C# Win32 APIを使ってバイトの単位を変換する

C#でWin APIのShell Lightweight Utility Functionsを用いてバイトの単位を変換する補助関数のコードです。拡張メソッドとして定義していますが、thisを外せば関数として利用することもできます。this UInt64 value等のUInt64部分を変更することで対応する型を増やすことができます。

StrFormatByteSizeExWの対応バージョンがWindows Vista with SP1 [desktop apps only]＆Shlwapi.dll (version 6.0 or later)、StrFormatByteSizeWの対応バージョンがWindows 2000 Professional, Windows XP [desktop apps only]＆Shlwapi.dll (version 4.71 or later)で後者の方が対応範囲が広いことから、フラグなしバージョンはStrFormatByteSizeWを利用しています。

// StringByteFormatExtensions.cs
using System;
using System.ComponentModel;
using System.Runtime.InteropServices;
using System.Security;
using System.Security.Permissions;
using System.Text;

namespace Potisan.Windows.ByteFormat
{
    [SecurityPermission(SecurityAction.LinkDemand, UnmanagedCode=true)]
    public static class StringByteFormatExtensions
    {
        [SuppressUnmanagedCodeSecurity]
        private static class NativeMethods
        {
            [DllImport("shlwapi.dll", SetLastError = true,
                CharSet = CharSet.Unicode, CallingConvention = CallingConvention.StdCall)]
            public static extern IntPtr StrFormatByteSizeW(
                Int64 qdw,
                StringBuilder pszBuf,
                UInt32 cchBuf);
            [DllImport("shlwapi.dll", SetLastError = true,
                CharSet = CharSet.Unicode, CallingConvention = CallingConvention.StdCall)]
            public static extern IntPtr StrFormatByteSizeExW(
                UInt64 qdw,
                StrFormatByteSizeExFlags flags,
                StringBuilder pszBuf,
                UInt32 cchBuf);
        }

        private const int ERROR_INSUFFICIENT_BUFFER = 122;

        [Flags]
        public enum StrFormatByteSizeExFlags
        {
            RoundToNearestDisplayedDigit = 1,
            TruncateUndisplayedDEcimalDigits = 2,
        }

        public static String FormatByteSize(this Int64 value, int expanding = 256)
        {
            StringBuilder buffer = new StringBuilder(expanding);
            while (NativeMethods.StrFormatByteSizeW(
                value, buffer,
                checked((uint)buffer.Capacity)) != IntPtr.Zero
                && buffer.Length + 1 == buffer.Capacity)
            {
                buffer.Capacity += expanding;
            }
            if (Marshal.GetLastWin32Error() != 0)
                throw new Win32Exception();
            return buffer.ToString();
        }
        public static String FormatByteSize(this Int32 value, int expanding = 256)
        {
            return FormatByteSize((Int64)value, expanding);
        }
        public static String FormatByteSize(this UInt32 value, int expanding = 256)
        {
            return FormatByteSize((Int64)value, expanding);
        }
        public static String FormatByteSize(this UInt64 value, int expanding = 256)
        {
            return FormatByteSize((Int64)value, expanding);
        }

        public static String FormatByteSize(this UInt64 value, StrFormatByteSizeExFlags flags, int expanding = 256)
        {
            StringBuilder buffer = new StringBuilder(expanding);
            while (NativeMethods.StrFormatByteSizeExW(
                value, flags, buffer,
                checked((uint)buffer.Capacity)) != IntPtr.Zero
                && buffer.Length + 1 == buffer.Capacity)
            {
                buffer.Capacity += expanding;
            }
            if (Marshal.GetLastWin32Error() != 0)
                throw new Win32Exception();
            return buffer.ToString();
        }
        public static String FormatByteSize(this UInt32 value, StrFormatByteSizeExFlags flags, int expanding = 256)
        {
            return FormatByteSize((UInt64)value, flags, expanding);
        }
        public static String FormatByteSize(this Int32 value, StrFormatByteSizeExFlags flags, int expanding = 256)
        {
            return FormatByteSize((UInt64)value, flags, expanding);
        }
        public static String FormatByteSize(this Int64 value, StrFormatByteSizeExFlags flags, int expanding = 256)
        {
            return FormatByteSize((UInt64)value, flags, expanding);
        }
    }
}

using System.Text;
using System.Windows.Forms;
using Potisan.Windows.ByteFormat;

namespace VolumeDeviceIoControl1
{
    static class Program
    {
        static void Main()
        {
            StringBuilder builder = new StringBuilder();

            long i = 12345678910;
            builder.AppendLine(i.FormatByteSize());
            builder.AppendLine(i.FormatByteSize(
                StringByteFormatExtensions.StrFormatByteSizeExFlags.RoundToNearestDisplayedDigit));

            // 11.4 GB
            // 11.5 GB
            MessageBox.Show(builder.ToString());
        }
    }
}

2021/3/10：この記事は別のブログで投稿した記事を移動したものです。