【Excel】VBAマクロで文字コードを変換（utf-8やsjis）・取得・判定・一覧を作る方法【OpenFileDialog、FileSystemObject、ADODB.Stream】

Sub MojiCodeHenkanUtf8ToSjis()
    Dim hensuuFileDialog As Object
    Dim hensuuPath As Variant
    Dim hensuuStream As Object
    Dim hensuuText As String

    ' ファイルダイヤログを開く
    Set hensuuFileDialog = Application.FileDialog(3)
    hensuuFileDialog.AllowMultiSelect = True
    If hensuuFileDialog.Show = -1 Then
        For Each hensuuPath In hensuuFileDialog.SelectedItems
            ' 文字コードを取得してutf-8ならばsjisに変換
            Set hensuuStream = CreateObject("ADODB.Stream")
            hensuuStream.Open
            hensuuStream.Type = 2 'Text
            hensuuStream.Charset = "utf-8"
            hensuuStream.LoadFromFile hensuuPath
            hensuuText = hensuuStream.ReadText
            hensuuStream.Close

            hensuuStream.Open
            hensuuStream.Type = 2 'Text
            hensuuStream.Charset = "shift-jis"
            hensuuStream.WriteText hensuuText
            hensuuStream.SaveToFile hensuuPath, 2 'Overwrite
            hensuuStream.Close
        Next hensuuPath
    End If
End Sub

Function ConvertEncoding()

    Dim kaishiDialogue As FileDialog
    Set kaishiDialogue = Application.FileDialog(msoFileDialogFilePicker)
    
    With kaishiDialogue
        .Title = "ファイルを選択してください"
        .AllowMultiSelect = False
        .Filters.Add "Text Files", "*.txt", 1
        If .Show = -1 Then
            Dim fileStream As Object
            Set fileStream = CreateObject("ADODB.Stream")
            fileStream.Open
            fileStream.LoadFromFile .SelectedItems(1)
            fileStream.Charset = "Shift_JIS"
            Dim mojiretsu As String
            mojiretsu = fileStream.ReadText
            If mojiretsu.Contains("特定の文字列") Then
                fileStream.Charset = "UTF-8"
            End If
            MsgBox "ファイルの文字コードが変換されました。", vbInformation
            fileStream.SaveToFile .SelectedItems(1), 2  ' 上書き保存
            fileStream.Close
        End If
    End With
End Function

Function CreateEncodingList()

    Dim mojiCodeList As

 Workbook
    Set mojiCodeList = Workbooks.Add
    mojiCodeList.Sheets(1).Cells(1, 1).Value = "ファイル名"
    mojiCodeList.Sheets(1).Cells(1, 2).Value = "文字コード"

    Dim fso As Object, folder As Object, file As Object
    Set fso = CreateObject("Scripting.FileSystemObject")
    Set folder = fso.GetFolder("C:\YourFolder")  ' 対象フォルダを指定

    Dim rowNum As Integer
    rowNum = 2
    For Each file In folder.Files
        Dim fileStream As Object
        Set fileStream = CreateObject("ADODB.Stream")
        fileStream.Open
        fileStream.LoadFromFile file.Path
        mojiCodeList.Sheets(1).Cells(rowNum, 1).Value = file.Name
        mojiCodeList.Sheets(1).Cells(rowNum, 2).Value = fileStream.Charset
        rowNum = rowNum + 1
        fileStream.Close
    Next file

    mojiCodeList.SaveAs "C:\YourFolder\EncodingList.xlsx"
    mojiCodeList.Close False
End Function