我正在创建一个使用处理读取txt文件并将结果发送到arduino的程序。 我可以让它发送字符串并保持更新，但是一旦我尝试发送最后一个字符，它就不起作用......任何人都可以帮助我吗？基本上我需要从 txt 文件中读取最后一个字符，并将其作为字符通过串行发送到 arduino、python 或处理两者都可以！
*这是我的代码[正在处理]
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] [服务器线程/信息]：[@] a
[19:54:57] [服务器线程/信息]：[@] b
[19:54:57] [服务器线程/信息]：[@] a
[19:54:58] [服务器线程/信息]：[@] b
[19:54:58] [服务器线程/信息]：[@] a
[19:54:59] [服务器线程/信息]：[@] b
[20:30:23] [服务器线程/信息]：[@] a
[20:30:24] [服务器线程/信息]：[@] b
[21:07:34] [服务器线程/信息]：[@] a
[21:07:35] [服务器线程/信息]：[@] b
从文件中读取最后一个字符：
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
为了使其更通用，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（可以是任意）字符：
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 是处理注释的文件对象
file.seek(offset,position)offsetpositionf.seek(f.tell()-1,2)print f.read()Stefan 的回答很简单，也很有效，但没有考虑文本文件：
vimgedit如果文本文件包含非英语字符，则到目前为止提供的答案都不起作用。
下面的示例可以解决这两个问题。
import os
def get_last_utf8_char(filename, ignore_newlines=True):
"""
Reads the last character of a UTF-8 text file.
:param filename: The path to the text file to read
:param ignore_newlines: Set to true, if the newline character at the end of the file should be ignored
:return: Returns the last UTF-8 character in the file or None, if the file is empty
"""
with open(filename, 'rb') as f:
last_char = None
# Reads last 4 bytes, as the maximum size of an UTF-8 character is 4 bytes
num_bytes_to_read = 4
# If ignore_newlines is True, read two more bytes, as a newline character
# can be up to 2 bytes (eg. \r\n)
# and we might have a newline character at the end of file
# or size bytes, if file's size is less than 4 bytes
if ignore_newlines:
num_bytes_to_read += 2
size = os.fstat(f.fileno()).st_size
f.seek(-min(num_bytes_to_read, size), os.SEEK_END)
last_bytes = f.read()
# Find the first byte of a UTF-8 character, starting
# from the last byte
offset = -1
while abs(offset) <= len(last_bytes):
b = last_bytes[offset]
if ignore_newlines and b in b'\r\n':
offset -= 1
continue
if b & 0b10000000 == 0 or b & 0b11000000 == 0b11000000:
# If this is first byte of a UTF8 character,
# interpret this and all bytes after it as UTF-8
last_char = last_bytes[offset:].decode('utf-8')
break
offset -= 1
if last_char and ignore_newlines:
last_char = last_char.replace('\r', '').replace('\n', '')
return last_char
工作原理：
示例文本文件 -
bg.txtЗдравей свят
使用方法：
>>> get_last_utf8_char('bg.txt')
т
这适用于 UTF-8 和 ASCII 编码文件。
我做了什么：
将其转换为字符串并读取最后一个字符并打印出来。
a=open('does&donts.txt','rb')
lines = a.readlines()
a.close()
if lines:
last_line = lines[-1]
print last_line
b="".join(last_line)
print b[-1:]
希望有帮助
只需使用这个：
with open("file.txt", "r") as f:
file_str = str(f.read())
f.close()
last_chr = file_str[-1]
print(last_chr)
通过“r”而不是“rb”读取文件很重要
我注意到最后一个字符的字节值始终为 255，即使 ASCII 值的范围是从 0 到 127。当我编写一个小程序来区分 ASCII 和二进制文件时，我一开始发现这很麻烦，但这可能是一个更轻松地从硬盘恢复数据的约定。
我能想到的最简单的事情：
s="".join(list(open(rfile_directory)))
pos=s[-1:]
步骤：
现在，如果需要 int 形式的字符，只需：
pos=int(s[-1:])