Creating Arrays

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4D v20.6

Creating Arrays

You create an array with one of the array declaration commands described in this chapter. The following table lists the array declaration commands:

Command	Creates or resizes an array of
ARRAY INTEGER	2-byte Integer values
ARRAY LONGINT	4-byte Integer values
ARRAY REAL	Real values
ARRAY TEXT	Text values (up to 2 GB of text per element) (*)
_o_ARRAY STRING	Text values (obsolete) (*)
ARRAY DATE	Date values
ARRAY BOOLEAN	Boolean values
ARRAY PICTURE	Pictures values
ARRAY POINTER	Pointer values
ARRAY OBJECT	Language objects
ARRAY BLOB	BLOBs
ARRAY TIME	Times

Each array declaration command can create or resize one-dimensional or two-dimensional arrays. For more information about two-dimensional arrays, see the Two-dimensional Arrays section.

(*) There is no difference between Text and String arrays. The strLen parameter of the _o_ARRAY STRING command is ignored. It is recommended to use Text arrays. The _o_ARRAY STRING command is only kept for compatibility reasons.

The following line of code creates (declares) an Integer array of 10 elements:

ARRAY INTEGER(aiAnArray;10)

Then, the following code resizes that same array to 20 elements:

ARRAY INTEGER(aiAnArray;20)

Then, the following code resizes that same array to no elements:

ARRAY INTEGER(aiAnArray;0)

You reference the elements in an array by using curly braces ({…}). A number is used within the braces to address a particular element; this number is called the element number. The following lines put five names into the array called atNames and then display them in alert windows:

 ARRAY TEXT(atNames;5)

 atNames{1}:="Richard"

 atNames{2}:="Sarah"

 atNames{3}:="Sam"

 atNames{4}:="Jane"

 atNames{5}:="John"

 For($vlElem;1;5)

    ALERT("The element #"+String($vlElem)+" is equal to: "+atNames{$vlElem})

 End for

Note the syntax atNames{$vlElem}. Rather than specifying a numeric literal such as atNames{3}, you can use a numeric variable to indicate which element of an array you are addressing.

Using the iteration provided by a loop structure (ARRAY TO LIST, LIST TO ARRAY or PLAY), compact pieces of code can address all or part of the elements in an array.

Arrays and other areas of the 4D language

There are other 4D commands that can create and work with arrays. More particularly:

To work with arrays and selection of records, use the commands SELECTION RANGE TO ARRAY, SELECTION TO ARRAY, ARRAY TO SELECTION and DISTINCT VALUES.
Objects of the List box type are based on arrays; several commands of the “List box” theme work with arrays, for instance LISTBOX INSERT ROWS.
You can create graphs and charts on series of values stored in tables and arrays. For more information, see the GRAPH command.
The LIST TO ARRAY and ARRAY TO LIST commands.
Many commands can build arrays in one call, for example: FONT LIST, WINDOW LIST, VOLUME LIST, FOLDER LIST, DOCUMENT LIST, GET SERIAL PORT MAPPING, SAX GET XML ELEMENT, etc.