Q: How many software engineers does it take to change a light bulb ?
A: It can't be done; it's a hardware problem.
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LabWindows/CVI is a great package from National Instruments. Its main purpose is to be a powerful tool for writing data acquisition programs, but it's really a multipurpose 32 bits C compiler, doubled by a code generator and some of the most powerful C libraries ever seen on a PC (easy to use and very complete User Interface, signal/maths and more with Advanced Analysis, Data Acquisition, VXI, GPIB 488, VISA, TCP, DDE, formatting and I/O, Utilities and finally ANSI C). And that was when I originally wrote this page 20 years ago, nowadays there's a lot more.

Note: as of 2015, I offer an introductory/intermediate training course to LabWindows/CVI programming, of a duration of 3 or 4 days for up to 4 programmers with C experience. I can do this course in english, french or italian, and you can subscribe through Iris Training or contact me. The outline of the course is here.

There are a few things missing from early (or even current) versions of LabWindows. Here is some code I wrote or adapted for doing on the fly statistics, doing color scaling, getting compiled Html Help files (*.chm) to display contextual help and doing extended time formatting.

Since 2019, most of the code is available on my gitlab page.

If you are looking for my old ReadSavePng.fp and ReadSaveJpeg.fp, I removed them from the list thinking that they were obsolete due to the fact that you can now use the GetBitmapFromFile(), SaveBitmapToJPEGFile() and SaveBitmapToPNGFile() functions, yet there are a few additional functions in my libraries that are still useful; so just in case you can find the libraries in this gitlab project, just pull the appropriate files.

Showing all attributes

Sometimes there's something wrong with a control. It doesn't behave as expected. Maybe you changed an attribute with the wrong panel/control association. And the cause is hard to pinpoint since it can happen in a totally unrelated piece of code. Unless NI makes a SetBreakOnAttributeChange function, we are stuck with looking at the properties of the control. But we can't do that from the debugger, it needs to be done from the code itself. And to further complicate it, every type of control has different attributes.

So I wrote this little module to dump all the valid attributes off a panel or control. It just prints them all. Two source files: ShowAttributes.h and >ShowAttributes.c.

LabWindows/CVI user interface Panel, Debugging, Function
Original functions.
Published on gitlab (find the ShowAttributes source code there).

Have you ever noticed that in the user interface editor you can move between panels using Ctrl-shift and the left or right arrow ? Well, here's a little piece of code that allows you to do the same thing in your C programs. In addition it will print or center your panels on request. Note that on Linux the keymaps are a bit different so you may want to verify them.

In this small source code, you'll also find functions to handle default keys (print, screenshot...), replace fonts, auto-size controls, find all controls or panels that fit a given criterium, get the center of a control, place it near a certain point, make a panel or tab active, find if a panel if embedded in a tab, move panels between top-level and tabbed (SDI/MDI)...

LabWindows/CVI user interface Panel, Navigation, Tricks
Original functions.
Reshapped a bit.
Published on gitlab (find the PanelManagement source code there).

Edit axis settings popup

OK, so there are several predefined popups, like ConfirmPopup or GeneralPopup that you can call, and they will return the button clicked by the user. But how do I make a custom popup, for instance the classic [Yes|No|YesToAll|NoToAll|Cancel] popup ?

I mulled that one over for a while, until a suggestion from Martin J. Saxon: the trick is to call RunUserInterface again... Here's the sourcecode for the [Yes|No|YesToAll|NoToAll|Cancel] popup and others.

ANSI C, LabWindows/CVI Function Panel, Popup, Graphics
v1.0, original version.
Precision popup.
Published on gitlab (find the CustomPopups source code there).

Slider ramp settings popup

Here's another example which allows you to change the format, precision and padding of a numeric control.

Note: you may be thinking about doing the same for a graph properties popup, but this is largely done already if you use legends and enable [Interactive Legend].

And yet another example which allows you to change the format, precision and a few other attributes to a graph axis.

And yet another example which allows you to change some cosmetics on a slider popup, including the ramp colors, needle width, etc.

And yet another simpler example which allows you to change the ON and OFF colors of a simple LED or button.

More events

There are many default events in LabWindows, but some are missing. For instance you can drag and drop files from explorer onto a panel only if you call the EnableDragAndDrop function. Something else that is sometimes necessary is shift-click, ctrl-click and alt-click. The code is below. The thing I haven't been able to figure out yet is how to separate and get the coordinates of mouse-down and mouse-up on a canvas, which is necessary for drawing a box for instance.

ANSI C, Windows, LabWindows/CVI, User Interface
Original version.
#include <windows.h>
int CVICALLBACK cb_View (int panel, int control, int event, void *callbackData, int eventData1, int eventData2) {
	BOOL KeyShift, KeyCtrl, KeyAlt;
	// can be combined
	KeyShift=GetAsyncKeyState(VK_SHIFT)>>8;	// >>8 if the key is pressed right now,
	KeyCtrl =GetAsyncKeyState(VK_CONTROL)>>8;	// &0xFF if it's been pressed since the last call
	KeyAlt  =GetAsyncKeyState(VK_MENU)>>8;

	switch (event) {
			if (KeyShift) ...;
			if (KeyCtrl) ...;
			if (KeyAlt) ...;

Another trick that has to do with user input is to regroup the keyboard events to the top panel. For instance if you have a child or separate panel that catches a few keyboard event but you want all other keyboard events to go to the main one (useful for instance if the menu bar is only on the main panel), do the following in the child panel callback function:

switch (event) {
		switch (eventData1) {	// Keyboard events recognized by child panel
			case 'm': DoSomething(); return 1; // Act and swallow the event
		// Key not recognized, passed to Main window
		FakeKeystroke (eventData1);
		return 1;		// We swallow the event but fake it again

Non-deterministic time labels on strip chart.

Arbitrary time axis in strip charts

TRecent versions of CVI have added a SetCtrlAttribute (panel, control, ATTR_XFORMAT, VAL_ABSOLUTE_TIME_FORMAT) and also a relative time format. The problem is that the data must be sent to the strip chart precisely 1s apart. Thus you cannot use a timer which lacks the precision. So I wrote this set of functions which writes the dates as text labels on the axis. It should work with an arbitrary number of strip charts at the same time.

It works quite simply: you call TSL_Auto with the expected update rate of your data, and then you call TSL_PlotStripChart to add points to the strip chart. That's about all there is to it, even if the data comes at non-deterministic intervals. It can use any resolution from one second to a year.

Here are 3 examples at various time scales:

Library, LabWindows/CVI, User Interface, Graphics
Original version.
Fixed bug when using multiple strip charts
Finer-grained intervals
Tiny improvements
Published on gitlab (find the TimeStripLabel source code there).

Generic strip chart interface.

Generic strip charts

Strip charts are a good way to offer real-time display of data but their programming can be a tad tricky. Here's a piece of code that takes a bunch of variable pointers and gives the user the possibility to display what he wants on how many strip charts as he wants. Basically.

It works quite simply: load the GSC panel from GenericStripChartUI.uir, then call GSC_SetProperties, then call GSC_AddVariable as many times as needed. Done.

If you compile the project with the GSC_DEBUG option, you get a full example executable. Also you can compile the file with TimeStripLabel.c or PanelManagement.h for added functionality.

Library, LabWindows/CVI, User Interface
2012/02/21, first version.
2012/02/24, corrected fatal bug.
2012/02/29, added GenericXYplot (see below).
2012/03/05, added EditAxisSettingsPopup option.
2012/03/20, minor fixes.
2014/03/28, minor fixes.
2019/06/11, Published on gitlab (find the GenericStripChart source code there).

Generic XY plot interface.

Generic XY plots

X/Y plots are the main way to display one data versus another and here's a simple panel that will take an arbitrary list of double variables and lets the user chose a pair to display against each others. It will display data for a while and then silently remove the oldest to avoid overflow or overloaded display.

It works quite simply: load the GXY panel from GenericStripChartUI.uir (it's the same file as above, but does no require the use of strip charts), then call GXY_SetProperties, then call GXY_AddVariable as many times as needed. Done.


first version.
Added EditAxisSettingsPopup option.
Published on gitlab (find the GenericXYplot source code there).

LabWindows Real-Time

As of 2007, LabWindows can run as real-time. The setup is fairly complex: you develop your code on a Windows machine, in the usual CVI IDE, and then you push it onto a machine running a real-time minimalist OS called PharLap ETS. Now I've had some trouble getting that thing running. The remote machine (also called real-time target) can be a PC, a PXI box or some other compbination, but for PCs the requirements are actually pretty tight:

Now NI gives you several ways to configure the target. I'll speak first about the OS installation, then about the network config:

USB Boot
If you can boot from USB, go in Measurement & Automation Explorer (MAX), in [Tools][RT Disk Utilities] and create a Desktop PC utility USB drive. You can do several different things when booting from this drive: run the real-time OS, install it on the drive, test to see if the hardware is compatible with the RTOS... Below I'll detail the phases of a floppy install, but it applies to a USB install as well.
Floppy test
In MAX, create a Desktop PC Boot disk. Boot your remote system with it. It should finish with a message similar to "Initializing network... Device 1 - MAC address:... - (primary) System state: unconfigured". If you get an immediate lockup, the processor is probably not compatible. If you get an ETS Loader.ERR, make sure that you floppy drive is working properly (they are often full of dust or the floppies are so old as to be useless). You get another kind of message if your network card is not compatible.
Hard drive preparation
You need an empty disk, formated in FAT32, without MBR. Easier said than done. For instance departitionning an existing disk with [Start][Settings][Control Panel][Administrative Tools][Computer Management][Disk Management] won't work if you have grub or somesuch as a boot loader. Here's a clean way to do it:
Network configuration
NI documentation seems to imply that the network configuration happens by magic: the remote boots with the (non-possible) IP address, is seen from the master PC, and you configure and run it from there. Not quite. We have a tightly secured network and there was no way I could see an IP of There's no information in the NI documentation as to what kind of broadcast was happening, so we could try to allow it at the firewall level or somesuch.
CVI specific config
Go back to MAX, [Remote Systems], expand your target, [Software][Add/Remove software] (the button is above), select [LabWindows/CVI Runtime Engine for RT] and [LabWindows/CVI Network Variable], as well as other requirements (VISA...)

Anyway, to make a long story short, I wasn't able to properly run the RTOS on my test laptop: incompatible network card. It's the proper chipset but it needs to be PCI and not MiniPCI. End of the story for now.

LabWindows on Linux

As of version 8.0 (2007), National Instruments provides a version of LabWindows/CVI for Linux. It was updated in 2010. Here are some notes about using it.

Chose an RPM-based distro: Red Hat, Suse and a few others are in. Gentoo, Ubuntu are out unless you want to play with rpm/deb converters. NI lists a limited set of Linux distribution, but I've used another one with success, still RPM-based (Scientific Linux).
Non RPM ?
If you'd rather use a modern Linux such as Ubuntu, you can try to copy the rpms to a writable directory, then convert them to .deb using: alien --to-deb --scripts *.rpm
The original Linux CD I had contained a Linux runtime engine but no Linux compiler (cvicc). I have no idea what I can do with a runtime without compiler. Note that unlike the free distribution of the runtime on Windows, the distribution of the Linux runtime costs money. I have no idea why there's a difference but it's worth asking NI.
You need OpenMotif 2.2 for the user interface (quite archaic IMHO): sudo yum install openmotif22.
In my case I want CVI to run Visa USB drivers. Visa is on the install CD, but can also be downloaded from here.
Visa and a few other libraries are in the form of kernel modules, so if you change kernel version, you need to reinstall some of the CVI components. Note that I wasted time on the kernel issue for nothing: on Red Hat, the kernel gets installed in specific ways, either with # up2date kernel-devel or # up2date redhat-rpm-config rpm-build [...]. I used the manual way where you download the tar file from, put it in /usr/src, ln, make menuconfig, etc... This does not work with the NI kernel modules. The kernel must be installed in the approved Red Hat way.
The main difference with CVI for Windows is that there's no development environment... So you have to develop on Windows, particularly you have no choice for the UIR. I use a shared SMB folder between a Windows and a linux machine, create the project and the UIR files in the CVI IDE, compile and test on Windows. Then all I have to do is open a shell in the same directory on the Linux side and type cvicc project.prj to compile it. It creates an executable with the same name, but for Linux. Very simple.
Note that the compiler sometimes confuses Windows and Linux intermediate files, so if your compilation isn't huge, it's better to do rm -rf cvibuild* between each compile.
The underlying compiler is actually gcc and you can change the default parameters in the file /usr/local/natinst/cvi2010/bin/compile.ecc, for instance here I do change -g to -ggdb and -c99 to -gnu99 (to get rid of the 'warning : implicit declaration of function ...' message when using POSIX functions):
COMPFLAGS = -c -x c -m32 -fstack-protector-all
C89_FLAGS = -std=gnu89
C99_FLAGS = -std=c11
LINKFLAGS = -rdynamic -m32 -flto -fwhole-program
USE_LIBRY = nianlys;pthread;cvintwrk;ninetv
Debug Opt = -Og -ggdb
Release Opt = -O3
Warnings =
You can also change COMPLPATH to clang to use the same compiler than on Windows (just install clang).
The compilation step runs fine in a text shell, but in order to run the program on Linux from windows, you need X-Windows. The one integrated with cygwin keeps crashing, and I'm having more luck with Xming. But currently I simply develop on a virtualbox WinXP in a directory exported by VirtualBox, and compile on linux. There's a bug when working this way: if you remove some text from a text file, the CVI editor truncates it, but the junk content behind the truncation remains in the file, so the Windows compilation works fine while the Linux one gives errors on extraneous characters which you can't see in the CVI editor. If you close and reopen CVI or if you open the file with a Linux editor, you can see the problem. It's a pain.
Some additional NI libraries are installed with the compiler, they are present in /usr/local/vxipnp/linux/bin/) and can be linked to with 'cvicc -lvisa project.prj'.
Standard Linux libs can be used as well, for instance 'cvicc -lusb project.prj' for libusb which I've used with success to develop a USB driver for a custom instrument for both Linux and Windows.
Use cvicc -debug project.prj and then run it as kdbg ./project or kdbg ./project_dbg (depending on your target setting). Then do [File][Open source], type *.c and [OK] so that the debugger has all your source files ready for stepping into. Very usable if a little 'ancient' compared to the CVI debugger.
The linux version is a bit behind the Windows version. For instance I've had trouble compiling some functions from toolbox.h, such as GetDiskSize in version 8.0.
Predefined Macros
The only new macro that I can find is _NI_linux_. Of course, all the WIN something macros go away. Careful that the _CVI_ macro which normally gives the version number IS NOT DEFINED.
Here are some bugs I've noticed under Linux:

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Some tricks:

Other resources about LabWindows/CVI include: