using System;
using System.IO;

namespace ConsoleApp1
{
    class Program
    {
        static void Main(string[] args)
        {
            long length = FileSize("D:\\001.txt");
            Console.WriteLine(length);

            Console.Read();
        }

        /// <summary>
        /// 獲取, 讀取指定文件大小, 返回單位為字節
        /// </summary>
        /// <param name="path">文件路徑</param>
        /// <returns></returns>
        public static long FileSize(string path)
        {
            // 空路徑名是不合法的
            if (string.IsNullOrEmpty(path))
            {
                throw new ArgumentException("Empty path name is not legal.", "path");
            }

            // 判斷路徑是否存在
            if (!File.Exists(path))
            {
                throw new FileNotFoundException("Could not find file '" + path + "'.", path);
            }

            using (System.IO.FileStream fileStream = new System.IO.FileStream(path, System.IO.FileMode.Open, System.IO.FileAccess.Read))
            {
                return fileStream.Length;
            }
        }
    }
}