Export (0) Print
Expand All

Strings

The String data type represents a series of characters (each representing in turn an instance of the Char data type). An instance of a string can be assigned to a literal value that represents a series of characters. For example:

Dim MyString As String
MyString = "This is an example of the String data type"

A String variable can also accept any expression that evaluates to a string. Examples are shown below:

Dim OneString As String
Dim TwoString As String
OneString = "one, two, three, four, five"
TwoString = OneString.Substring(5,3)  ' Evaluates to "two".
OneString = "1"
TwoString = OneString & "1"  ' Evalates to "11".

Any literal that is assigned to a String variable must be enclosed by quotation marks (""). Naturally, this makes creating a literal that contains quotation marks somewhat problematic. For example, the following code returns a compiler error:

Dim myString As String
myString = "He said, "Look at this example!""  ' This causes an error.

This code returns a compiler error because the compiler terminates the string after the second quotation mark, leaving the rest of the string hanging. To have a quotation mark represented in a string literal, you must represent it as two quotation marks. The following example demonstrates the correct way to include a quotation mark in a string:

Dim myString As String
' The value of myString is: He said, "Look at this example!"
myString = "He said, ""Look at this example!"""

In the above example, the two quotation marks preceding the word 'Look' exist in the string as a single quotation mark. The three quotation marks at the end of the line represent a quotation mark in the string and the string termination character.

A string can be thought of as a series of Char instances, and the String type has built-in functions that allow you perform many manipulations on a string that resemble the manipulations allowed by arrays. You may refer to a specific character in a string through the Chars property, which provides a way to access a character by the position in which it appears in the string. For example:

Dim myString As String = "ABCDE"
Dim myChar As Char
myChar = myString.Chars(3)  ' The value of myChar is "C".

In the above example, the Chars property of the string returns the third character in the string, which is "C," and assigns it to myChar. You can also get the length of a particular string through the Length property. If greater array-type manipulation of the string is necessary, you can convert it to an array of Char instances using the ToCharArray function of the string. For example:

Dim myString As String = "abcdefghijklmnop"
Dim myArray As Char() = myString.ToCharArray

The variable myArray now contains an array of Char instances, each representing a character from myString.

The Immutability of Strings

A string is immutable, which means its value cannot be changed once it has been created. How, then, does the following example make any sense?

Dim myString As String = "This string is immutable"
myString = "Or is it?"

In the above example, it appears that a string is created, given a value, and then has that value changed. This appears to contradict the opening statement that strings are immutable. What is actually happening is that in the first line, an instance of String is created and given the value "This string is immutable". In the second line of the example, that instance is destroyed and a new instance is created and given the value "Or is it?". The only thing that doesn't change is the name of the variable.

Unlike other intrinsic data types, String is a reference type. When a variable of reference type is passed as an argument to a function or subroutine, a reference to the memory address where the data is stored is passed instead of the actual value of the string. So in the previous example, the name of the variable remains the same, but it points to a new and different instance of the String class, which holds the new value.

See Also

String Manipulation | String Class | Char Data Type

Show:
© 2014 Microsoft