C#中获取文件大小问题

        /// <summary>
        /// 格式化文件大小
        /// </summary>
        /// <param name="filesize">文件传入大小</param>
        /// <returns></returns>
        private static string GetFileSize(long filesize)
        {
            try
            {
                if (filesize < 0)
                {
                    return "0";
                }
                else if (filesize >= 1024 * 1024 * 1024)  //文件大小大于或等于1024MB    
                {
                    return string.FORMat("{0:0.00} GB", (double)filesize / (1024 * 1024 * 1024));
                }
                else if (filesize >= 1024 * 1024) //文件大小大于或等于1024KB    
                {
                    return string.Format("{0:0.00} MB", (double)filesize / (1024 * 1024));
                }
                else if (filesize >= 1024) //文件大小大于等于1024bytes    
                {
                    return string.Format("{0:0.00} KB", (double)filesize / 1024);
                }
                else
                {
                    return string.Format("{0:0.00} bytes", filesize);
                }
            }
            catch (Exception ex)
            {
 
                throw ex;
            }
 
        }

 FileInfo t = new FileInfo(filePath);//获取文件
 文件大小 = GetFileSize(t.Length);//这样我们就获取到了文件的大小

FileInfo fileInfo = new FileInfo(filePath);
Console.WriteLine(fileInfo.Length);

static void Main(string[] args)
{
    string name = @"D:\Documents\test.zip";
    //用来获取高位数字(只有在读取超过4GB的文件才需要用到该参数)
    uint h = 0;
    //用来获取低位数据
    uint l = GetCompressedFileSize(name, ref h);
    //将两个int32拼接成一个int64
    ulong r = ((ulong)h << 32) + l;
    FileInfo fileInfo = new FileInfo(name);
    Console.WriteLine(fileInfo.Length);
    Console.WriteLine(h);
    Console.WriteLine(l);
    //最终结果
    Console.WriteLine(r);
    Console.ReadKey(true);
}
[DllImport("Kernel32.dll", CharSet = CharSet.Auto)]
private static extern uint GetCompressedFileSize(string fileName, ref uint fileSizeHigh);

static void Main(string[] args)
{
    string name = @"C:\Windows\DiagTrack\GetFileActionAllowedList.dat";
    //string name = @"D:\Documents\test.zip";
    uint h = 0;
    uint l = GetCompressedFileSize(name, ref h);
    ulong r = ((ulong)h << 32) + l;
    FileInfo fileInfo = new FileInfo(name);
    Console.WriteLine(fileInfo.Length);
    Console.WriteLine(h);
    Console.WriteLine(l);
    Console.WriteLine(r);
    ulong size = GetClusterSize("D:\\");
    if (r%size != 0)
    {
        decimal res = r / size;
        uint clu = (uint)Convert.ToInt32(Math.Ceiling(res)) + 1;
        r = size * clu;
    }
    //最终结果
    Console.WriteLine(r);
    Console.ReadKey(true);
}
//获取每簇的字节数
private static uint GetClusterSize(string rootPath)
{
    //提前声明各项参数
    uint sectorsPerCluster = 0, bytesPerSector = 0, numberOfFreeClusters = 0, totalNumberOfClusters = 0;
    GetDiskFreeSpace(rootPath, ref sectorsPerCluster, ref bytesPerSector, ref numberOfFreeClusters, ref totalNumberOfClusters);
    return bytesPerSector * sectorsPerCluster;
}
//用于获取文件实际大小的api
[DllImport("Kernel32.dll", CharSet = CharSet.Auto)]
private static extern uint GetCompressedFileSize(string fileName, ref uint fileSizeHigh);
//用于获取盘信息的api
[DllImport("kernel32.dll", CharSet = CharSet.Auto)]
private static extern bool GetDiskFreeSpace([MarshalAs(UnmanagedType.LPTStr)]string rootPathName, ref uint sectorsPerCluster, ref uint bytesPerSector, ref uint numberOfFreeClusters, ref uint totalNumbeOfClusters);

using System;
using System.ComponentModel;
using System.IO;
using System.Runtime.InteropServices;

namespace ConsoleApp1
{
    class Program
    {
        static void Main(string[] args)
        {
            string name = @"目标文件夹路径";
            uint h = 0;
            uint l = GetCompressedFileSize(name, ref h);
            if (l == uint.MaxValue)
                throw new IOException("文件读取失败。", new Win32Exception(Marshal.GetLastWin32Error()));
            ulong r = ((ulong)h << 32) + l;
            FileInfo fileInfo = new FileInfo(name);
            Console.WriteLine("文件大小：");
            Console.WriteLine(fileInfo.Length);
            Console.WriteLine("高位数据：");
            Console.WriteLine(h);
            Console.WriteLine("低位数据：");
            Console.WriteLine(l);
            Console.WriteLine("文件实际大小：");
            Console.WriteLine(r);
            ulong size = GetClusterSize("D:\\");
            if (r % size != 0)
            {
                decimal res = r / size;
                uint clu = (uint)Convert.ToInt32(Math.Ceiling(res)) + 1;
                r = size * clu;
            }
            //最终结果
            Console.WriteLine("文件占用空间：");
            Console.WriteLine(r);
            Console.ReadKey(true);
        }
        //获取每簇的字节数
        private static uint GetClusterSize(string rootPath)
        {
            //提前声明各项参数
            uint sectorsPerCluster = 0, bytesPerSector = 0, numberOfFreeClusters = 0, totalNumberOfClusters = 0;
            GetDiskFreeSpace(rootPath, ref sectorsPerCluster, ref bytesPerSector, ref numberOfFreeClusters, ref totalNumberOfClusters);
            return bytesPerSector * sectorsPerCluster;
        }
        //用于获取文件实际大小的api
        [DllImport("Kernel32.dll", CharSet = CharSet.Auto, SetLastError = true)]
        private static extern uint GetCompressedFileSize(string fileName, ref uint fileSizeHigh);
        //用于获取盘信息的api
        [DllImport("kernel32.dll", CharSet = CharSet.Auto)]
        private static extern bool GetDiskFreeSpace([MarshalAs(UnmanagedType.LPTStr)]string rootPathName, ref uint sectorsPerCluster, ref uint bytesPerSector, ref uint numberOfFreeClusters, ref uint totalNumbeOfClusters);
    }
}