只读取 .txt 文件中的最后一个字符 [英] Only read the last character in a .txt file

问题描述

我正在使用读取txt文件并将结果发送到arduino的处理来创建程序.我可以让它发送字符串并保持更新，但是一旦我尝试只发送最后一个字符，它就行不通了……任何人都可以帮我解决这个问题吗?基本上我需要从 txt 文件中读取最后一个字符，并通过串行将其作为字符发送到 arduino、python 或处理两者都可以工作！

I am creating a program using processing that read txt file and send the result to the arduino. I can get it to send string and keep update, but as soon as I try to just send the last char it won't work... Can anyone help me with this? Basically I need to read the last char from a txt file and send it as char through serial to arduino, python or processing both will work!

*这是我的代码 [正在处理]

*Here is my code [ Processing ]

import processing.serial.*;
import java.io.*;

int mySwitch=0;
int counter=0;
String [] subtext;
Serial myPort;
   
void setup(){
   //Create a switch that will control the frequency of text file reads.
   //When mySwitch=1, the program is setup to read the text file.
   //This is turned off when mySwitch = 0
   mySwitch=1;
 
   //Open the serial port for communication with the Arduino
   //Make sure the COM port is correct
   myPort = new Serial(this, "COM4", 9600);
   myPort.bufferUntil('\n');
}

void draw() {
   if (mySwitch>0){
       /*The readData function can be found later in the code. This is the call to read a CSV file on the computer hard-drive. */
       readData("G:/Personal/control.txt");
 
       /*The following switch prevents continuous reading of the text file, until   we are ready to read the file again. */
       mySwitch=0;
   }

   /*Only send new data. This IF statement will allow new data to be sent to the arduino. */
   if(counter<subtext.length){
       /* Write the next number to the Serial port and send it to the Arduino There will be a delay of half a second before the command is sent to turn the LED off : myPort.write('0'); */
       myPort.write(subtext[counter]);
       delay(500);
       myPort.write('0');
       delay(100);

       //Increment the counter so that the next number is sent to the arduino.
       counter++;
   } else{
       //If the text file has run out of numbers, then read the text file again in 5 seconds.
       delay(5000);
       mySwitch=1;
   }
} 


/* The following function will read from a CSV or TXT file */
void readData(String myFileName){
 
 File file=new File(myFileName);
 BufferedReader br=null;
 
 try{
   br=new BufferedReader(new FileReader(file));
   String text=null;
 
   /* keep reading each line until you get to the end of the file */
 while((text=br.readLine())!=null){
   * Spilt each line up into bits and pieces using a comma as a separator */

   subtext = splitTokens(text,",");
 }
 }catch(FileNotFoundException e){
     e.printStackTrace();
 }catch(IOException e){
     e.printStackTrace();
 }finally{
     try {
        if (br != null){
           br.close();
        }
     } catch (IOException e) {
     e.printStackTrace();
   }
 }

这是我正在处理的数据

[19:54:57] [服务器线程/信息]:[@] b

[19:54:57] [Server thread/INFO]: [@] b

[19:54:57] [服务器线程/信息]:[@] a

[19:54:57] [Server thread/INFO]: [@] a

[19:54:57] [服务器线程/信息]:[@] b

[19:54:57] [Server thread/INFO]: [@] b

[19:54:57] [服务器线程/信息]:[@] a

[19:54:57] [Server thread/INFO]: [@] a

[19:54:58] [服务器线程/信息]:[@] b

[19:54:58] [Server thread/INFO]: [@] b

[19:54:58] [服务器线程/信息]:[@] a

[19:54:58] [Server thread/INFO]: [@] a

[19:54:59] [服务器线程/信息]:[@] b

[19:54:59] [Server thread/INFO]: [@] b

[20:30:23] [服务器线程/INFO]:[@] a

[20:30:23] [Server thread/INFO]: [@] a

[20:30:24] [服务器线程/信息]:[@] b

[20:30:24] [Server thread/INFO]: [@] b

[21:07:34] [服务器线程/INFO]:[@] a

[21:07:34] [Server thread/INFO]: [@] a

[21:07:35] [服务器线程/信息]:[@] b

[21:07:35] [Server thread/INFO]: [@] b

• 我真正关心的唯一值是 a/b
• 此文件将始终以这种格式更新

推荐答案

从文件中读取最后一个字符:

Reading the last character from a file:

with open(filename, 'rb+') as f:
    f.seek(f.tell()-1,2)    # f.seek(0,2) is legal for last char in both python 2 and 3 though
    print f.read()

对于 Python 3
为了使它更通用，我们想在不打开二进制模式的情况下读取文件的倒数第二个(可以是任何字符):

For Python 3
To make it more generic say we want to read second last (can be any though) char of the file without turning on the binary mode:

with open('file.txt', 'r') as f:
    f.seek(0, 2)
    # seek to end of file; f.seek(0, os.SEEK_END) is legal

    f.seek(f.tell() - 2, 0)
    # seek to the second last char of file;
    # while f.seek(f.tell()-2, os.SEEK_SET) is legal,
    # f.seek(-2, 0) will throw an error.

    print(f.read())

seek 是一个文件对象处理注释

Seek is a file object handling comment

file.seek(offset,position)

1. offset:您需要多少个字符(即 1 表示一个字符)
2. position:告诉你的文件读/写操作应该从哪里开始.
   • 0 表示文件开始
   • 1 表示文件读/写光标的当前位置
   • 2 表示文件结束
1. offset: How many characters you need (i.e. 1 means one character)
2. position: Tell where your file read/write operation should start .
   • 0 means starting of file
   • 1 means current position of file read/write cursor
   • 2 means end of file

f.seek(f.tell()-1,2) 表示到文件末尾并往回遍历一个元素

f.seek(f.tell()-1,2) means go to the end of file and traverse back one element

print f.read() 打印从seek命令获得的值

print f.read() prints the value obtained from the seek command

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