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BASIC Guide

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• The Language of OpenOffice.org Basic

• Overview of a Basic Program
• Working With Variables
• Strings
• Numbers
• Boolean Values
• Date and Time
• Arrays
• Scope and Life Span of Variables
• Constants
• Operators
• Branching
• Loops
• Procedures and Functions
• Error Handling
• Other Instructions

• Runtime Library

• Conversion Functions
• Strings
• Date and Time
• Files and Directories
• Message and Input Boxes
• Other Functions

• Introduction to the API

• Universal Network Objects (UNO)
• Properties and Methods
• Modules, Services and Interfaces
• Tools for Working with UNO
• Overview of Central Interfaces

• Working with Documents

• The StarDesktop
• Styles and Templates

• Text Documents

• The Structure of Text Documents
• Editing Text Documents
• More than Just Text

• Spreadsheet Documents

• The Structure of Spreadsheets
  • Rows and Columns
  • Cells and Ranges
  • Formatting Spreadsheet Documents
• Editing Spreadsheet Documents

• Drawings and Presentations

• The Structure of Drawings
• Editing Drawing Objects
• Presentations

• Charts (Diagrams)

• Using Charts in Spreadsheets
• The Structure of Charts
• Chart Types

• Databases

• SQL: a Query Language
• Types of Database Access
• Data Sources
• Database Access

• Dialogs

• Working With Dialogs
• Properties
• Events
• Dialog Control Elements

• Forms

• Working With Forms
• Control Element Forms
• Database Forms

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Working with Sets of Characters

When administering strings, OpenOffice.org Basic uses the set of Unicode characters. The Asc and Chr functions allow the Unicode value belonging to a character to be established and/or the corresponding character to be found for a Unicode value. The following expressions assign the various Unicode values to the code variable:

Code = Asc("A")         ' Latin letter A (Unicode-value 65)
Code = Asc("€")         ' Euro character (Unicode-value 8364)
Code = Asc("Л")         ' Cyrillic letter Л (Unicode-value 1083)

Conversely, the expression

MyString = Chr(13)

ensures that the MyString string is initialized with the value of the number 13, which stands for a hard line break.

The Chr command is often used in Basic languages to insert control characters in a string. The assignment

MyString = Chr(9) + "This is a test" + Chr(13)

therefore ensures that the text is preceded by a tab character (Unicode-value 9) and that a hard line break (Unicode-value 13) is added after the text.

Accessing Parts of a String

OpenOffice.org Basic provides three functions that return partial strings, plus a length function:

Left(MyString, Length)

returns the first Length characters of MyString.

Right(MyString, Length)

returns the last Length characters of MyString.

Mid(MyString, Start, Length)

returns first Length characters of MyString as of the Start position.

Len(MyString)

returns the number of characters in MyString.

Here are a few example calls for the named functions:

Dim MyString As String
Dim MyResult As String
Dim MyLen As Integer

MyString = "This is a small test"
MyResult = Left(MyString,5)      ' Provides the string "This "
MyResult = Right(MyString, 5)    ' Provides the string " test"
MyResult = Mid(MyString, 8, 5)   ' Provides the string " a sm"
MyLen = Len(MyString)            ' Provides the value 20

Search and Replace

OpenOffice.org Basic provides the InStr function for searching for a partial string within another string:

ResultString = InStr (MyString, SearchString)

The SearchString parameter specifies the string to be searched for within MyString. The function returns a number that contains the position at which the SearchString first appears within MyString; a return value of zero indicates no match. If you want to find other matches for the string, the function also provides the opportunity to specify an optional start position from which OpenOffice.org Basic begins the search. In this case, the syntax of the function is:

ResultString = InStr(StartPosition, MyString, SearchString)

In the previous examples, InStr ignores uppercase and lowercase characters. To change the search so that InStr is case sensitive, add the parameter 0, as shown in the following example:

ResultString = InStr(MyString, SearchString, 0)

Using the previous functions for editing strings, programmers can search for and replace one string in another string:

Function Replace(Source As String, Search As String, NewPart As String)
  Dim Result As String
  Dim StartPos As Long
  Dim CurrentPos As Long

  Result = ""
  StartPos = 1
  CurrentPos = 1

  If Search = "" Then
    Result = Source
  Else 
    Do While CurrentPos <> 0
      CurrentPos = InStr(StartPos, Source, Search)
      If CurrentPos <> 0 Then
        Result = Result + Mid(Source, StartPos, _
        CurrentPos - StartPos)
        Result = Result + NewPart
        StartPos = CurrentPos + Len(Search)
      Else
        Result = Result + Mid(Source, StartPos, Len(Source))
      End If                ' Position <> 0
    Loop 
  End If 

  Replace = Result
End Function

The function searches through the transferred Search string in a loop by means of InStr in the original term Source. If it finds the search term, it takes the part before the expression and writes it to the Result return buffer. It adds the NewPart section at the point of the search term Search. If no more matches are found for the search term, the function establishes the part of the string still remaining and adds this to the return buffer. It returns the string produced in this way as the result of the replacement process.

Since replacing parts of character sequences is one of the most frequently used functions, the Mid function in OpenOffice.org Basic has been extended so that this task is performed automatically. The following example replaces three characters with the string is from the sixth position of the MyString string.

Dim MyString As String
 
MyString = "This was my text"
Mid(MyString, 6, 3, "is")

When it is used with 4 arguments, to replace a sub-string in a string, Mid is an instruction, not a function : it does not return any value !

Formatting Strings

The Format function formats numbers as a string. To do this, the function expects a Format expression to be specified, which is then used as the template for formatting the numbers. Each place holder within the template ensures that this item is formatted correspondingly in the output value. The five most important place holders within a template are the zero (0), pound sign (#), period (.), comma (,) and dollar sign ($) characters.

The 0 character within the template ensures that a number is always placed at the corresponding point. If a number is not provided, 0 is displayed in its place.

A . stands for the decimal point symbol defined by the operating system in the country-specific settings.

The example below shows how the 0 and . characters can define the digits after the decimal point in an expression:

MyFormat = "0.00"
MyString = Format(-1579.8, MyFormat)     ' Provides "-1579,80"
MyString = Format(1579.8, MyFormat)      ' Provides "1579,80"
MyString = Format(0.4, MyFormat)         ' Provides "0,40"
MyString = Format(0.434, MyFormat)       ' Provides "0,43"

In the same way, zeros can be added in front of a number to achieve the desired length:

MyFormat = "0000.00"
MyString = Format(-1579.8, MyFormat)     ' Provides "-1579,80"
MyString = Format(1579.8, MyFormat)      ' Provides "1579,80"
MyString = Format(0.4, MyFormat)         ' Provides "0000,40"
MyString = Format(0.434, MyFormat)       ' Provides "0000,43"

A , represents the character that the operating system uses for a thousands separator, and the # stands for a digit or place that is only displayed if it is required by the input string.

MyFormat = "#,##0.00"
MyString = Format(-1579.8, MyFormat)     ' Provides "-1.579,80"
MyString = Format(1579.8, MyFormat)      ' Provides "1.579,80"
MyString = Format(0.4, MyFormat)         ' Provides "0,40"
MyString = Format(0.434, MyFormat)       ' Provides "0,43"

In place of the $ place holder, the Format function displays the relevant currency symbol defined by the system (this example assumes a European locale has been defined):

MyFormat = "#,##0.00 $"   
MyString = Format(-1579.8, MyFormat)     ' Provides "-1.579,80 €" 
MyString = Format(1579.8, MyFormat)      ' Provides "1.579,80 €" 
MyString = Format(0.4, MyFormat)         ' Provides "0,40 €" 
MyString = Format(0.434, MyFormat)       ' Provides "0,43 €"

The format instructions used in VBA for formatting date and time details can also be used:

sub main
    dim myDate as date
    myDate = "01/06/98"
    TestStr = Format(myDate, "mm-dd-yyyy") ' 01-06-1998
    MsgBox TestStr
end sub

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