Working with Strings
Counting the characters Removing spaces at the start and end Extracting characters from the left Extracting characters from the right hand-side Getting characters from the middle
Strings are a useful data-type in Visual Basic and they become even more useful when you start to use some of the functions that VB6 provides to work with them.
This tutorial will introduce you to the following functions:
| Function | Description |
| Len(string) | Returns the length of the string |
| Trim(string) | Removes any spaces at the start and end of the string |
| Mid$(string, start, count) | Returns a number of characters from the middle of a string |
| Left$(string, count) | Returns a number of characters on the left of a string |
| Right$(string, count) | Returns a number of characters on the right-hand side of a string |
Len
This function counts how many characters there are in the string. This can be really useful if you need to check if the user has entered too many characters in a textbox (if you haven't used the MaxLength property).
Another use is to check if a line of text that you've just read from a textfile is the expected length (you might do this to prevent the user manually editing the textfile).
Example
Private Sub Form_Load()
Dim strExample As String
Dim iStringLength As Integer
' Assign a sentence to strExample
strExample = "This is an example string"
' Find out how many characters are in strExample
' and store the value in iStringLength
iStringLength = Len(strExample)
' Tell the user how many characters are in the string
MsgBox "The string has " & Str(iStringLength) & " characters."
End Sub
Trim
Trim is a really useful function that gets rid of any whitespace at the start and end of a string. Whitespace includes spaces and tabs.
This is a really useful way of making sure that the user hasn't accidentally typed a space at the start (or end of a string).
Trim does not remove whitespace from the middle of strings.
Example Code
Private Sub Form_Load()
Dim strExample As String
Dim strTrimmed As String
' Assign a sentence to strExample
strExample = " This is an example string "
' Trim strExample and store the result in strTrimmed
strTrimmed = Trim(strExample)
' Show the string before and after trimming
MsgBox "Before : **" & strExample & "**" & Chr(10) & Chr(13) & _
"After : **" & strTrimmed & "**"
End Sub
Left$
Left$ returns a string that contains a number of characters from the left-hand side of the input string. All you have to do is tell VB6 how many characters you want.
Usage
Left$(string,number_of_characters)
E.g. Left$("Chocolate cakes are yummy",9) would return "Chocolate".
Example code
Private Sub Form_Load()
Dim strExample As String
Dim strLeft As String
' Assign a sentence to strExample
strExample = "Chocolate cakes are yummy"
' Put the 9 left-most characters of strExample into strLeft
strLeft = Left$(strExample, 9)
' Display the contents of strLeft
MsgBox strLeft
End Sub
Right$
Right$ returns a string that contains a number of characters from the right-hand side of the input string. All you have to do is tell VB6 how many characters you want.
Usage
Right$(string,number_of_characters)
E.g. Right$("Chocolate cakes are yummy",5) would return "yummy".
Example Code
Private Sub Form_Load()
Dim strExample As String
Dim strRight As String
' Assign a sentence to strExample
strExample = "Chocolate cakes are yummy"
' Put the 5 right-most characters of strExample into strRight
strRight = Right$(strExample, 5)
' Display the contents of strRight
MsgBox strRight
End Sub
Mid$
Mid$ extracts the characters from the middle of the input string. You must supply the starting point in the string and how many characters to extract.
Usage
Mid$(string,starting_point,number_of_characters)
E.g. Mid$("Chocolate cakes are yummy",11,5) would return "cakes".
Example Code
Private Sub Form_Load()
Dim strExample As String
Dim strMid As String
' Assign a sentence to strExample
strExample = "Chocolate cakes are yummy"
' Get 5 characters from strExample, starting at character 11
and store in strMid
strMid = Mid$(strExample, 11, 5)
' Display the contents of strMid
MsgBox strMid
End Sub