We all know DataFlex is a great product to build database applications, most of the data will be entered by end-users and printed or otherwise processed. But what if you need to import data from other manufacturers? What do we have to do?

Sequential I/O commands
When we want to read data in a DataFlex application we can make a choice between the commands Read, ReadLn, Read_Block and Read_Hex. Of course before you can read the input stream (usually a file) needs to be opened...

When your Visual DataFlex application makes an external call to a webservice the main program waits for its completion. If the request does not return immediately several things can be the cause. Your connection to your ISP can slow, the webserver you try to reach is busy, can be difficult found etc. If you want your application to continue as soon as possible and know (and this is they unknown keyfactor) that particular call should not take more than a couple of milliseconds to complete you can...

UAC, short for User Access Control, the feature built in Microsoft Windows Vista and higher is turned off by a number of users and developers because they do not like that the operating system asks for permission to write or access certain areas of their environment. Building your applications you are however advised not to do this because sooner or later you will install your not UAC compliant application at a UAC controlled PC and that is not goo.

How can you find out if UAC is...

The new Visual DataFlex grid classes in Visual DataFlex 16.0 (cCJGrid, cDbCJGrid, etc) do not expose an interface for setting the grid control's various Fonts. This turned out to be beyond the scope for the VDF 16.0 project, however it is still possible to set all of the control's fonts via the COM interface.

For example here is how you can modify the default Font used to display data in the Grid's cells: You would write the following event handler in your grid object...
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The other day I received an interesting question from a developer about argument_size and web services. Specifically he wanted to create a web service in VDF that accepts a file attachment along with some other metadata for the file. It would look something like this (actual code modified for brevity):

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We're continuing the back to the basics theme for advanced VDF developers by visiting the other side of External_Function. If you haven't done so already, you should read the first part, it's a prerequisite for understanding what I'm about to talk about here.

Let's start with a simple DLL written in C++, exporting only one silly function SayHello(), which we'll call from our VDF program. The finished C++ project is attached at the end of this article, but we'll take it step by step....

The information about row and column changing is still being documented. There are significant changes in the way the new grid works as compared to the old grids. Here is a summary that should help everyone get started.

Navigation consists of changing columns and changing rows. A navigation event consists of a row change and/or a column change. It is best to think of these as two events.

Column Change

When a column change occurs, events are sent to the...

Frank is asking about a peculiar behavior with numeric masks and rounding, where it seemingly sometimes rounds the value to the specified number of decimals in the mask, but other times it seems to truncate instead. What's going on? Is this a bug?

Frank demonstrated the problem in an excellent manner using a tiny program like this:
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When using one of the database Connectivity Kits, how can you make your program display its own error message when a connection string is not correct? By default, an error is displayed and the database will pop up a login dialog for users to enter their correct user and password. Or the application may display an unhandled error. Hmm... not what you want to see when using either the login command or SQLConnect method.


In order to have your application better handle those errors,...

Recent research has suggested that "devil" is actually an old fashioned spelling for "developer". While this does not entirely surprise me, I will leave the theological implication of this to others. What I would like to discuss is how this applies to the old adage "Idle hands are the devil’s workshop". Does this really refer to developers and, if so, how can we make idle hands or, more accurately idle handlers part of our workshop?

In Visual DataFlex...

Let's take a closer look at External_Function. But first, there are currently two generic and well established technologies you can use from VDF to interact with external components, DLL functions and COM objects. Actually, there are several other techniques available as well, the obsolete and defunct DDE technology, and the more modern SOAP technology for example, and various other IPC mechanisms. But we'll ignore those for now.

DLL and COM are the two fundamental technologies for...

Source Control has been discussed in our forums off and on for years and it appears that some developers are not convinced that using it will benefit them. If you are not currently using source control, you should seriously reconsider doing so. I hope this article clears up most questions you have.

Source control is often also referred to as "version control" or "revision control". I prefer the term source control because it does so much more than simply tracking...

In the last article I mentioned that the Address type can be used to efficiently copy a Char[] containing a null terminated C string to a VDF String, and I also mentioned that it works the other way around. A follow-up question I received (and should have predicted) was about exactly how you can do that.

Basically, the task is to quickly and efficiently copy a VDF String to a Char[]. The first solution one might come up with is to loop through the characters in the string and assign...

If you've been a VDF developer for a while you've undoubtedly come across Pointer, but what about the Address type? Isn't that just redundant?

Pointer has been around seemingly forever, but you may or may not know that Pointer is not a real data type in its own right. If you type Pointer in the Visual DataFlex Studio editor and hover your mouse cursor over the word, you'll see a tooltip that says "Alias type Pointer Integer". So even though it's been around for so long,...

In order to update our Samples to use the new XML methods (*NS methods) and schema validation, I had to go through some steps to get it all working. I thought it would be beneficial to document what I have done and share what I have learned while converting the samples -- so here I am.

Note that these changes are not required for applications to be migrated to Visual DataFlex 15.1, but namespaces can play a vital role in a data integration project or data exchange scenario, where...

When it comes to performance working in the Studio as a developer, as opposed to running the application, there are generally two performance critical areas. The first one is the Studio Parser, which is the foundation for CodeSense, Visual Modeling, Go-To-Definition and more. The second performance critical area is when compiling. Unnecessarily long and slow compile times can make for a very frustrating experience working with the Visual DataFlex Studio.

Sometimes you may not even...

A while ago I received a question about why the following code is not working as expected:

It's a little tricky, but the code is expecting a pointer to a null terminated C-style string. And usually AddressOf() will produce that with a local string variable. But in this case AddressOf() actually returns a pointer to the iIndex'th element...

Our forums are chock full of information and we want to make sure that everyone can make the most of this.

Post all relevant information

Sometimes the operating system on which you encounter a problem matters, sometimes it does not, sometimes other product versions matter. By providing all the pertinent information from the get-go, it allows people who read your posts to better help you and not have to guess. At minimum, I would suggest that you provide the following...

A big part of our job as software developers is knowing lots of detailed information, but I would argue that knowing how to find information when you need it is even more important. So here is an assortment of resources and tips for Visual DataFlex developers. I use just about all of these resources on a daily basis:

• The DAW Development Team blog (you're reading it now )
• The DAW Forums: Peer to peer support for developers.
• DAW Knowledge Base (KBase): Technical articles with solutions

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A well known old trick in DataFlex is the Move 0 to Recnum trick. It's been used with character mode DataFlex and Visual DataFlex for so long that nobody probably remembers where it came from, and I'm not sure it was ever really a documented or intended feature in the beginning. Nonetheless it became a fully supported technique at some point.

Basically, if you ever wanted to create a new record loosely based on data from an existing record, you could use this trick to simplify code...