How to use QFile, QByteArray and QString?

[jsulm]

@victor-wang Again: what is "last word"? How is it defined? I still don't understand what information you want to get. Are those MAC2, Model, PN, ...?

[victor wang]

@jsulm

For example the picture i gave you.
The last word means the last line of the "6".
Picture here

Those words is what i write in eeprom.
For other example if i write "skdjb,smdnv6546321" into eeprom.
Then the last Alphabet is "1" and i just want to read what i write.

[jsulm]

@victor-wang Then read line by line and parse each line to check whether it is what you want.
And you should use correct wording, else it's hard to understand what you mean: a word is not a line.

[victor wang]

@jsulm
Sorry, how to parse it?
I will not know what will other people write, how can parse?

[jsulm]

@victor-wang OK, you don't know what others are writing, right? But you know what you want to read, right?
If so then:

QByteArray whatIWantToRead = "ABCD";
QString line = file.readLine();
if (line == whatIWantToRead)
    // do something

[victor wang]

@jsulm
If i want to read a~z、A~Z and some other exclamation mark and question mark and etc..
I have to write all of it into whatIWantToRead ?

[jsulm]

@victor-wang You can use regular expressions, see https://en.wikipedia.org/wiki/Regular_expression and http://doc.qt.io/qt-5.8/qregularexpression.html

[victor wang]

@jsulm
Do you have an example?
Or can i parse it by ASCII ?

[jsulm]

@victor-wang There are a lot of examples for regular expressions on the Internet

[J.Hilk]

@victor-wang

If you know, that valid lines always contain legit chars between 'A' and 'z'

You can make a simple If-statement with the first char in your bytearray:

QByteArray bArray = file.readline();
if(bArray[0] < QLatin1Char('A') || bArray[0] > QLatin1Char('z'))
     //Abort condition met

use QLatin1Char if its ASCII, QChar if its unicode.