructor implicity creates an Object.Finalize method (you cannot directly call nor override the Object.Finalize method).

In C# you cannot explicitly destroy an object. Instead, the .Net Frameworks garbage collector (GC) takes care of destroying all objects. The GC destroys the objects only when necessary. Some situations of necessity are when memory is exhausted or you explicitly call the System.GC.Collect method. In general, you never need to call  System.GC.Collect.

Classes and structs can inherit from interfaces in a manner similar to how classes can inherit a base class or struct, but a class or struct can inherit more than one interface and it inherits only the method names and signatures, because the interface itself contains no implementations.

class MyClass: IMyInterface

{  

  public object Clone()
  {
  return null; 
  }  

// IMyInterface implemented here...
} 

In C# you can set the visibility of a member field to any visibility: private, protected, public, internal or protected internal. You can intialize a member field with a default when declared. If you set the member field value in your constructor, it will override the default value. Finally, you can use the static modifier (no instance required) and readonly modifier (similar to a constant).

In C#, parens indicate a method and the lack of parens indicate a property. You use special get and set methods to both get and set the values of properties. For a read-only property, leave out the set method. The value keyword is used to refer to the member field. Properties can make use of any of the access modifiers (private, protected, etc). It is common to use a lowercase member names for member fields ("name" in our example) and uppercase properties to manage member fields ("Name" in our example).

Method overriding allows you to define or implement a virtual method in a parent class and then replace it in a descendant class. In C#, you specify a virtual method with the virtual keyword in a parent class and replace it in a descendant class using the override keyword.

C# uses the keyword partial to specify a partial class. All parts must be in the same namespace.

A partial class, or partial type, is a class that can be split into two or more source code files and/or two or more locations within the same source file. Each partial class is known as a class part or just a part. Logically, partial classes do not make any difference to the compiler. The compiler puts the class together at compile time and treats the final class or type as a single entity exactly the same as if all the source code was in a single location.

You can use them for many things including to separate code generator code, organize large classes, divice a class up so you can split ownwership among multiple developers, have different versions of the same class, and to utilize multiple languages with a single class.

The ButtonsCS project. Create a classic "Hello, World" application using Visual Studio .Net with C# syntax. Requires either the full version or Visual C# Express Edition.

This will show how to make a "hello world" console application in Visual Studio 2008 using VB.Net.

VB.Net supports abstract class members and abstract classes using the MustInherit and MustOverride modifiers.An abstract class is indicated with a MustInherit modifier and is a class with one or more abstract members and you cannot instantiate an abstract class. However, you can have additional implemented methods and properties. An abstract member is either a method (implicitly virtual), property, indexer, or event in an abstract class. You can add abstract members ONLY to abstract classes using the MustOverride keyword. Then you override it in a descendant class with Overrides.

Declare and implement VB.Net classes after the form class or in their own .vb files. Unlike VB Classic, you can have more than one class in a .vb class file (VB classic uses .cls files for each class).

 A sub named New. You can overload the constructor simply by adding two or more New subs with various parameters.

Public Class Cyborg
  Public CyborgName As String

  Public Sub New(ByVal pName As String)
    CyborgName = pName
  End Sub
End Class

Use a destructor to free unmanaged resources. A destructor is a method with the same name as the class but preceded with a tilde (as in ~ClassName). The destructor implicity creates an Object.Finalize method (you cannot directly call nor override the Object.Finalize method).

In VB.Net you cannot explicitly destroy an object. Instead, the .Net Frameworks garbage collector (GC) takes care of destroying all objects. The GC destroys the objects only when necessary. Some situations of necessity are when memory is exhausted or you explicitly call the System.GC.Collect method. In general, you never need to call  System.GC.Collect.

With VB.Net you define an interface with the Interface keyword and use it in a class with the Implements keyword. In the resulting class, you implement each property and method and add Implements Interface.Object to each as in:

Sub Speak(ByVal pSentence As String) Implements IHuman.Speak

  MessageBox.Show(pSentence)

End Sub

In VB.Net you can set the visibility of a member field to any visibility: private, protected, public, friend or protected friend.

You can intialize a member field with a default when declared. If you set the member field value in your constructor, it will override the default value.

Finally, you can use the Shared modifier (no instance required) and ReadOnly modifier (similar to a constant).

VB.Net uses a special property keyword along with special get and set methods to both get and set the values of properties. For a read-only property, leave out the set method. The value keyword is used to refer to the member field. Properties can make use of any of the access modifiers (private, protected, etc).

My preference for VB.Net code is to start member fields with "F" ("FName" in our example) and drop the "F" with properties that manage member fields ("Name" in our example).

In VB.Net, you specify a virtual method with the Overridable keyword in a parent class and extend (or replace) it in a descendant class using the Overrides keyword.

Use the base keyword in the descendant method to execute the code in the parent method, i.e. base.SomeMethod().

VB.Net supports both partial classes and partial methods.

If you have an existing Paradox system you can keep using it but you'll need to skip the Vista operating system and either stick with Windows XP or move to Windows 7. Because better tools exist, you may very well want to put a plan together now for converting to another development tool or at least understand what the future is likely to hold. If you're a power-user or researcher working with data, stick with Paradox.

Bottom line is you should skip Vista and either stick with XP or move to Win 7. If you have to use Vista, you might be better off with Paradox 9.

Does Corel Paradox for Windows run on Vista? If so, are there any issues? What about Windows 7?

Procedure for fixing the Could Not Initialize BDE" error.

Paradox 9, 10, 11, etc. install easily on Windows 7! You do have to download WinHelp to get the Paradox help files to work properly.

Instructions to install Paradox 9 for Windows on Vista.

Paradox for Windows has two primary file types: source files and delivered files. Source files in Paradox are binary but can can be opened in later versions of Paradox and even in earlier versions if you don't use any new features: .FSL = Form, .RSL = Report, .SSL = Script, and .LSL = Library. Since Paradox source files do not compile to an EXE, Paradox developers tend to use a startup form or script to start the application.

Paradox does not remember desktop settings. I just installed Paradox 11 on a new computer and my working directory and other settings do not stick when I restart Paradox. Why?

Paradox 9 versions for SP1 through SP4. Plus version info on Paradox 10 and 11.

A trip down memory lane: the icons that shipped with various versions of Paradox.

Use a file server (not a workstation) to store your data, disable Oplocks on the filer server, and configure the BDE (local share to true and optimize if desired). Finally, if workstations are crashing, fix em so they don't. You want clean running computers that don't crash.

Covers ALL Paradox tables from version 4 on including a description of the various Paradox table structures, limits, and specifications.

Step by step instructions for repairing your Paradox tables.

If you've never programmed in ObjectPAL, spend 10 minutes and see how easy it is to program Paradox for Windows.

This detailed ObjectPAL primer will get you up and running developing in Paradox/ObjectPAL within a few hours.

Part 3.

Think levels when you code in the Pardox ObjectPAL development environment.

Common comparison operators:

In ObjectPAL, an empty variable can be unassigned (essentially null) or blank (equivalent to ""). You have to use both isBlank and isAssigned to check for an empty string.

ObjectPAL logical operators:

Step by step instructions for setting some of Paradox's more useful preferences.

Using loop structures in ObjectPAL (for, forEach, scan, while, and looping with timers).

Exploring ObjectPAL's TCursor object type.

Paradox has a built-in report writer that will suffice for nearly all reports you wish to create. You base a report on one or more tables or on a query. It uses a banded approach so you think in terms of records, pages, and report. Except for the record band, each section has a header and a footer. Paradox also offers a quick report which is useful for printing data quickly.

You can use Format | Filter while viewing a table to apply a secondary index.

Using Paradox internet features. Content from chapter 25 of my "Paradox Power Programming: The Official Guide" book.

Using extended uses in ObjectPAL example.

Paradox for Windows Command-Line Options, runtime registry settings, adding menu items to Paradox, and manually setup a Vista shortcut.

Listing of Paradox features NOT available in Paradox Runtime.

Forward to my book Paradox 9 Power Programming: The Official Guide. The forward is by Michael Cowpland (Chairman, President and CEO, Corel Corporation).

Chapter 4, "An Introduction to ObjectPAL" from Paradox 9 Power Programming by Mike Prestwood.

Chapter 12, "Handling Reports" from Paradox 9 Power Programming by Mike Prestwood.

Chapter 16, "Handling the Keyboard" from Paradox 9 Power Programming by Mike Prestwood.

Chapter 24 "SQL and Client/Server Applications" of Paradox 9 Power Programming by Mike Prestwood.

This chapter will introduce you to creating both menus and pop-up menus. If you are going to create an application-wide menu, then I strongly recommend you use Paradox’s Application Framework. This chapter will instruct you how to create menus for non-Application Framework applications and pop-up menus you can use with both.

For maximum compatibility, use compatibility mode and adjust settings (640x480, and run in a Window, etc.).

Chapter 26 by Mike Prestwood from the book WordPerfect Office 2000 for Linux: The Official Guide. First published June 2000 by Osborne-McGraw/Hill. ISBN 0-07-212238-2.

Chapter 27 by Mike Prestwood from the book WordPerfect Office 2000 for Linux: The Official Guide. First published June 2000 by Osborne-McGraw/Hill. ISBN 0-07-212238-2.

Chapter 28 by Mike Prestwood from the book WordPerfect Office 2000 for Linux: The Official Guide. First published June 2000 by Osborne-McGraw/Hill. ISBN 0-07-212238-2.

Chapter 29 by Mike Prestwood from the book WordPerfect Office 2000 for Linux: The Official Guide. First published June 2000 by Osborne-McGraw/Hill. ISBN 0-07-212238-2.

Commenting Code
VB Classic, like all the VB-based languages, uses a single quote (') or the original class-style basic "REM" (most developers just use a quote). VB Classic does NOT have a multiple line comment.

Directives - #

Directives are sometimes called compiler or preprocessor directives. A # is used for directives within VB Classic code. VB Classic offers only an #If..then/#ElseIf/#Else directive.

VB Classic is a loosely typed language. Declaring variables is optional unless you use the Option Explicit statement to force explicit declaration of all variables with Dim, Private, Public, or ReDim. Using Option Explicit is strongly recommended to avoid incorrectly typing an existing variable and to avoid any confusion about variable scope.

Undeclared variables are variants. To specifically declare a variant, use:

Dim x As Variant

Dim x 

Common data types include Byte (0..255), Boolean, Integer (2-byte integers), Long (4-byte integers), Currency, Single (32-bit number), Double (64-bit number), Date, String, and variant.

Variables declared with Dim at the module level are available to all procedures within the module. At the procedure level, variables are available only within the procedure.

VB Classic logical operators:

VB Classic is a non-OOP language with some OOP features. It offers both Subs and Functions. A Sub does not return a value while a Function does. When Subs and Functions are used in a class module, they become the methods of the class.

Arrays in ASP Classic use a 0-based indice.

Use UBound to get the number of elements. UBound returns -1 if the array has no elements, 0 if it has 1, 1 if it has 2, etc.

In ASP Classic, you have to add an empty string to the value being compared in order to get consistent results. For example, add &"" to your string varilable or it's code equivalent &vbNullString. Then compare to an empty string or verify it's length to 0 with Len.

An example of using ASP's Response.Write and creating functions.

The End If is optional if you put your code on a single line.

Same as VB. ASP Classic logical operators:

Use Application.Contents.RemoveAll and Session.Contents.RemoveAll

How to use ASPMail to send email from your web site.

Use the scriptiing dictionary object which is available on later versions of ASP Classic (all still commonly in use). Both Access VBA and VB Classic use a collection for this but collections are not supported in ASP Classic.

Dim StateList

Set StateList = Server.CreateObject("Scripting.Dictionary")
StateList.Add "CA", "California"

StateList.Add "NV", "Nevada" 

Response.Write "I live in " & StateList.Item("CA")

Response.Flush sends the contents of the buffer to the browser. This command is useful for showing a visitor something while slow loading pages load.

Ultra-primitive (no inheritance) but useful and encourages you to think and design using objects.

When an object instance is created from a class, ASP calls a special parameter-less sub named Class_Initialize. Since you cannot specify parameters for this sub, you also cannot overload it.

When a class is destroyed, ASP calls a special sub called Class_Terminate.

When an object instance is destroyed, ASP calls a special parameter-less sub named Class_Terminate. For example, when the variable falls out of scope. Since you cannot specify parameters for this sub, you also cannot overload it.

When an object instance is created from a class, ASP calls a special sub called Class_Initialize.

ASP classic uses the property keyword and special Get and Let methods to both get and set the values of properties.

The member visibility modifiers are Private and Public. If not specified, the default is Public. Private and Public have the usual meaning. Private members are visible only within the class block. Public members are visible within the class and outside of the class.