Using Procedures, Functions or Properties

Contents

# Using Procedures, Functions and Properties

The following describes the basic use of procedures, functions and properties in LibreOffice Basic.

When you create a new module, LibreOffice Basic automatically inserts a Sub called "Main". This default name has nothing to do with the order or the starting point of a LibreOffice Basic project. You can also safely rename this Subroutine.

Some restrictions apply for the names of your public variables, subroutines, functions and properties. You must not use the same name as one of the modules of the same library.

Procedures (Subroutines) functions (Function) and properties (Property) help you maintaining a structured overview by separating a program into logical pieces. These pieces can be easily reused to perform similar tasks in other projects.

## Passing Variables to Procedures, Functions or Properties

Variables can be passed to both procedures, functions or properties. The Sub Function or Property must be declared to expect parameters:

      Sub SubName(Parameter1 As TYPENAME, Parameter2 As TYPENAME,...)
          ' your code goes here
      End Sub

The Sub is called using the following syntax:

      [Call] SubName( [Parameter1:=]Value1, [Parameter2:=]Value2, ...)

The parameters passed to a Sub must fit to those specified in the Sub declaration.

The same process applies to a Function. In addition, functions always return a result. This result is defined by assigning the value to return to the function name:

      Function FunctionName(Parameter1 As TYPENAME, Parameter2 As TYPENAME,...) As TYPENAME
          ' your code goes here
          FunctionName=Result
      End Function

The Function is called using the following syntax:

      Variable = FunctionName( [Parameter1:=]Value1, [Parameter2:=]Value2, ...)

Properties combine the syntax of procedures and functions. A Property usually requires up to one parameter.

      Private _IsApproved As TYPENAME
      Property Get IsApproved As TYPENAME
          ' your code goes here
          IsApproved = some_computation
      End Property
      Property Let IsApproved(value As TYPENAME)
          ' your code goes here
          _IsApproved = computed_value
      End Property

The Property is called using the following syntax:

      var = IsApproved
      IsApproved = some_value

You can also use the fully qualified name to call a procedure, function or property:
[Call] Library.Module.Macro(), where Call is optional.
For example, to call the Autotext macro from the Gimmicks library, use the following command:
Gimmicks.AutoText.Main()

## Passing Variables by Value or Reference

Parameters can be passed to a procedure, a function or a property either by reference or by value. Unless otherwise specified, a parameter is always passed by reference. That means that a Sub, a Function or a Property gets the parameter and can read and modify its value.

If you want to pass a parameter by value insert the key word ByVal in front of the parameter when you call a Sub, a Function or a Property, for example:

      Function ReadOnlyParms(ByVal p2, ByVal p2)
          ' your code goes here
      End Function
      result = ReadOnlyParms(parm1, parm2)

In this case, the original content of the parameter will not be modified by the Function since it only gets the value and not the parameter itself.

## Defining Optional Parameters

Functions, procedures or properties can be defined with optional parameters, for example:

      Sub Rounding(number, Optional decimals, Optional format)
          ' your code goes here
      End Sub

## Positional or Keyword Arguments

When you call a function or a subroutine, you may pass its arguments by position or by name. Passing by position means just listing the arguments in the order in which the parameters are defined in the function or subroutine. Passing by name requires you to prefix the argument with the name of the corresponding parameter followed by a colon and an equal sign (:=). Keyword arguments may appear in any order. Refer to Basic Replace() function for such examples.

When needing to pass less parameters, use keywords arguments. Passing values for fewer parameters by position requires to supply values for all parameters before them, optional or not. This ensures that the values are in the correct positions. If you pass the parameters by name - using keyword arguments - you may omit all other intermediate arguments.

## Scope of Variables

A variable defined within a Sub, a Function or a Property, only remains valid until the procedure is exited. This is known as a "local" variable. In many cases, you need a variable to be valid in all procedures, in every module of all libraries, or after a Sub, a Function or a Property is exited.

### Declaring Variables Outside a Sub a Function or a Property

    Global VarName As TYPENAME

The variable is valid as long as the LibreOffice session lasts.

    Public VarName As TYPENAME

The variable is valid in all modules.

    Private VarName As TYPENAME

The variable is only valid in this module.

    Dim VarName As TYPENAME

The variable is only valid in this module.

### Example for private variables

Enforce private variables to be private across modules by setting CompatibilityMode(True).

      ' ***** Module1 *****
      Private myText As String
      Sub initMyText
          myText = "Hello"
          Print "In module1 : ", myText
      End Sub

      ' ***** Module2 *****
      'Option Explicit
      Sub demoBug
          CompatibilityMode( True )
          initMyText
          ' Now returns empty string
          ' (or raises error for Option Explicit)
          Print "Now in module2 : ", myText
      End Sub

### Saving Variable Content after Exiting a Sub a Function or a Property

      Static VarName As TYPENAME

The variable retains its value until the next time the a Function, Sub or Property is entered. The declaration must exist inside a Sub, a Function or a Property.

## Specifying the Return Value Type of a Function or a Property

As with variables, include a type-declaration character after the function name, or the type indicated by As and the corresponding data type at the end of the parameter list to define the type of the function or property's return value, for example:

      Function WordCount(WordText As String) As Integer

Related Topics

CompatibilityMode() Function

Option Explicit Statement

Optional keyword

Property Statement

Static Statement

Please support us!