Difference between revisions of "Arrays"

Revision as of 08:36, 5 July 2013

This page covers Arrays from any datatype tips & tricks.

Passing arrays in messages (any datatypes)

^{(From CenturaPro september 1999)}
To pass arrays using messages, use this nice trick to convert the address of any type of array
to a number and send them along as wParam or lParam.

At the source (sending side) do this to pass arrays to a window

   ! Construct an array with weekdays
   Set saWeekDay[0] = "Monday"
   Set saWeekDay[1] = "Tuesday"
   Set saWeekDay[2] = "Wednesday"
   !
   ! Construct an array with customer objects
   Set uaCustomer[0].sivCustomerName = "Brendan Perry"
   Set uaCustomer[0].nivCustomerID = 1
   Set uaCustomer[1].sivCustomerName = "Lisa Gerrard"
   Set uaCustomer[1].nivCustomerID = 2
   !
   ! Get the address of the arrays as number
   Set nAddressStringArray = SalWindowHandleToNumber( saWeekDay )
   Set nAddressUDVArray = SalWindowHandleToNumber( uaCustomer )
   !
   ! Send along the addresses as wParam and lParam
   Call SalPostMsg( frmMain, SAM_User, nAddressStringArray, nAddressUDVArray )

Now at the receiving side (frmMain), convert the array address back to an array variable

   On SAM_User
      Call VisArrayCopy( SalNumberToWindowHandle( wParam ), saWeekDay, DT_String )
      Call VisArrayCopy( SalNumberToWindowHandle( lParam ), uaCustomer, DT_Handle )

Here you can download a sample:

• WIKI_PassingArraysInMessages.zip
  

Single function to get number of elements in any array

Having an array (any type) the following piece of code will determine how many elements are in the array:

   Local variables
      String: saMyArray[*]
   Actions
      ...
      If SalArrayIsEmpty( saMyArray )
         Set nArrayCount = 0
      Else
         Call SalArrayGetUpperBound( saMyArray, 1, nUpperBound )
         Set nArrayCount = nUpperBound + 1
      ...

This is a tedious task when you need to get the number elements spread over your sourcecode.
The code above does not even take into account the use of a different lower bound of the array (so not starting at zero index).
It would be simpler having a single function to do this, for any array you pass to it.

   Local variables
      String: saMyArray[*]
      Number: naMyArray[1:*]
      Customer: uaMyCustomerArray[*,5]
      Number: nArrayCount
   Actions
      ...
      Set nArrayCount = PALArrayGetCount( saMyArray )    ! string array count
      Set nArrayCount = PALArrayGetCount( naMyArray )    ! number array count
      Set nArrayCount = PALArrayGetCount( uaMyCustomerArray )    ! object array count
      ...

Problem is you can have arrays of any type: strings, numbers, datetimes,objects etc.

So creating a function in which you pass any array, you need to specify the correct datatype of the parameter.
That would mean multiple functions, each predefined for a specific datatype. And this is not very convenient.

But we can use a trick which works for all datatypes and works on all TD versions (tested up to TD 6.2).

It is secretly known that the TD compiler accepts passing an array to a function which accepts it as Window Handle datatype.
Also the Sal/Vis functions on arrays (like SalArrayGetUpperBound) accept Window Handle datatype to reflect the array.

Have a look at this:

Function: TestArray
    Local variables
        String: saTest[*]
    Actions
        Call ArrayFunction( saTest )

Function: ArrayFunction
    Parameters
        Window Handle: phWndArray[*]
    Local variables
        Number: nUpperBound
    Actions
        Call SalArrayGetUpperBound( phWndArray, 1, nUpperBound )
        ...

As can be seen, the ArrayFunction has a Window Handle array as parameter.
The TestArray function passes a string array to the ArrayFunction.
The compiler accepts this and also the passed array is treated as an array correctly.

BEWARE: maybe you have seen such a trick before, but it could be that the parameter is defined as Window Handle and not as a Window Handle array.
With TD 6.1 and up, the compiler does NOT accept a Window Handle parameter like "Window Handle: phWndArray", you must define it as a real array
like this: Window Handle: phWndArray[*]. Mind the brackets.

ANOTHER BEWARE: this trick does NOT work on .NET projects. The .NET compiler strictly forbids casting datatypes.

Using this "feature", a simple function can be created which is able to get the number of elements of ANY array.

The sample has two globally defined functions:

    PALArrayGetCount( Array ) -> gets the number of elements in Array for the first dimension only
    PALArrayDimGetCount( Array, nDimension ) -> gets the number of elements in Array for any dimension (1..n)

Here you can download the sample using these two functions:

• WIKI_PALArrayGetCount.zip