Mapping of Simple Types
In general, the OpenOffice.org Basic type system is not rigid. Unlike C++ and Java, OpenOffice.org Basic does not require the declaration of variables, unless the Option Explicit
command is used that forces the declaration. To declare variables, the Dim
command is used. Also, a OpenOffice.org Basic type can be optionally specified through the Dim
command. The general syntax is:
Dim VarName [As Type][, VarName [As Type]]...
All variables declared without a specific type have the type Variant
. Variables of type Variant
can be assigned values of arbitrary Basic types. Undeclared variables are Variant
unless type postfixes are used with their names. Postfixes can be used in Dim
commands as well. The following table contains a complete list of types supported by Basic and their corresponding postfixes:
Type | Postfix | Range |
---|---|---|
Boolean | True or False | |
Integer | % | -32768 to 32767 |
Long | & | -2147483648 to 2147483647 |
Single | ! | Floating point number
negative: -3.402823E38 to -1.401298E-45 positive: 1.401298E-45 to 3.402823E38 |
Double | # | Double precision floating point number
negative: -1.79769313486232E308 to -4.94065645841247E-324 positive: 4.94065645841247E-324 to 1.79769313486232E308 |
Currency | @ | Fixed point number with four decimal places
-922,337,203,685,477.5808 to 922,337,203,685,477.5807 |
Date | 01/01/100 to 12/31/9999 | |
Object | Basic Object | |
String | $ | Character string |
Variant | arbitrary Basic type |
Consider the following Dim examples.
Dim a, b ' Type of a and b is Variant Dim c as Variant ' Type of c is Variant Dim d as Integer ' Type of d is Integer (16 bit!) ' The type only refers to the preceding variable Dim e, f as Double ' ATTENTION! Type of e is Variant! ' Only the type of f is Double Dim g as String ' Type of g is String Dim h as Date ' Type of h is Date ' Usage of Postfixes Dim i% ' is the same as Dim i as Integer Dim d# ' is the same as Dim d as Double Dim s$ ' is the same as Dim s as String
The correlation below is used to map types from UNO to Basic and vice versa.
UNO | Basic |
---|---|
void | internal type |
boolean | Boolean |
byte | Integer |
short | Integer |
unsigned short | internal type |
long | Long |
unsigned long | internal type |
hyper | internal type |
unsigned hyper | internal type |
float | Single |
double | Double |
char | internal type |
string | String |
type | com.sun.star.reflection.XIdlClass |
any | Variant |
The simple UNO type type is mapped to the com.sun.star.reflection.XIdlClass interface to retrieve type specific information. For further details, refer to UNO Reflection API.
When UNO methods or properties are accessed, and the target UNO type is known, Basic automatically chooses the appropriate types:
' The UNO object oExample1 has a property "Count" of type short a% = 42 oExample1.Count = a% ' a% has the right type (Integer) pi = 3,141593 oExample1.Count = pi ' pi will be converted to short, so Count will become 3 s$ = "111" oExample1.Count = s$ ' s$ will be converted to short, so Count will become 111
Occasionally, OpenOffice.org Basic does not know the required target type, especially if a parameter of an interface method or a property has the type any
. In this situation, OpenOffice.org Basic mechanically converts the OpenOffice.org Basic type into the UNO type shown in the table above, although a different type may be expected. The only mechanism provided by OpenOffice.org Basic is an automatic downcast of numeric values:
Long and Integer values are always converted to the shortest possible integer type:
- to
byte
if -128 <= Value <= 127 - to
short
if -32768 <= Value <= 32767
The Single/Double
values are converted to integers in the same manner if they have no decimal places.
This mechanism is used, because some internal C++ tools used to implement UNO functionality in OpenOffice.org provide an automatic upcast but no downcast. Therefore, it can be successful to pass a byte
value to an interface expecting a long
value, but not vice versa.
In the following example, oNameCont
is an object that supports com.sun.star.container.XNameContainer and contains elements of type short
. Assume FirstValue
is a valid entry.
a% = 42 oNameCount.replaceByName( "FirstValue", a% ) ' Ok, a% is downcasted to type byte b% = 123456 oNameCount.replaceByName( "FirstValue", b% ) ' Fails, b% is outside the short range
The method call fails, therefore the implementation should throw the appropriate exception that is converted to a OpenOffice.org Basic error by the OpenOffice.org Basic RTL. It may happen that an implementation also accepts unsuitable types and does not throw an exception. Ensure that the values used are suitable for their UNO target by using numeric values that do not exceed the target range or converting them to the correct Basic type before applying them to UNO.
Always use the type Variant
to declare variables for UNO Basic objects, not the type Object
. The OpenOffice.org Basic type Object
is tailored for pure OpenOffice.org Basic objects and not for UNO OpenOffice.org Basic objects. The Variant
variables are best for UNO Basic objects to avoid problems that can result from the OpenOffice.org Basic specific behavior of the type Object
:
Dim oService1 ' Ok oService1 = CreateUnoService( "com.sun.star.anywhere.Something" ) Dim oService2 as Object ' NOT recommended oService2 = CreateUnoService( "com.sun.star.anywhere.SomethingElse" )
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