Virtual Instrumentation-Concept of
Strings and File I/O
Dr. Jainy Sachdeva
Associate Professor
EIED, TIET, PATIALA
Course: VIRTUAL INSTRUMENTATION (UEI-844)
Faculty Name: Dr. Jainy Sachdeva (Associate Professor)
(Course Coordinator)
Lecture Contents:
Concept of Strings & File I/O
 Introduction to Strings
 Functions of Strings
 Functions of File I/O
Contents of this lecture are based on the following books:
1. Johnson, G., LabVIEW Graphical Programming, McGraw Hill (2006).
2. Sokoloft, L., Basic Concepts of LabVIEW 4, Prentice Hall Inc. (2004).
3. Wells, L.K. and Travis, J., LabVIEW for Everyone, Prentice Hall Inc. (1996).
2
Introduction
A string is a sequence of displayable or non-displayable ASCII characters.
Strings provide a platform-independent format for information and data.
Strings often are used to send commands to instruments, to supply information
about a test (such as operator name and date), or to display results to the user.
Applications
 Creating simple text messages.
 Controlling instruments by sending text commands to the instrument and
returning data values in the form of either ASCII or binary strings which you
then convert to numeric values.
 Storing numeric data to disk.
 To store numeric data in an ASCII file, you must first convert numeric data to
strings before writing the data to a disk file.
 Instructing or prompting the user with dialog boxes.
String Controls / Indicators
String Controls are used to input a text.
String Indicators are used to display a text.
The string control and indicator is located on the Controls»Text Controls and
Controls»Text Indicators palettes to simulate text entry boxes and labels.
 Right-click a string control or indicator on the frontpanel to select from the display
types.
Fig:- Message for each Display
Examples - Display Types
Fig:-Normal Display
Fig:-Code Display
Fig:-Password Display
Fig:-Hex Display
String Functions
String functions behave similarly to array functions; in fact,
strings are really just arrays of ASCII data.
Use the String functions to concatenate two or more strings,
extract a subset of strings from a string, convert data into
strings, and format a string for use in a word processing or
spreadsheet application.
Fig:-All String Functions in Law View
String Length
 Returns in length the number of characters (bytes) string, including spaces &
characters.
 For example, the String Length function returns a length of 19 for the following
string:The quick brown fox.
Fig:-String Length
Concatenate Strings
 Concatenates input strings and 1D arrays of strings into a single output string.
 For array inputs, this function concatenates each element of the array.
 Add inputs to the function by right-clicking an input and selecting Add Input
from the shortcut menu or by resizing the function.
Fig:-Concatenate Strings
String Subset
 Returns the substring of the input string beginning at offset and containing length
number of characters.
 The offset of the first character in string is 0. For example, if you use the string
Volts DC+1.22683E+1; as the input, the String Subset function returns the
following substring for an offset of 6 and a length of 2: DC.
Fig:-String Subset
Match Pattern
 Searches for regular expression in string beginning at offset, and if it finds a match, splits string into
three substrings.
 If no match is found, match substring is empty and offset past match is –1. For example, use a regular
expression of + and use the following string as the input: VOLTS DC+1.22863E+1.
 The Match Pattern function returns a before substring of VOLTS DC, a match substring of +, an after
substring of 1.22863E+1, and an offset past match of 9.
 A regular expression requires a specific combination of characters for pattern matching.
Fig:-Match Pattern
Match Regular Expression
Searches for a regular expression in the input string beginning at the offset you enter.
 If the function finds a match, it splits the string into three substrings and any number of
submatches.
 Resize the function to view any submatches found in the string.
Array to Spreadsheet String
Fig:-Match Regular Expression
Converts an array of any dimension to a table in string form.
They containing tabs separating column elements, a platform-dependent EOL character separating
rows, for arrays of three or more dimensions, headers separating pages.
Fig:-Array to Spreadsheet String
Build Text
Creates an output string from a combination of text and parameterized inputs.
If the input is not a string, this Express VI converts the input into a string based on the
configuration of the Express VI
Carriage Return Constant
Consists of a constant string containing the ASCII CR value.
Empty String Constantnverts
Consists of a constant string that is empty (length zero).
Fig:-Build Text
End of Line Constant
Consists of a constant string containing the platform-dependent end-of-line value.
Format Date/Time String
 Displays a timestamp value or a numeric value as time in the format you specify using
time format codes.
 Time format codes include the following:
 %a (abbreviated weekday name)
 %b (abbreviated month name)
 %c (locale-specific date/time)
 %d (day of month)
 %H (hour, 24-hour clock)
Fig:-Format Date and Time String
 %I (hour, 12-hour clock)
.
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

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


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
%m (month number)
%M (minute)
%p (a.m./p.m. flag)
%S (second)
%x (locale-specific date)
%X (locale-specific time)
Fig:-Format Date and Time String
%y (year within century)
%Y (year including century)
%<digit>u (fractional seconds with <digit> precision).
Format Into String
.
Formats string, path, enumerated type, time stamp, Boolean, or numeric data as text.
Line Feed Constant
Consists of a constant string containing the ASCII LF value.
Replace Sub String
Inserts, deletes, or replaces a substring at the offset you specify in
string.
Fig:-Replaced Sub String
Thank you…
Virtual Instrumentation-Concept of
Strings and File I/O
Dr. Jainy Sachdeva
Associate Professor
EIED, TIET, PATIALA
Course: VIRTUAL INSTRUMENTATION (UEI-844)
Faculty Name: Dr. Jainy Sachdeva (Associate Professor)
(Course Coordinator)
Lecture Contents:
Concept of Strings & File I/O
 Introduction to Strings
 Functions of Strings
 Functions of File I/O
Contents of this lecture are based on the following books:
1. Johnson, G., LabVIEW Graphical Programming, McGraw Hill (2006).
2. Sokoloft, L., Basic Concepts of LabVIEW 4, Prentice Hall Inc. (2004).
3. Wells, L.K. and Travis, J., LabVIEW for Everyone, Prentice Hall Inc. (1996).
20
Spreadsheet String to Array
Array—Converts the spreadsheet string to an array of the dimension and representation
of array type.
This function works for arrays of strings and arrays of numbers.
Scan from String
Fig:-Spread Sheet String To Array
Scans the input string and converts the string
according to format string.
Use this constant to supply a one-character
space string to the block diagram.
Fig:-Scan From String
Search & Replace String
 Replaces one or all instances of a substring with another substring. To include the
multiline? input and enable advanced regular expression searches, right-click the
function and select Regular Expression.
Space Constant
Use this constant to supply a one-character
space string to the block diagram.
Fig:-Search and Relace
String Constant
Use this constant to supply a constant text string to the block diagram.
Tab Constant
Consists of a constant string containing the ASCII HT (horizontal tab) value.
To Lower Case
Fig:-To Lower Case
Converts all alphabetic characters in string to lowercase characters.
Evaluates all numbers in string as ASCII codes for characters. This function does not affect non-alphabetic
characters.
To Upper Case
Fig:-To Upper Case
Converts all alphabetic characters in string to uppercase characters.
Evaluates all numbers in string as ASCII codes for characters. This function does not affect non-alphabetic
characters.
Trim WhiteSpaces
Whitespace—Removes all white space (spaces, tabs,
carriage returns, and linefeeds) from the beginning, end, or
both ends of string.
Fig:-Trim White Spaces
Converting Numeric Values to Strings
Build Text Express VI




Use the Build Text Express VI to convert numeric values into strings.
The Build Text Express VI,located on the Functions»Output palette,
concatenates an input string.
If the input is not a string, this Express VI converts the input into a string based
on the configuration of the Express VI.
When you place the Build Text Express VI on the block diagram, the Configure
Build Text dialog box appears.
Converting Strings to Numeric Values
Scan from String
The Scan From String function converts a string containing valid numeric
characters, such as 0–9,+, –, e, E, and period (.), to a numeric value. This
function scans the input string and converts the
string according to format string.
 Use this function when you know the exact format of the input text.
 This function can scan input string into various data types, such as numeric
or Boolean, based on the format string. Resize the function to increase the
number of outputs.

Fig:-Scan from String
Converting Numeric Values to Strings
Example


An Express VI is configured to accept one input, voltage, and change it to a
fractional number with a precision of 4. The input concatenates the resultant
voltage to the string “Voltage is”.
The parameters are defined in Configure Build Text dialog box.
Fig:-Convert Numeric Values To String
Fig:-Convert Numeric Values To String
Format String
specifies how to
convert the input string
into the output
arguments
Scan from String
Remaining string returns
the portion of the string
that remains after scanning
all arguments.
Input String is the
string, path, enum
type, time stamp or
numeric data to scan
Offset past scan is the
offset of input string
after the scan (i.e
position)
Initial Scan location is
the offset into the
string where scan
begins. Default is 0
Error out contains
error information
incase it runs into one
Default 1..n specifies the type
and default value for the
output parameters. If this
function cannot scan the input
value from format string, the
function uses the default.
Output 1..n specifies the output
parameters. Each output can be a
string, path, enumerated type, time
stamp, Boolean, or any numeric
data type. You cannot use arrays
and clusters with this function.
Converting Strings to Numeric
Example
●
●
For example as shown in Figure 9.3 use a
format string of %f, an initial search location
of 8, and VOLTS DC+1.28E+2 as the input
string, to produce an output of 128.
Change the precision of the output by
changing the precision of the indicator. In
format string, % begins the format specifier
and f indicates a floating-point numeric with
fractional format.
Fig:- String To Numeric
Fig:- String To Numeric
Example- Concatenate Strings


This example takes two inputs, string & string 2 &
concatenates them using the Concatenate String
function discussed earlier.
The output is then shown in a String Indicator.
Fig:-Concatenate String
Fig:-Concatenate String
File Input and Output ( I/O)
Four Hierarchy Levels:
High-level File VIs
Intermediate File VIs andFunctions
Advanced File Functions sub-palette
Express VIs
High-level File I/O VIs
● Write to Spreadsheet File
● Read from Spreadsheet File
● Write Characters to File
● Read Characters from File
● Read Lines from File
Write to File Example
● Open/Create/Replace opens the existing file TEST1.DAT and generates refnum and
error cluster
● Write File writes the data
Close File closes the file
● Simple Error Handler checks for errors.
Reading Data from a File
●
●
●
●
Open/Create/Replace opens the file
Read File reads the specified number of bytes from the file
Close File closes the file
Simple Error Handler checks for errors
Formatting a Spreadsheet String
● Spreadsheets are popular tools
for data handling and
analysis
● There are many formats for
spreadsheet data. One of the
● most popular is tab-delimited:
● – Columns are separated by a
tab character
● – Rows are separated by an endof-line character
Example of Formatting a Spreadsheet String
Creating a Spread Sheet
Can replace Format Into String and
Write File with Format Into File in above example
Write LabVIEW Measurement File
Includes the open, write, close and error
● Handling functions
Handles formatting the string with either a tab or comma
delimiter
● Merge Signals function is used to combine data
into the dynamic data type
●
Example Lab VIEW Measurement File
Thank you…