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In this lesson, you will learn how to use the low-level File I/O VI and functions.

Use the following low-level File I/O VI and functions to perform basic file I/O operations:

  • Open/create/replace file

    Opens an existing file, creates a new file, or replaces an existing file, programmatically or interactively using afile dialog box. You can optionally specify a dialog prompt, default file name, start path, or filter pattern. If filepath is empty, the VI displays a dialog box from which you can select a file.
  • Read file

    Reads data from an open file specified by refnum and returns it in data. Reading begins at the current file mark or alocation specified by pos mode and pos offset. How the data is read depends on the format of the specified file.
  • Write file

    Writes data to an open file specified by refnum. Writing begins at a location specified by pos mode and pos offsetfor byte stream files and at the end of the file for datalog files. data, header, and the format of the specified filedetermine the amount of data written.
  • Close file

    Closes an open file specified by refnum and returns the path to the file associated with the refnum. Error I/O operatesuniquely in this function, which closes regardless of whether an error occurred in a preceding operation. Thisensures that files are closed correctly.

Error handling

The low-level File I/O VIs and functions return error information. Wire the error information from the beginning ofthe VI to the end. Include an error handler VI, such as the Simple Error Handler VI located on the Time&Dialog palette, at the end of the VI to determine if the VI ran without errors. Use the error inand error out clusters in each VI you use or build to pass the error information through the VI.

Saving data in a new or existing file

You can write any data type to a file you open or create with the File I/O VIs and functions. If other users or applicationsneed to access the file, write string data in ASCII format to the file. Refer to the LabVIEW Basics II: Development Course Manual for more information about writing LabVIEW datalog or binary files.

You can access files either programmatically or interactively through a file dialog box. To access a file through a dialogbox, do not wire file path in the Open/Create/Replace File VI. However, you can save time by programmatically wiring the default filename andpath to the VI. describes how pathnames are organized.

Platform Pathname
Windows Consists of the drive name, a colon, backslash-separated directory names, and thefilename. For example, c:\testdata\test1.dat is the pathname to a file named test1.dat in the testdata directory.
UNIX UNIX Consists of forward slash-separated directory names and the filename. For example, /home/testdata/test1.dat is the pathname to a file named test1.dat in the testdata directory in the /home directory. Filenames and pathnames are case sensitive.
Mac OS Consists of the volume name (the name of the disk), a colon, colon-separated folder names, and thefilename. For example, Hard Disk:testdata:test1.dat is the pathname to a file named test1.dat in a folder named testdata on a disk named Hard Disk .

The block diagram shown in shows how to write string data to a file while programmatically wiring thefilename and pathname. If the file already exists, it is replaced; otherwise a new file is created.

The Open/Create/Replace File VI opens the file test1.dat . The VI also generates a refnum and an error cluster.

When you open a file, device, or network connection, LabVIEW creates a refnum associated with that file, device, or network connection. All operations you perform onopen files, devices, or network connections use refnum s to identify each object.

The error cluster and refnum pass in sequence from one node to the next. Because a node cannotexecute until it receives all its inputs, passing these two parameters forces the nodes to run in order and creates a datadependency. The Open/Create/Replace File VI passes the refnum and error cluster to the Write File function, which writes the data to disk. When the Write File function finishes execution, it passes the refnum and error cluster to the Close File function, which closes the file. The Simple Error Handler VI examines the error cluster and displays a dialog box if an error occurred.If an error occurs in one node, subsequent nodes do not execute, and the VI passes theerror cluster to the Simple Error Handler VI.

Questions & Answers

can someone help me with some logarithmic and exponential equations.
Jeffrey Reply
sure. what is your question?
ninjadapaul
20/(×-6^2)
Salomon
okay, so you have 6 raised to the power of 2. what is that part of your answer
ninjadapaul
I don't understand what the A with approx sign and the boxed x mean
ninjadapaul
it think it's written 20/(X-6)^2 so it's 20 divided by X-6 squared
Salomon
I'm not sure why it wrote it the other way
Salomon
I got X =-6
Salomon
ok. so take the square root of both sides, now you have plus or minus the square root of 20= x-6
ninjadapaul
oops. ignore that.
ninjadapaul
so you not have an equal sign anywhere in the original equation?
ninjadapaul
Commplementary angles
Idrissa Reply
hello
Sherica
im all ears I need to learn
Sherica
right! what he said ⤴⤴⤴
Tamia
what is a good calculator for all algebra; would a Casio fx 260 work with all algebra equations? please name the cheapest, thanks.
Kevin Reply
a perfect square v²+2v+_
Dearan Reply
kkk nice
Abdirahman Reply
algebra 2 Inequalities:If equation 2 = 0 it is an open set?
Kim Reply
or infinite solutions?
Kim
The answer is neither. The function, 2 = 0 cannot exist. Hence, the function is undefined.
Al
y=10×
Embra Reply
if |A| not equal to 0 and order of A is n prove that adj (adj A = |A|
Nancy Reply
rolling four fair dice and getting an even number an all four dice
ramon Reply
Kristine 2*2*2=8
Bridget Reply
Differences Between Laspeyres and Paasche Indices
Emedobi Reply
No. 7x -4y is simplified from 4x + (3y + 3x) -7y
Mary Reply
is it 3×y ?
Joan Reply
J, combine like terms 7x-4y
Bridget Reply
im not good at math so would this help me
Rachael Reply
yes
Asali
I'm not good at math so would you help me
Samantha
what is the problem that i will help you to self with?
Asali
how do you translate this in Algebraic Expressions
linda Reply
Need to simplify the expresin. 3/7 (x+y)-1/7 (x-1)=
Crystal Reply
. After 3 months on a diet, Lisa had lost 12% of her original weight. She lost 21 pounds. What was Lisa's original weight?
Chris Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
China
Cied
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
Porter
many many of nanotubes
Porter
what is the k.e before it land
Yasmin
what is the function of carbon nanotubes?
Cesar
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
AMJAD
preparation of nanomaterial
Victor Reply
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
Himanshu Reply
good afternoon madam
AMJAD
what is system testing
AMJAD
what is the application of nanotechnology?
Stotaw
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
Azam
anybody can imagine what will be happen after 100 years from now in nano tech world
Prasenjit
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
Azam
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
Prasenjit
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
Damian
silver nanoparticles could handle the job?
Damian
not now but maybe in future only AgNP maybe any other nanomaterials
Azam
can nanotechnology change the direction of the face of the world
Prasenjit Reply
At high concentrations (>0.01 M), the relation between absorptivity coefficient and absorbance is no longer linear. This is due to the electrostatic interactions between the quantum dots in close proximity. If the concentration of the solution is high, another effect that is seen is the scattering of light from the large number of quantum dots. This assumption only works at low concentrations of the analyte. Presence of stray light.
Ali Reply
the Beer law works very well for dilute solutions but fails for very high concentrations. why?
bamidele Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, Pdf generation test course - alternate pdf style. OpenStax CNX. Jul 11, 2012 Download for free at http://legacy.cnx.org/content/col11436/1.3
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