The LA Fox Developer Newsletter

April 2000

ADO Jumpstart (Con't from page 3)

Converting a hex value to decimal in Visual FoxPro is simple.

The following code illustrate how to convert hexadecimal values

to decimal:

x = 0x00000080

?x && 128

And, if you ever need to convert back to hexadecimal:

?Transform(128,”@O”) && 0x00000080

Using our original hex value, 11101010, and working from right to

left and beginning with zero, see that the seventh bit is set.

Therefore, the seventh bit of the Attributes property, if set,

means the field is long. Going further, whatever attributes

occupy bits 1, 3, 5, and 6, also apply to this field. The following

table of field attributes should help to sort things out:

Table 4. Field Attributes

So, along with being a long field, the field is deferred,

updateable, can have a null written to it, and it may also already

contain a null value. Visually, this makes sense. How can you

do this programmatically?

If you refer to online examples(almost always programmed in

Visual Basic) you will see code like this:

If (oFieId.Attribute AND adFldLong) = adFldLong

The field is long

End If

This is pretty slick in that you can test for whether a specific

attribute bit is set by using the AND operator with the attribute

property and the constant. If you try this in Visual FoxPro, you

will get data type mismatch errors. Fortunately, there is a way.

Visual FoxPro contains a host of bit functions. One function,

BITTEST, does as its name implies. It tests whether a specified

bit in a passed argument is set. To review, we need to see if the

seventh bit in the value 234 is set. The following Visual FoxPro

code demonstrates how to use the BITTEST function:

If BitTest(234,7)

*~ The Field is long

Endif

To find out if the field is nullable:

If BltTest(234,5)

*/ The Field is long

Endif

The Attributes property of the Connection, Parameter, and

Property objects works in the same manner as illustrated

above. The differences are the names and quantity of attributes

that are present.

ADO and COM Defined Constants

ADO and OLE DB, like any COM components, make extensive

use of defined constants in the examples that document the

usage of properties, events, and methods. Other development

environments in Visual Studio such as Visual Basic and Visual

lnterdev provide lntelliSense technology, because of their

respective abilities to interact directly with the type libraries of

COM components. For these development environments, you

can reference defined constants just as if they were a part of the

native language. So, working with published examples is a fairly

trivial task. On the other hand, in the Visual FoxPro develop-

ment environment there is, in fact, a bit of a challenge. The

question always seems to be “How can I use the Visual Basic

samples in Visual FoxPro?” The biggest stumbling block is

usually in finding the value of the defined constants. In Visual

FoxPro, you need to use the #Define statement for each

constant.

One solution for obtaining the value of the ADO defined con-

stants is to obtain the MDAC SDK from Microsoft. The MDAC

SDK can be downloaded from http://www.microsoft.com/data/

mdac2.htm.

Once you install the SDK, locate the Include\ADO directory. In

that directory, you will find the ADOINT.H file, which contains all

of the enumerated types and the values for the defined con-

stants.

A second, and perhaps easier, solution is to use the resources

already installed on your machine. If you are working through

the sample code in this paper, you already have the Microsoft

Data Access Components installed on your workstation. The

Visual Basic Development Environment (both the full Visual

Basic IDE and the Visual Basic Editor in desktop applications

like Word and Excel) has a great resource called the Object

Browser. This could, in fact, be the most underutilized tool on

the planet.

To illustrate its functionality, open any desktop application that

uses Visual Basic, such as Word or Excel. Or, if you have the

Visual Basic Programming System installed, you can open that

(Con't, page 5)

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