.Net C# StreamReader StreamWriter 文件读写

开发中遇到需要读写标准格式文件时，我们可以使用StreamReader和StreamWriter这两个类来完成简单高效的读取，使用起来也非常方便。使用这两个类读写文件需要注意编码格式，默认是UTF8编码，可以通过构造函数重载方法指定编码。

创建StreamReader对象实例：

StreamReader reader = new StreamReader(Path.Combine(path, fileName))

创建StreamWriter对象实例：

StreamWriter writer = new StreamWriter(Path.Combine(path, fileName))

完整参考代码：

class ReadAndWrite
    {
        public static async Task DemoMain()
        {
            string path = @"E:Test1";
            string fileName = "g.txt";
            //写入测试内容
            StringBuilder builder = new StringBuilder();
            for (int i = 0; i < 10; i++)
            {
                builder.AppendLine($"{i}--{Guid.NewGuid()}");
            }
            //目录不存在创建目录
            if (!Directory.Exists(path))
            {
                Directory.CreateDirectory(path);
            }

            await WriteTextAsync(path, fileName, builder);
            await ReadTextAsync(path, fileName);
        }
        /// 

        /// 向指定文件中写入内容
        /// 
        /// 目标文件目录
        /// 目标文件名称
        /// 写入内容
        /// 
        static async Task WriteTextAsync(string path, string fileName, StringBuilder stringBuilder)
        {
            Encoding.RegisterProvider(CodePagesEncodingProvider.Instance);
            using (StreamWriter writer = new StreamWriter(Path.Combine(path, fileName), true, Encoding.GetEncoding("GBK")))
            {
                using (StringReader reader = new StringReader(stringBuilder.ToString()))
                {
                    string readText;
                    while ((readText = await reader.ReadLineAsync()) != null)
                    {
                        await writer.WriteLineAsync(readText);
                    }
                }
            }
        }
        /// 

        /// 读取文件内容并输出至控制台
        /// 
        /// 
        /// 
        /// 
        static async Task ReadTextAsync(string path, string fileName)
        {
            using (StreamReader reader = new StreamReader(Path.Combine(path, fileName)))
            {
                string line;
                while ((line = await reader.ReadLineAsync()) != null)
                {
                    Console.WriteLine(line);
                }
            }
        }

    }

输出结果：

注意：.Net Core 以后默认不支持 GBK、GB2312等编码，需要添加System.Text.Encoding.CodePages 包后使用。

//按装System.Text.Encoding.CodePages包后加入如下代码
Encoding.RegisterProvider(CodePagesEncodingProvider.Instance);