将文件大小转换为文本表示

Question

我正在构建在线文件管理器。它显示的列之一是文件大小，但这总是很大的字节数。我想像 Windows Explorer 一样显示文件大小，使用较小的数字和适当的单位，例如5 MB 而不是 5000000。

这对我来说一点也不难，但我想知道 Windows 而不是有一个内置函数来执行此操作。已经有东西了吗，还是我必须自己动手？

Answer 1

我看到 3 个变体：

function FormatFileSize(const ASize: UInt64; AKbMode: Boolean): UnicodeString;
var
  PS: IPropertySystem;
  PD: IPropertyDescription;
  PV: TPropVariant;
  Flags: DWORD;
  Display: PWideChar;
  PUI: IPropertyUI;
begin
  Result := '';

  // Variant 1
  if Succeeded(CoCreateInstance(CLSID_IPropertySystem, nil, CLSCTX_INPROC_SERVER, IPropertySystem, PS)) then
    begin
      if Succeeded(PS.GetPropertyDescription(PKEY_Size, IPropertyDescription, PD)) then
        begin
          PV.vt := VT_UI8;
          PV.uhVal.QuadPart := ASize;
          if AKbMode then Flags := PDFF_ALWAYSKB
                     else Flags := PDFF_DEFAULT;
          if Succeeded(PD.FormatForDisplay(PV, Flags, Display)) then
             begin
               Result := Display;
               CoTaskMemFree(Display);
             end;
          PD := nil;
        end;
      PS := nil;
    end;
  if Result <> '' then Exit;

  // Variant 2 - Windows XP mode, can be replaced with Variant 3
  if Succeeded(CoCreateInstance(CLSID_PropertiesUI, nil, CLSCTX_INPROC_SERVER, IPropertyUI, PUI)) then
    begin
      PV.vt := VT_UI8;
      PV.uhVal.QuadPart := ASize;
      SetLength(Result, 100);
      if Succeeded(PUI.FormatForDisplay(PKEY_Size.fmtid, PKEY_Size.pid, PV, PUIFFDF_DEFAULT, PWideChar(Result), Length(Result) + 1)) then
        Result := PWideChar(Result)
      else
        Result := '';
      PUI := nil;
    end;
  if Result <> '' then Exit;

  // Variant 3
  SetLength(Result, 100);
  if AKbMode then
    Result := StrFormatKBSizeW(ASize, PWideChar(Result), Length(Result))
  else
    Result := StrFormatByteSizeW(ASize, PWideChar(Result), Length(Result));
end;

Answer 2

这是 C# 中的两个变体（它们需要 Windows Vista）：

...
Console.WriteLine(FormatByteSize(1031023120)); // 983 MB
Console.WriteLine(FormatByteSize2(1031023120, true)); // 1 006 859 KB
...

请注意使用 Windows 的好处（或不便之处，具体取决于您的看法）是您将获得使用 Shell/OS 文化的本地化版本（如果有的话）。

public static string FormatByteSize2(long size, bool alwaysKb = false)
{
    // Here, we use Windows Shell's size column definition and formatting
    // note although System.Size is defined as a UInt64, formatting doesn't support more than long.MaxValue...
    PSGetPropertyKeyFromName("System.Size", out var pk);
    var pv = new PROPVARIANT(size);
    var sb = new StringBuilder(128);
    const int PDFF_ALWAYSKB = 4;
    PSFormatForDisplay(ref pk, pv, alwaysKb ? PDFF_ALWAYSKB : 0, sb, sb.Capacity);
    return sb.ToString();
}

public static string FormatByteSize(long size)
{
    // Here, we use use a Windows Shell API (probably the sames algorithm underneath)
    // It's much simpler, we only need to declare one StrFormatByteSizeW API
    var sb = new StringBuilder(128);
    StrFormatByteSizeW(size, sb, sb.Capacity);
    return sb.ToString();
}

[DllImport("shlwapi", CharSet = CharSet.Unicode)]
private static extern IntPtr StrFormatByteSizeW(long qdw, [MarshalAs(UnmanagedType.LPWStr)] StringBuilder pszBuf, int cchBuf);

[DllImport("propsys", CharSet = CharSet.Unicode)]
private static extern int PSFormatForDisplay(
    ref PROPERTYKEY propkey,
    PROPVARIANT pv,
    int pdfFlags,
    [MarshalAs(UnmanagedType.LPWStr)] StringBuilder pszBuf, int cchBuf);

[DllImport("propsys", CharSet = CharSet.Unicode)]
private static extern int PSGetPropertyKeyFromName([MarshalAs(UnmanagedType.LPWStr)] string pszName, out PROPERTYKEY ppropkey);

[StructLayout(LayoutKind.Sequential)]
private struct PROPERTYKEY
{
    public Guid fmtid;
    public int pid;
}

[StructLayout(LayoutKind.Sequential)]
private class PROPVARIANT
{
    // note this version of PROPVARIANT is far from being suited for all purposes...
    public short vt;
    short wReserved1;
    short wReserved2;
    short wReserved3;
    public long val;

    const short VT_UI8 = 21;

    public PROPVARIANT(long ul)
    {
        wReserved3 = wReserved2 = wReserved1 = 0;
        val = ul;
        vt = VT_UI8;
    }
}

将文件大小转换为文本表示

Transforming file sizes to text representation

windows

text

formatting

string-formatting

windows-explorer