Readind textfiles

[LordQt]

Hello friends. I actually try to read textfiles.

QFile infile("C:/testfile.txt");
 
    if (!infile.open(QIODevice::ReadOnly | QIODevice::Text))
    {
        bodyEdit->append("Can´t read file!!");
        return;
    }
    while (!infile.atEnd())
    {
        bodyEdit->append(infile.readLine());
    }

QFile infile("C:/testfile.txt");

    if (!infile.open(QIODevice::ReadOnly | QIODevice::Text))
    {
        bodyEdit->append("Can´t read file!!");
        return;
    }
    while (!infile.atEnd())
    {
        bodyEdit->append(infile.readLine());
    }

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when I have a little file ( <3000-5000 lines) its ok, but when I have a textfile ( >100.000 lines) I have a problem with the performance.

Do I make a mistake or what is it??

[Valheru]

Personally I'd read the entire file into memory and do any parsing from there. You can do this using QTextStream::readBytes(). This obviously means creating a QTextStream and using it to read the QFile, which can be done as follows:

QFile("myfile.txt");
QString contents;
 
if( file.exists() ){
        if( file.open( QIODevice::ReadOnly ) ){
            QTextStream stream( &file );
            contents = stream.readAll();
        }
    }
 
    file.close();

QFile("myfile.txt");
QString contents;

if( file.exists() ){
        if( file.open( QIODevice::ReadOnly ) ){
            QTextStream stream( &file );
            contents = stream.readAll();
        }
    }

    file.close();

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This will use a lot of memory though according to the docs, but if you have GB's anyway then who cares?

[LordQt]

Ok thx a lot,

I will try it

[Lesiok]

Are You sure that problem is with reading file ? What is bodyEdit ? If You have text file with 100000 lines You must call 100000 times append method. Maybe this is a problem.

[aamer4yu]

what file you have for 100000 lines :O ??
if we assume each line consists of 50 chars, 100000*50 = 5000000 bytes ! ~~ 4GB file !
even if u read it in memory once, u might get problems,,,
better way wud be to implement some mechanism where you seek into the file and display required bytes,,, am not sure how

[wysota]

when I have a little file ( <3000-5000 lines) its ok, but when I have a textfile ( >100.000 lines) I have a problem with the performance.

QTextEdit::append is very slow. Use QTextCursor instead.

This will use a lot of memory though according to the docs, but if you have GB's anyway then who cares?

I do. This solution is far from being scalable as you have to allocate at least two times the length of your file. With big files this is unacceptable.