4th Dimension (software)

Architecture

A 4D application can run in either Standalone mode or Client-Server mode.

Single-User

In Standalone mode, the 4D application (4D.exe on Windows or 4D.app on Mac) is used to open the structure file (4DB/4DC) file directly along with the associated data file (4DD).

Client-Server

In the Client-Server paradigm the 4D Server application (4DServer.exe on Windows or 4DServer.app on Mac) is used to open the structure file (4DB/4DC) file directly along with the associated data file (4DD). 4D may then be used in remote mode to connect to the 4D Server.

Application Editions

4D has two applications; 4D and 4D Server. 4D Server runs only as a server but 4D can be run in either standalone or remote mode.

4D

4D can be run in two modes. 4D in single-user mode allows for 1 person to run the application. 4D in remote mode is used for connecting to a 4D Server.

4D Server

4D Server is used for Client-Server connectivity to the application. In this mode, 4D Server loads the structure file (4DB or 4DC) and also the datafile (4DD) and provides network access to 4D (in remote). Each workstation has a dynamically updated cache of the resources they are working with, while the 4D Server maintains the data and code.

Syntax

This section will include syntax examples, demonstrating different programming constructs used in 4D, such as for loops and variable usage.

Data Types

4D fields, variables, and expressions can be of the following data types:

More info on 4D data type can be found on the [ 4D Data Types] documentation page

Variable Scope

Local variables are prefixed with a $ like $myLocalVariable and only live for the duration of the method.

Process variables have no prefix like myProcessVariable and live throughout the duration of the process.

Inter-process (or Global) variables are prefixed with a <> like <>myGlobalVariable and live throughout the duration of the application.

Comparison of looping

For

For(vCounter;1;100) // Do something End for

While

$i :=1 // Initialize the counter While($i<=100) // Loop 100 times // Do something $i :=$i +1 // Need to increment the counter End while

Repeat

$i :=1 // Initialize the counter Repeat // Do something $i :=$i +1 // Need to increment the counter Until($i=100) // Loop 100 times

Nested Loops

The following example goes through all the elements of a two-dimensional array:

For($vlElem;1;Size of array(anArray)) // ... // Do something with the row // ... For($vlSubElem;1;Size of array(anArray{$vlElem})) // Do something with the element anArray{$vlElem}{$vlSubElem}:=... End for End for

The following example builds an array of pointers to all the date fields present in the database:

ARRAY POINTER($apDateFields;0) $vlElem:=0 For($vlTable;1;Get last table number) // loop over each table number with $vTable as the number If(Is table number valid($vlTable)) // check if table number $vTable is valid // only loop on the valid table For($vlField;1;Get last field number($vlTable)) // loop over each field number within current table // with $vlField as the current field number If(Is field number valid($vlTable;$vlField)) // check if field number is valid $vpField:=Field($vlTable;$vlField) // get pointer to field If(Type($vpField->)=Is date) // check if current field is a date // only performs these actions if field is a date $vlElem:=$vlElem+1 INSERT IN ARRAY($apDateFields;$vlElem) $apDateFields{$vlElem}:=$vpField End if End If End for End If End for