BACS 287

BACS 287

Visual Basic String Manipulation

BACS 287

Visual Basic Strings

In Visual Basic, a “string” is a series of text, numbers, and special characters.

Strings are stored in string variables. String values are always enclosed in

quotation marks. There is only 1 built-in operator that works on

strings (the ‘&’ operator).

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String Characteristics

All strings in Visual Basic are variable-length strings.

A variable-length string can contain up to approximately 2 billion characters.

Generally speaking, string variables can contain any character represented on the keyboard.

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String Examples

The following are examples of defining and manipulating strings.Dim strInput as string = “ABC 123”

Dim strOutput as string = “def ,/ 56r”

Dim strX as string

strX = strInput & strOutput

Results in strX value of “ABC 123def ,/ 56r”

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Operations on Strings

There are 2 basic ways to manipulate strings in Visual Basic– Using built-in string functions– Using string methods

Methods associated with string variables are the more modern way to manipulate strings

You can use either methods or functions; both achieve the same results; however, methods are the preferred way.

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String Methods

There are several methods automatically associated with all string variables.

Determine current string state:string.Length – returns the number of characters in a stringstring.Compare – determine if two strings are the samestring.IsNullOrEmpty – determine if a string is null or emptystring.StartsWIth – determine if a group of characters is at start of a stringstring.EndsWith – determine if a group of characters is at end of a stringstring.Contains – determine if a string contains a group of characters (Boolean)string.IndexOf – find the starting location of a substring within the string

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String Methods

Modify edges of string:

string.TrimStart – removes leading characters from a string

string.TrimEnd – removes trailing characters from a string

string.Trim – removes leading and trailing characters from a string

string.PadLeft – adds characters to the beginning of a string

string.PadRight – adds characters to the end of a string

Convert string to different format:

string.ToUpper – convert all characters to upper case

string.ToLower – convert all characters to lower case

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String Methods

Add / Remove characters in existing string:

string.Remove – removes characters from anywhere in a string

string.Substring – extract a substring from the string

string.Replace – replaces characters with other characters in a string

string.Insert – adds characters within a string

Manipulate string into different string / array:

string.CopyTo – copies a specified number of characters to an array

string.Split – returns a string array of delimited elements from the original string

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String Functions

Most of the same string manipulations can be performed with system defined functions.

INSTR - returns the position of the first occurrence of one string within another

MID - Returns the specified number of characters from a string

LEN - Returns the number of characters in a string

LEFT / RIGHT - Returns the specified number of characters from the left/right side of a string.

UCASE / LCASE - Returns a string that has been converted to uppercase or lowercase

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String Functions

TRIM / RTRIM / LTRIM - Returns a copy of a string without leading spaces (Ltrim), trailing spaces (Rtrim), or both leading and trailing spaces (Trim).

FORMAT - Formats an expression according to instructions contained in a format expression.

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InStr Function

The InStr function is used when you want to find the first occurrence of one string within another.

It returns the position of where the match is found, 0 if it is not found.

Syntax:

InStr (start, string1,string2,[compare])

NOTE: You start counting at 1 with this command

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InStr Function Example

SearchString ="XXpXXpXXPX XP“ ' String to search in (note that position 11 is a space).

SearchChar = "P" ' Search for "P".IntStartPos = 7 ‘ Start in position 7

' A textual comparison starting at position 4. Returns 6MyPos = InStr(4, SearchString, SearchChar, 1)

' Comparison is binary by default (last argument is omitted).MyPos = InStr(SearchString, SearchChar) ' Returns 9

MyPos = InStr(1, SearchString, " ") ' Returns 11 (started in pos 1)MyPos = InStr(intStartPos, SearchString, "p") ' Returns 0 (did not find it)

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Mid Function

The MID function is used to extract characters from a string.

It is commonly used with InStr to pull out the sub-string that was located.

Syntax:

Mid (string, start, [length])

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Mid Function Example

MyString = "Mid Function Demo" ' Assign text string.

FirstWord = Mid(MyString, 1, 3) ' Returns "Mid".

LastWord = Mid(MyString, 14, 4) ' Returns "Demo".

MidWords = Mid(MyString, 5) ' Returns "Function

' Demo".

strOut = Mid(MyString, InStr(1,MyString,”F”), 8) ' Returns “Function”

InStr function returns 5

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Determine String Length

The Length method and the Len function may be used to determine the number of characters in a string.

The Len function can also be used to determine the number of bytes to store a variable (somewhat obscure).

Syntax: string.length

Len (string | variable)

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Determine String Length Example

Dim MyString as string = “Hello World”Dim MyInt As IntegerDim MyCur As Currency

‘ use methodMyLen = MyString.Length ‘ returns 11

‘ use functionMyLen = Len(MyString) ' Returns 11.MyLen = Len(MyInt) ' Returns 2.MyLen = Len(MyCur) ' Returns 8.

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Modify String Edges Operations

The Left and Right functions are used to extract characters from the left and right side of a string.

The original string is not modified

Syntax:

Left (string,length)

Right (string,length)

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Left / Right Example

AnyString = "Hello World" ' Define string.

MyStr = Left(AnyString, 1) ' Returns "H".

MyStr = Left(AnyString, 7) ' Returns "Hello W".

MyStr = Left(AnyString, 20) ' Returns "Hello World".

MyStr = Right(AnyString, 1) ' Returns "d".

MyStr = Right(AnyString, 6) ' Returns " World".

MyStr = Right(AnyString, 20) ' Returns "Hello World".

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Ucase / Lcase Function

The Ucase and Lcase functions return a string with the case changed to upper or lower.

Syntax:

Ucase (string)

Lcase (string)

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Ucase / Lcase Example

strInput = "Hello World 1234" ' String to convert.

UpperCase = UCase(strInput) ' Returns "HELLO WORLD 1234".

LowerCase = LCase(strInput) ' Returns ”hello world 1234".

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Ltrim / Rtrim / Trim Function

The Ltrim, Rtrim, and Trim functions remove leading spaces, trailing spaces, and both leading and trailing spaces.

Syntax:

LTrim (string)

RTrim (string)

Trim (string)

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LTrim / Rtrim / Trim Function

MyString = " <-Trim-> " ' Initialize string

TrimString = LTrim(MyString) ' TrimString = "<-Trim-> ".

TrimString = RTrim(MyString) ' TrimString = " <-Trim->".

TrimString = LTrim(RTrim(MyString)) ' TrimString = "<-Trim->".

' Using the Trim function alone achieves the same result as the previous example.

TrimString = Trim(MyString) ' TrimString = "<-Trim->".

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Format Function

The Format function is used format a string expression based upon instructions given in a “format expression”.

The rules for this function are very complex and are best learned via the VB help screens.

Syntax:

Format(expression,[format,[firstdayof week,[firstweekofyear]]])

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Format Function Examples

MyTime = #17:04:23#

MyDate = #January 27, 1999#

' Returns current system time in the system-defined long time format.

MyStr = Format(Time, "Long Time")

' Returns current system date in the system-defined long date format.

MyStr = Format(Date, "Long Date")

MyStr = Format(MyTime, "h:m:s") ' Returns "17:4:23".

MyStr = Format(MyTime, "hh:mm:ss AMPM") ' Returns "05:04:23 PM".

MyStr = Format(MyDate, "dddd, mmm d yyyy") ' Returns "Wednesday,

' Jan 27 1993".

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Format Function Examples

' If format is not supplied, a string is returned.

MyStr = Format(23) ' Returns "23".

' User-defined formats.

MyStr = Format(5459.4, "##,##0.00") ' Returns "5,459.40".

MyStr = Format(334.9, "###0.00") ' Returns "334.90".

MyStr = Format(5, "0.00%") ' Returns "500.00%".

MyStr = Format("HELLO", "<") ' Returns "hello".

MyStr = Format("This is it", ">") ' Returns "THIS IS IT".

See Visual Basic help screens for more format expression details.

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Nesting String Functions

You can nest string functions inside each other. The innermost function is performed first and the outermost is performed last.

Example:Dim MyString as string = ” nested function demo “

strX = Mid(Ucase(Trim(MyString)), InStr(1,Ucase(Trim(MyString)),”UNC”), 8)

' Returns “UNCTION ”

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Nesting String Functions

This also works with string methods.

Example:Dim MyString as string =” nested function demo “

strX = MyString.Substring((MyString.Trim.ToUpper.IndexOf("UNC", 0) + 2), 8).ToUpper

' Returns “UNCTION ”