using System;

namespace DemoConsole
{
    class Program
    {
        static void Main(string[] args)
        {
            // base64字符串
            string base64Str = "";
            byte[] bytes = Convert.FromBase64String(base64Str);

            // 寫入文件到指定位置
            using (System.IO.FileStream fs = new System.IO.FileStream("D:\\001.jpg", System.IO.FileMode.Create, System.IO.FileAccess.Write))
            {
                fs.Write(bytes, 0, bytes.Length);
                fs.Flush();
            }
        }
    }
}