Two-dimensional Arrays

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4D v15.4

4D Language Reference

Arrays

Two-dimensional Arrays

Each of the array declaration commands can create or resize one-dimensional or two-dimensional arrays. Example:

ARRAY TEXT(atTopics;100;50) ` Creates a text array composed of 100 rows of 50 columns

Two-dimensional arrays are essentially language objects; you can neither display nor print them.

In the previous example:

atTopics is a two-dimensional array
atTopics{8}{5} is the 5th element (5th column...) of the 8th row
atTopics{20} is the 20th row and is itself a one-dimensional array
Size of array(atTopics) returns 100, which is the number of rows
Size of array(atTopics{17}) returns 50, which the number of columns for the 17th row

In the following example, a pointer to each field of each table in the database is stored in a two-dimensional array:

 C_LONGINT($vlLastTable;$vlLastField)

 C_LONGINT($vlFieldNumber)

  ` Create as many rows (empty and without columns) as there are tables

 $vlLastTable:=Get last table number

 ARRAY POINTER(<>apFields;$vlLastTable;0) `2D array with X rows and zero columns

  ` For each table

 For($vlTable;1;$vlLastTable)

    If(Is table number valid($vlTable))

       $vlLastField:=Get last field number($vlTable)

  ` Give value of elements

       $vlColumnNumber:=0

       For($vlField;1;$vlLastField)

          If(Is field number valid($vlTable;$vlField))

             $vlColumnNumber:=$vlColumnNumber+1

  `Insert a column in a row of the table underway

             INSERT IN ARRAY(<>apFields{$vlTable};$vlColumnNumber;1)

  `Assign the "cell" with the pointer

             <>apFields{$vlTable}{$vlColumnNumber}:=Field($vlTable;$vlField)

          End if

       End for

    End if

 End for

Provided that this two-dimensional array has been initialized, you can obtain the pointers to the fields for a particular table in the following way:

  ` Get the pointers to the fields for the table currently displayed at the screen:

 COPY ARRAY(◊apFields{Table(Current form table)};$apTheFieldsIamWorkingOn)

  ` Initialize Boolean and Date fields

 For($vlElem;1;Size of array($apTheFieldsIamWorkingOn))

    Case of

       :(Type($apTheFieldsIamWorkingOn{$vlElem}->)=Is date)

          $apTheFieldsIamWorkingOn{$vlElem}->:=Current date

       :(Type($apTheFieldsIamWorkingOn{$vlElem}->)=Is Boolean)

          $apTheFieldsIamWorkingOn{$vlElem}->:=True

    End case

 End for

Note: As this example suggests, rows of a two-dimensional arrays can be the same size or different sizes.