Record

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A record is a highly structured data type in Pascal. They are widely used in Pascal, to group data items together logically.

While simple data structures such as arrays or sets consist of elements all of the same type, a record can consist of a number of elements of different types, and can take on a huge complexity. Each separate part of a record is referred to as a field.

The word record is a reserved word.

Declaration

Fixed structure

type
	TMember = record
		firstname, surname : string;
		address: array [1..3] of string;
		phone: string;
		birthdate: TDateTime;
		paidCurrentSubscription: boolean
	end;

Variable structure

And even more complex structures are possible, e.g.:

type
	TMaritalState = (unmarried, married, widowed, divorced);
	TPerson = record
		// CONSTANT PART
		// of course records may be nested
		name: record
			first, middle, last: string;
		end;
		sex: (male, female);
		// date of birth
		dob: TDateTime;
		// VARIABLE PART
		case maritalState: TMaritalState of
			unmarried: ( );
			married, widowed: (marriageDate: TDateTime);
			divorced: (marriageDateDivorced, divorceDate: TDateTime;
				isFirstDivorce: boolean)			
	end;

Note that fields of the variable part have to be in parentheses. You cannot use the same identifier multiple times, so a slightly different name has to be used for the marriageDate in case of divorced.

The variable part shares the same memory. So marriageDate and marriageDateDivorced will have the same value regardless of maritalState. This behaviour is particularly practical as the following example shows:

type
  TSpecialWord = record
    case Byte of
      0: (Word_value: Word);                      // 7
      1: (Byte_low, Byte_high: Byte);             // 7, 0
      2: (Bits: bitpacked array [0..15] of 0..1); // 1, 1, 1, 0, 0, ...
  end;

This record has only a variable part and enables access to the value of the word, the individual bytes and even to the bits. An identifier is not necessarily required in the case clause, so this does not occupy any memory. The size of this record is two bytes. In the case of Bits, this is only possible if bitpacked is used. Note the order of the bytes, with the less significant byte (LSB) coming first.

Advanced record

An “advanced record” is a record with methods, properties and management_operators

  Note: Remember to add a compiler directive {$modeSwitch advancedRecords} (after you have set the mode).

Addressing

Fields

Individual fields are accessed by placing a dot between the record name and the field name thus:

	a.firstname := 'George';
	a.surname := 'Petersen';
	a.phone := '789534';
	a.paidCurrentSubscription := true;

Alternatively, the whole series of fields can be made available together using the with-construct:

with a do
begin
	firstname := 'George';
	surname := 'Petersen';
	phone := '789534';
	paidCurrentSubscription := true
end;

Instances

A record is treated by the program as a single entity, and for example a whole record can be copied (provided the copy is of the same type) thus:

var
	a, b: TMember;

(* main program *)
begin
	// ... assign values to the fields in record a
	b := a
	// Now b holds a _copy_ of a.
	// Do not get confused with references:
	// a and b still point to _different_ _entities_ of TMember.
end.

Constant record

type
	// record definition
	TSpecialDay = record
		dayName: string;
		month: integer;
		day: integer;
	end;

const
	// TSpecialDay constant
	christmasDay: TSpecialDay = (
		dayName: 'Christmas Day';
		month: 12;
		day: 25;
	);

// since FPC 3.2.0 you may define an constant array of records like this
const
   SpecialDays: array of TSpecialDay = (
     ( dayName: 'Christmas Day' ; month: 12; day: 25),
     ( dayName: 'New Year''s Day'; month:  1; day:  1)
   );

Records compared to other structured types

Feature	Record	Adv Record	Object	Class
Encapsulation (combining data and methods + hiding visibility)	No	Yes	Yes	Yes
Inheritance	No	No	Yes	Yes
Class constructor and destructor	No	Yes	Yes	Yes
Polymorphism (virtual methods)	No	No	Yes	Yes
Memory allocation	Stack	Stack	Stack	Heap (Only)
Setting fields to zero on allocation	Managed Types only	Managed Types only	Managed Types only	All fields
Default() function returns a constant with	all fields zeros	all fields zeros	all fields zeros	returns nil
Operator overload (global)	Yes	Yes	Yes	Yes
Operator overload (in type only)	No	Yes	No	No
Type helpers	No	Yes	No	Yes
Virtual constructors, class reference	No	No	No	Yes
Variant part (case) as c/c++ union	Yes	Yes	No	No
Bitpacked (really packing)	Yes	Yes	No	No

Modified from https://forum.lazarus.freepascal.org/index.php/topic,30686.30.html (original author: ASerge).

See also

• Records, tutorial that covers records
• object
• class