VB.Net Tutorial/Data Type/String Functions
Содержание
- 1 CStr: Convert Double to String
- 2 Duplicate a string
- 3 Format: c
- 4 Get string index by using InStr
- 5 Instr
- 6 Instr: find character in a string
- 7 Instr: find sub string a in a string
- 8 IsDBNull
- 9 IsNumeric, IsDate, IsNothing
- 10 LCase: change string to lower case
- 11 Left: get characters from left
- 12 Len: get string length
- 13 Microsoft.VisualBasic.Left
- 14 Mid(string, 4, 5): get sub string from middle
- 15 Mid(string, 7): get sub string from start
- 16 Passing formatted numeric values to Val
- 17 Passing String values to Val
- 18 Right: get characters from right
- 19 String.Copy
- 20 String handling function: Len
- 21 UCase: change string to upper case
- 22 Use String.Concat to concatenate two strings
CStr: Convert Double to String
<source lang="vbnet">Public Class Tester
Public Shared Sub Main Dim x As Double x = 12345678901234567890D Console.WriteLine(CStr(x))
End Sub
End Class</source>
1.23456789012346E+19
Duplicate a string
<source lang="vbnet">Public Class Tester
Public Shared Sub Main Console.WriteLine(StrDup(30, "-")) End Sub
End Class</source>
------------------------------
Format: c
<source lang="vbnet">Public Class Tester
Public Shared Sub Main Console.WriteLine( Format(123, "c") ) End Sub
End Class</source>
$123.00
Get string index by using InStr
<source lang="vbnet">Class Tester
Shared Sub Main() Dim userInput As String userInput = " asdf " Console.WriteLine(InStr(userInput, "f")) End Sub
End Class</source>
6
Instr
<source lang="vbnet">Public Class Tester
Public Shared Sub Main Dim MyString As String, YourString As String MyString = "asdf" YourString = "fdsa" Console.WriteLine(InStr(2, MyString, YourString)) End Sub
End Class</source>
0
Instr: find character in a string
<source lang="vbnet">Module Tester
Public Sub Main() Dim sHello As String = "Hello World" Console.WriteLine("Original string: {0}", sHello) Console.WriteLine("Find character (Instr(1, sHello, "l")) : {0}", InStr(1, sHello, "l")) End Sub
End Module</source>
Original string: Hello World Find character (Instr(1, sHello, "l")) : 3
Instr: find sub string a in a string
<source lang="vbnet">Module Tester
Public Sub Main() Dim sHello As String = "Hello World" Console.WriteLine("Original string: {0}", sHello) Console.WriteLine("Find substring (Instr(1, sHello, "World")) : {0}", InStr(1, sHello, "Wor
ld"))
End Sub
End Module</source>
Original string: Hello World Find substring (Instr(1, sHello, "World")) : 7
IsDBNull
<source lang="vbnet">Public Module modMain
Public Sub Main() Dim title As String = "Mr." Dim name As Object = DBNull.Value Dim addressLine1 As String = title & " " & name If IsDBNull(addressLine1) Then Console.WriteLine("Null value") Else Console.WriteLine(addressLine1) End If End Sub
End Module</source>
Mr.
IsNumeric, IsDate, IsNothing
<source lang="vbnet">Public Class Tester
Public Shared Sub Main Dim theData As String = Nothing Dim result As New System.Text.StringBuilder " ----- Format nothing. result.AppendLine(String.Format( _ "IsNumeric({0}) ... {1}", theData, IsNumeric(theData))) result.AppendLine(String.Format( _ "IsDate({0}) ... {1}", theData, IsDate(theData))) result.AppendLine(String.Format( _ "IsNothing({0}) ... {1}", theData, IsNothing(theData))) result.AppendLine() " ----- Format a number in a string. theData = "-12.345" result.AppendLine(String.Format( _ "IsNumeric({0}) ... {1}", theData, IsNumeric(theData))) result.AppendLine(String.Format( _ "IsDate({0}) ... {1}", theData, IsDate(theData))) result.AppendLine(String.Format( _ "IsNothing({0}) ... {1}", theData, IsNothing(theData))) result.AppendLine() " ----- Format a date in a string. theData = "July 17, 2007" result.AppendLine(String.Format( _ "IsNumeric({0}) ... {1}", theData, IsNumeric(theData))) result.AppendLine(String.Format( _ "IsDate({0}) ... {1}", theData, IsDate(theData))) result.Append(String.Format( _ "IsNothing({0}) ... {1}", theData, IsNothing(theData))) Console.WriteLine(result.ToString()) End Sub
End Class</source>
IsNumeric() ... False IsDate() ... False IsNothing() ... True IsNumeric(-12.345) ... True IsDate(-12.345) ... False IsNothing(-12.345) ... False IsNumeric(July 17, 2007) ... False IsDate(July 17, 2007) ... True IsNothing(July 17, 2007) ... False
LCase: change string to lower case
<source lang="vbnet">Module Tester
Public Sub Main() Dim sHello As String = "Hello World" Console.WriteLine("Original string: {0}", sHello) Console.WriteLine("Lowercase (LCase(sHello)) : {0}", LCase(sHello)) End Sub
End Module</source>
Original string: Hello World Lowercase (LCase(sHello)) : hello world
Left: get characters from left
<source lang="vbnet">Module Tester
Public Sub Main() Dim sHello As String = "Hello World" Console.WriteLine("Original string: {0}", sHello) Console.WriteLine("Leftmost two characters (Left(sHello, 2)): {0}", Left(sHello, 2)) End Sub
End Module</source>
Original string: Hello World Leftmost two characters (Left(sHello, 2)): He
Len: get string length
<source lang="vbnet">Public Class Tester
Public Shared Sub Main Console.WriteLine(Len("txtString1.Text")) End Sub
End Class</source>
15
Microsoft.VisualBasic.Left
<source lang="vbnet">public class Test
public Shared Sub Main Dim strName As String = "Visual Basic Express" If Microsoft.VisualBasic.Left(strName, 3) = "Vis" Then Console.WriteLine("True") If strName.StartsWith("Vis") Then Console.WriteLine("True") End Sub
End class</source>
True True
Mid(string, 4, 5): get sub string from middle
<source lang="vbnet">Module Tester
Public Sub Main() Dim sHello As String = "Hello World" Console.WriteLine("Original string: {0}", sHello) Console.WriteLine("From middle of string (Mid(sHello, 4, 5)): {0}", Mid(sHello, 4, 5)) End Sub
End Module</source>
Original string: Hello World From middle of string (Mid(sHello, 4, 5)): lo Wo
Mid(string, 7): get sub string from start
<source lang="vbnet">Module Tester
Public Sub Main() Dim sHello As String = "Hello World" Console.WriteLine("Original string: {0}", sHello) Console.WriteLine("Starting with character (Mid(sHello, 7)): {0}", Mid(sHello, 7)) End Sub
End Module</source>
Original string: Hello World Starting with character (Mid(sHello, 7)): World
Passing formatted numeric values to Val
<source lang="vbnet">Option Strict On Public Module Tester
Public Sub Main() " Passing formatted numeric values to Val Console.WriteLine(Val("$1034.51")) Console.WriteLine(Val("1,032.54")) End Sub
End Module</source>
0 1
Passing String values to Val
<source lang="vbnet">Option Strict On Public Module Tester
Public Sub Main() " Console.WriteLine(Val("913.3")) Console.WriteLine(Val("131AC57")) Console.WriteLine(Val("-132.23")) Console.WriteLine(Val("+1203.22")) Console.WriteLine(Val("A0545")) Console.WriteLine() End Sub
End Module</source>
913.3 131 -132.23 1203.22 0
Right: get characters from right
<source lang="vbnet">Module Tester
Public Sub Main() Dim sHello As String = "Hello World" Console.WriteLine("Original string: {0}", sHello) Console.WriteLine("Rightmost four characters (Right(sHello, 4)): {0}", Right(sHello, 4)) End Sub
End Module</source>
Original string: Hello World Rightmost four characters (Right(sHello, 4)): orld
String.Copy
<source lang="vbnet">public class Test
public Shared Sub Main Dim str1, str2 As String str1 = "some text" str2 = str1 str2 = String.Copy(str1) Console.WriteLine(str1 & vbCrLf & str2) End Sub
End class</source>
some text some text
String handling function: Len
<source lang="vbnet">Module Tester
Public Sub Main() Dim sHello As String = "Hello World" Console.WriteLine("Original string: {0}", sHello) Console.WriteLine("Length of string (Len(sHello)): {0}", Len(sHello)) End Sub
End Module</source>
Original string: Hello World Length of string (Len(sHello)): 11
UCase: change string to upper case
<source lang="vbnet">Module Tester
Public Sub Main() Dim sHello As String = "Hello World" Console.WriteLine("Original string: {0}", sHello) Console.WriteLine("Uppercase (UCase(sHello)) : {0}", UCase(sHello)) End Sub
End Module</source>
Original string: Hello World Uppercase (UCase(sHello)) : HELLO WORLD
Use String.Concat to concatenate two strings
<source lang="vbnet">public class Test
public Shared Sub Main Dim aryStrings() As String = {"string1", "string2", "string3", "string4"} Dim strLongString As String strLongString = String.Concat(aryStrings) Console.WriteLine(strLongString) End Sub
End class</source>
string1string2string3string4