How to use Labview 6 to call OpenPrinter()

I would like to use Labview 6.0.2 to call API winspool.drv function OpenPrinter().

[email protected] wrote:
Thanks for your help, but I had already tried the steps you suggested. The OpenPrinter() function takes two input parameters: one is the printer name, the other parameter the printer defaults with its type of data as structure in C, which is equivelent to the data type of cluster in Labview. The only output parameter from this function shall return a handle of the printer, but when I used the labview node to call this function, the output variable returns zero, which means the function call is not working. I suspected the cause is probably due to that I did not correctly pass the second input parameter to the function. I will really appreciate if you could take time to try to run your code to see if you could get it to work.
This is not trivial.
The function prototype is
BOOL WINAPI OpenPrinterA(LPSTR lpPrinterName,HANDLE *phPrinter, LPPRINTER_DEFAULTSA pDefault);
The second parameter would be no problem you just treat it as a pointer to an uInt32 but the third is a pain. Its structure definition is:
typedef struct _PRINTER_DEFAULTSA {
LPSTR pDatatype;
LPDEVMODEA pDevMode;
ACCESS_MASK DesiredAccess;
} PRINTER_DEFAULTSA, *LPPRINTER_DEFAULTSA;
with all but the ACCESS_MASK parameter being a pointer to some memory. You could pass in a NULL for this parameter in which case certain defaults will be assumed and you could theoretically change them later on by calling SetJob().
But here comes the crux of this: Using the returned printer handle for anything (with or without having specified a valid defaults structure) will require you to call many more Windows API functions, and some of them are even more complex than this one. All in all if you really need to do something by opening the Printer Driver in winspool.drv, it is a much better idea to implement that in an external DLL written in C with a LabVIEW friendly calling interface and import that into your LabVIEW application instead.
Rolf Kalbermatter
Rolf Kalbermatter
CIT Engineering Netherlands
a division of Test & Measurement Solutions

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How to Use LABVIEW charts with Mathscript

Hi,
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Well Chris,
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Waleed El-Badry MSc.,MCPD, ISTQB Certified Tester
Assistant Lecturer
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Attachments:
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My application is fairly complex. It is a real world testing applications that simultaneously controls 16 servo motors running various stress testing routines asynchronously and all at the same time. The application includes queues, state machines, sub VI's, dynamically launched VI's, subpanels, semaphores, XML files, ini files, global variables, shared variables, physical analog and digital interfaces and industrial networking. Just about every technique and trick that LabView 2010 has to offer and the kitchen sink as well.
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I'm not an expert but I'm charged out as one at work.
I am off today so I'll share some thoughts that may help or possibly inspire others to chime. I have tried to continually improve my code in those areas and would greatly welcome others sharing their approaches and insights.
Note:
I do refactoring services to help customers with this situation. What I will write does not represent what we do in a code review since our final delverable is a complete final design and that is beyond the scope of this reply.
I'll comment on your points.
dbaechtel wrote:
My application is fairly complex. ...
While watching Olympic figure skating competion slow-motion replays, I learned how the subtleties of how the launching skate is planted while entering a jump can make the difference between a good jump and a bad one.
In software, we plant our foot when we turn from the design to the development. I have to admit that there where a couple of times when I moved from design to development too early and found myself in a situation like you have described.
How to know when design is done?
Waterfall says "cross every 't' and dot every 'i' " while Agile says "code now worry about design latter" and Bottom-up "says "demo working why bother designing" (Please feel free to coment on these over-simplifications gang).
My answer is not much more helpful for those new to LabVIEW.
My design work is done when my design diagrams are more complicated than the LabVIEW diagrm they describe.
dbaechtel wrote:
simultaneously controls 16 servo motors running various stress testing routines asynchronously and all at the same time. The application includes ...and the kitchen sink as well.
Have you posted any design documents you have? These will help greatly in letting us understand your application. More on diagrams latter.
Anytime I see multiple "variations on a theme", I think LVOOP (LabVIEW OOP ) . I'll spare you the LVOOP sales pitch but will testify that once you get your first class cloned off and running as a sibling (or child) you'll appreciate how nice it is to be able to use LVOOP.
Discalimer:
If you don't already have an OOP frame of mind, the learning curve will be steep.
dbaechtel wrote:
Still I am not happy with the productivity that LabVIEW 2010 has provided, nor the readability of my final product.
Sometimes there are too many wires....going from input to output, doing nothing,... spend alot of time bundling and unbundling and rebundling those values, but I don't think that would improve things much.
Full disclaimer:
I used to be of the same opinion and even used performance arguements to make my point. I have since, changed my mind.
Let me illustrate (hopefully). This link (if it works for you, use lefthand pane to navigate hierachy) shows an app I wrote from about 10 years ago when I was in my early days of routing wires. Even the "Main" VI started to suffer from too many wires as this preview from that links shows.
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When I wrote "related data" I am refering data normalization rules (which my wife knows and I picked-up from her and I claim no expertise in this area) where only values that are used together are grouped. E.G. Cluster named File contains "Path" and "Refnum" but not "PhaseOfMoon". This works out nicely with first creating sub-VI since all of the data related to file operations are right there whe I need it and it leads into the next concept ...
When I look at a value in a shift register on the diagram taking up space that is only used in a small sub-set of states, I concider using an Action Engine . This moves the wire from the current diagram into the Action Engine (AE), and cleans up the diagram. The AE brings with it built-in protection so provided I keep all of the opearations related to the the Type def inside the AE I am protected when I start using multiple threads that need at that data (trust me, it may not make a difference now but end users are clever). So that extra wire is effective encapsualted and abstracted away from the diagram you are looking at.
But I said earlier that I would not sell LVOOP so I'll show you what LVOOP based LV apps look like to contrast what I was doing ten years ago in that earlier link. This is what the top level VI looks like.
And this is the Analysis mode of that app.
I suspose I should not mention that LVOOP has wizards that automatically create the sub-VI (accessors) that bundle/unbundle the clusters, should I?
Continuing...
dbaechtel wrote:
We have had a long discussion about the use or misuse of Local variables...I also have a bug whenever I try and copy some code...
If you can simplify the code and duplicat ethe bug. please do so. We can get it logged and fixed.
dbaechtel wrote:
I am also having trouble using trouble using Variable Property Nodes....
That sounds like a usage issue. Posting code to illustrate the process will et us take a shot at figuring out what is happening.
dbaechtel wrote:
Creating subVIs is often not appropriate... My application already has over 150 sub VIs.
"Back in the day..." LV would not even try to create a sub-VI that involved controls/indicators. I use sub-VIs to maintain a common GUI often but I do it on purpose and when I find myself creating a sub-VI that involves a control/indicator, I hit ctrl-z immediately!
I figure a way around it (AE ?) and then do the sub-VI.
Judging by your brief explanation and assuming you do a LVOOP implementation, I would estimate that app need 750-1500 VIs.
dbaechtel wrote:
The LabView Clean Up Diagram function often works poorly....
THe clean-up works fine for how I use it. After throwing together "scratch code" and debugging the "rats nest" I'll hit clean-up as a first step. It guess good enough on simple digrams and in some cases inspires me to structure the diagram in a different way that I may not have thought about. If I don't like, ctrl-z.
Good deisgn and modualr implementaion led to smaller diagrams that just don't need thrre screens.
dbaechtel wrote:
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Smaller diagrams single step faster since the sub-VI run full speed. I cringe thinking about a 3-screen diagram with multiple probes open ( shivver!).
Re: Nestested structres
Sub-VIs (wink, wink, nudge, nudge)
If it works you have prven the concept is possible. That is the first step in an application.
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