VB.NET 文字列を数値に変換する

文字列を数値に変換する方法には、幾つかの方法があり、 Parse()メソッド・TryParse()メソッド・Convertクラスなどがあります。

ブール（Boolean）文字列をブール値に変換する

Public Shared Overloads Function ToBoolean(ByVal str As String) As Boolean
    Dim val As Boolean

    Try
        val = Boolean.Parse(str)
    Catch ex As System.FormatException
        val = False
    End Try

    Return val
End Function

Public Shared Overloads Function ToBoolean(ByVal obj As Object) As Boolean
    Return ToBoolean(obj.ToString())
End Function

TryParseを使用する方法

Dim str As String = "23456"

Dim bResult As Boolean
bc = Boolean.TryParse(str, bResult)

 

文字列を数値に変換する

'整数型Long
Public Shared Overloads Function ToLong(ByVal str As String) As Long
    Dim val As Long

    Try
        val = Long.Parse(str)
    Catch ex As System.FormatException
        val = 0
    End Try

    Return val
End Function

Public Shared Overloads Function ToLong(ByVal obj As Object) As Long
    Return ToLong(obj.ToString())
End Function

'整数型Short
Public Shared Overloads Function ToShort(ByVal str As String) As Short
    Return CType(ToLong(str), Short)
End Function

Public Shared Overloads Function ToShort(ByVal obj As Object) As Short
    Return CType(ToLong(obj.ToString()), Short)
End Function

'整数型Integer
Public Shared Overloads Function ToInteger(ByVal str As String) As Integer
    Return CType(ToLong(str), Integer)
End Function

Public Shared Overloads Function ToInteger(ByVal obj As Object) As Integer
    Return CType(ToLong(obj.ToString()), Integer)
End Function


'実数型Decimal
Public Shared Overloads Function ToDecimal(ByVal str As String) As Decimal
    Dim val As Decimal

    Try
        val = Decimal.Parse(str)
    Catch ex As System.FormatException
        val = 0
    End Try

    Return val
End Function

Public Shared Overloads Function ToDecimal(ByVal obj As Object) As Decimal
    Return ToDecimal(obj.ToString())
End Function


'実数型Double
Public Shared Overloads Function ToDouble(ByVal str As String) As Double
    Dim val As Double

    Try
        val = Double.Parse(str)
    Catch ex As System.FormatException
        val = 0
    End Try

    Return val
End Function

Public Shared Overloads Function ToDouble(ByVal obj As Object) As Double
    Return ToDouble(obj.ToString())
End Function

TryParseを使用する方法

Dim str As String = "23456"

Dim iResult As Integer
bc = Integer.TryParse(str, System.Globalization.NumberStyles.Number, _
	                   System.Globalization.CultureInfo.InvariantCulture, iResult)

Dim lResult As Long
bc = Long.TryParse(str, System.Globalization.NumberStyles.Number, _
	                System.Globalization.CultureInfo.InvariantCulture, lResult)

Dim dResult As Double
bc = Double.TryParse(str, System.Globalization.NumberStyles.Any, _
	                  System.Globalization.CultureInfo.InvariantCulture, dResult)


Dim mResult As Decimal
bc = Decimal.TryParse(str, System.Globalization.NumberStyles.Any, _
	                   System.Globalization.CultureInfo.InvariantCulture, mResult)

 

16進数文字列の数値変換する

変換にはConvert クラスを使用します。

Public Shared Overloads Function HexStrToLong(ByVal str As String) As Long
    Dim val As Long

    Try
        val = Convert.ToInt64(str, 16)
    Catch ex As System.FormatException
        val = 0
    End Try

    Return val
End Function

Public Shared Overloads Function HexStrToLong(ByVal obj As Object) As Long
    Return HexStrToLong(obj.ToString())
End Function

TryParseを使用する方法

Dim sResult As Short

bc = Short.TryParse("ABCD", System.Globalization.NumberStyles.HexNumber, _
	                    System.Globalization.CultureInfo.InvariantCulture, sResult)

 

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Parse・ TryParseはNumberStyles列挙体を使用することにより文字列のスタイルを変えられます。

'桁の区切り記号が含まれている
Dim val1 As Integer = Integer.Parse("123,456,789", _
                      System.Globalization.NumberStyles.AllowThousands)

または

Dim val1 As Integer = Integer.Parse("123,456,789", _
                      System.Globalization.NumberStyles.AllowThousands, _
                      System.Globalization.CultureInfo.InvariantCulture)


'指数表記を使用する
Dim val2 As Integer = Integer.Parse("123e4", _
                      System.Globalization.NumberStyles.AllowExponent)


'通貨記号が含まれている場合
Dim val3 As Integer = Integer.Parse("\123456", _
                      System.Globalization.NumberStyles.AllowCurrencySymbol)

※Parse()・TryParse()の文字列の解釈はWindowsの地域設定のコントロールパネルの設定に影響されます。

・地域設定の影響を受けないようにするにはCultureInfoクラスを明示的に指定することです

・TryParse()は数値のオーバーフローのエラーは出しません。