Custom Data Types

Custom Data Types are those defined by the programmer. They included structures, classes, objects, and the like. They allow closely related data to be referenced using a single variable name and element identifiers.

Visual Basic | Delphi | C++ Builder

Visual Basic 6.0

The following is based on the Visual Basic help files. Search for Type statement.

Private Type SystemInfo
  CPU As Variant
  Memory As Long
  VideoColors As Integer
  DiskDrives() As String      ' Dynamic array
  CDDrives(5) As String       ' Fixed-size array
  Cost As Currency
  PurchaseDate As Variant
  temp$                       ' This fails, must use As String
  tempStr As String
End Type

dim myVariable as SystemInfo
Dim AllSystems(100) As SystemInfo

myVarialbe.CPU = "486"         
tempVar = myVarialbe.CPU
myVariable.temp2$ = "whatever" ' The dollar sign is ok here and refers
                               '  to the same variable as omitting it

ReDim myVariable.DiskDrives(5) ' Must set size before using

  ' The help does not say if the size of dynamic arrays 
  ' is set once for all instances or once for each instance
AllSystems(5).DiskDrives(2) = "100M SCSI"

When using Enumerated data types, the command to list the possible options shows only those in the enumerated type definition.

Delphi

type
  TForm1 = class(TForm)
    UIEdit: TEdit;
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

  TMyRecord = record
    a: Integer;
    b: string;
  end;

In a set, each bit represents a separate value. Up to 256 bits (32 bytes) are allowed. Each element of the set is represented by an 8-bit integer. Individual bits can be set and cleared, as well as groups of bits. (To find this in the Delphi 5 help, search for Memory management and step forward until Set types is displayed.)

type
  TMySet = [1, 2, 3];
  TMySetVar = set of TMySet;

  TMySetVar = set of [1, 2, 3];  // Same as Previous 2 lines

  var MySet: set of 'a'..'z';    // from Delphi help on "sets"
   ...
  MySet := ['a','b','c'];        // Set 3 of 26 possible bits
  if 'a' in MySet then ...       // Test if a bit is set
     { do something } ;
  Include (MySet, 'd');   // equivalent to MySet := MySet + ['d'] but more efficient 
  Exclude (MySet, 'd');   // equivalent to MySet := MySet - ['d'] but more efficient

Enumerated - an ordered set of values referenced by identifiers
(Be careful to use a good naming convention here)

type TSuit = (tsClub, tsDiamond, tsHeart, tsSpade);
var
 xx : TSuit;

  xx := tsClub;

When using Ctrl-Space to list the possible options, only those in the enumerated type are displayed.

Warning: If you place the cursor on enum and press F1, the following IDL syntax is provided. This syntax can not be used in a Delphi unit (*.pas file).

typedef enum {Clemens=21, Palmer=22, Ryan=34} pitchers;

C++ Builder

typedef struct
{
  char  a;
  short b;
  long  c;
} tempStruct;

tempStruct temp;          // This allocates space on the stack

temp.a = 'x';
temp.b =  5 ;
temp.c = temp.b

tempStruct* tempPtr = 0;  // =0 is a safety, it is not required, but should be
tempPtr = new tempStruct; // This allocates space on the heap

tempPtr->a = 'x';
tempPtr->b =  5 ;
tempPtr->c = tempPtr->b

tempStruct& tempRef = *new tempStruct; // Must initialize reference when it is created
tempStruct& tempRef;                   // Simply allocating a Reference is Not allowed
tempRef = *temp                        // This is ok

tempRef.a = 'x';
tempRef.b =  5 ;
tempRef.c = temp.b

Author: Robert Clemenzi - clemenzi@cpcug.org