ASCII Number to Strings & Chars

[ttimt]

I search for help online for a whole day, maybe 2.
I outputted strings to its ascii value to a file by using the for loops and char .at()

all these output went well, but how can i read it back from the file?

i tried qt library and native c++ (not problem in codeblocks, but i want to have gui)

I'm not sure how to use char array below because I wont know how long the string is, how many chars are there.
And in my file, its not only 1 line of code. For example, when i input

ABCD
AAAA
BBBB

my file will become

65 66 67 68
65 65 65 65
66 66 66 66

ifstream myFile("abc.txt");
 
        while(myFile >> a >> a1 >> a2){
 
 
             a = a - 1;
             a = a1 - 1;
             a= a2 - 1;
             QString abc = QChar( a + a1 + a2);
             ui->aLine->setText(abc);
}

ifstream myFile("abc.txt");

        while(myFile >> a >> a1 >> a2){

                
             a = a - 1;
             a = a1 - 1;
             a= a2 - 1;
             QString abc = QChar( a + a1 + a2);
             ui->aLine->setText(abc);
}

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when i use just these codes below, it will only shows the first character of the whole strings.
And is there a way to make the abc still usable outside the loop? cause i need to set it after the loops right? and it always shows not declared.

myFile >> a
             QString abc = QChar( a );
             ui->aLine->setText(abc);

myFile >> a
             QString abc = QChar( a );
             ui->aLine->setText(abc);

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QFile mFile("abc.txt");
    mFile.open(QIODevice::ReadOnly | QIODevice::Text);
    QDataStream in(&mFile);
 
in >> a; // Not sure what's next. it keeps error

QFile mFile("abc.txt");
    mFile.open(QIODevice::ReadOnly | QIODevice::Text);
    QDataStream in(&mFile);

in >> a; // Not sure what's next. it keeps error

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