c#连续读取文件 [英] c# continuously read file

问题描述

我想像 GNU tail 一样使用-f"参数连续读取文件.我需要它来实时读取日志文件.正确的做法是什么?

I want to read file continuously like GNU tail with "-f" param. I need it to live-read log file. What is the right way to do it?

推荐答案

您想以二进制模式打开 FileStream.定期查找文件末尾减去 1024 字节(或其他)，然后读取到末尾并输出.这就是 tail -f 的工作原理.

You want to open a FileStream in binary mode. Periodically, seek to the end of the file minus 1024 bytes (or whatever), then read to the end and output. That's how tail -f works.

回答您的问题:

二进制，因为如果您将其作为文本阅读，则很难随机访问该文件.您必须自己进行二进制到文本的转换，但这并不困难.(见下文)

Binary because it's difficult to randomly access the file if you're reading it as text. You have to do the binary-to-text conversion yourself, but it's not difficult. (See below)

1024 字节，因为这是一个非常方便的数字，应该可以处理 10 或 15 行文本.通常.

1024 bytes because it's a nice convenient number, and should handle 10 or 15 lines of text. Usually.

以下是打开文件、读取最后 1024 个字节并将其转换为文本的示例:

Here's an example of opening the file, reading the last 1024 bytes, and converting it to text:

static void ReadTail(string filename)
{
    using (FileStream fs = File.Open(filename, FileMode.Open, FileAccess.Read, FileShare.ReadWrite))
    {
        // Seek 1024 bytes from the end of the file
        fs.Seek(-1024, SeekOrigin.End);
        // read 1024 bytes
        byte[] bytes = new byte[1024];
        fs.Read(bytes, 0, 1024);
        // Convert bytes to string
        string s = Encoding.Default.GetString(bytes);
        // or string s = Encoding.UTF8.GetString(bytes);
        // and output to console
        Console.WriteLine(s);
    }
}

请注意，您必须使用 FileShare.ReadWrite 打开，因为您正在尝试读取当前打开以供另一个进程写入的文件.

Note that you must open with FileShare.ReadWrite, since you're trying to read a file that's currently open for writing by another process.

另请注意，我使用了 Encoding.Default，它在美国/英语和大多数西欧语言中将是 8 位字符编码.如果文件以某种其他编码(如 UTF-8 或其他 Unicode 编码)编写，则字节可能无法正确转换为字符.如果您认为这将是一个问题，则必须通过确定编码来处理该问题.搜索堆栈溢出以获取有关确定文件文本编码的信息.

Also note that I used Encoding.Default, which in US/English and for most Western European languages will be an 8-bit character encoding. If the file is written in some other encoding (like UTF-8 or other Unicode encoding), It's possible that the bytes won't convert correctly to characters. You'll have to handle that by determining the encoding if you think this will be a problem. Search Stack overflow for info about determining a file's text encoding.

如果您想定期执行此操作(例如，每 15 秒一次)，您可以设置一个计时器，根据需要随时调用 ReadTail 方法.您可以通过在程序开始时只打开一次文件来优化一些东西.这取决于你.

If you want to do this periodically (every 15 seconds, for example), you can set up a timer that calls the ReadTail method as often as you want. You could optimize things a bit by opening the file only once at the start of the program. That's up to you.

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