Miscellaneous Datatypes

Datatypes miscellaneous

What are the initial values of variables in TD

All variables in TD are initially set to a specific value.
For instance, a local Number variable within a function is automatically initialized with value = 0 (zero).

Here the list of base datatypes and their initial values:

Binary	BINARY_Null
Boolean	FALSE (0)
DateTime	DATETIME_Null
File Handle	hWndNULL
Long String	STRING_Null ("")
Number	0
Session Handle	hWndNULL
Sql Handle	hWndNULL
String	STRING_Null ("")
Window Handle	hWndNULL
UDV	!= OBJ_Null

As for objects/UDV's (instances of functional classes):
An object and all it's attributes (class variables/Instance variables) are initialized using the table above.
Though, you can initialize an object to OBJ_Null (starting from CTD 2.0) by assigning OBJ_Null at the declaration:

   ♦ Variables
      cfcTest: uMyUDV = OBJ_Null

How to get dynamically the type of a variable

At runtime, the function SalCompileAndEvaluate can be used to determine the type of a variable.

Set nType = SalCompileAndEvaluate( sExpression, nError, nErrorPos, nReturn, sReturn, dtReturn, hWndReturn, FALSE, sContext )
If nType = EVAL_Number
   ! Variable is a Number
Else If nType = EVAL_String
   ! Variable is a String
Else if ntype = EVAL_Date
   ! Variable is a DateTime
Else If nType = EVAL_Handle
   ! Variable is a Handle (window, Sql, File)
ELse If nType = EVAL_Template
   ! sExpression is a template, class
Else If nType = 7
   ! Variable is an object (UDV). This nType seems to be undocumented

Example

Set nType = SalCompileAndEvaluate( "strTest", nError, nErrorPos, nReturn, sReturn, dtReturn, hWndReturn, FALSE, sContext )
Set nType = SalCompileAndEvaluate( "udvCustomer", nError, nErrorPos, nReturn, sReturn, dtReturn, hWndReturn, FALSE, sContext )

The sContext parameter should be the context handle where the variable resides in.
So if the variable is declared in the current context (where the SalCompileAndEvaluate is called) use

  sContext = SalContextCurrent( )