Reading a text file in Qt

Question

I want to read a huge text file in which I will divide the lines according to a comma (,) and store the lines in an array. So how to do it. Is there any class that performs an action like StringTokenizer, as in badaOS. I tried QFile but could not read the whole file.

Answer 1

QTextStream allows you to read line by line

QFile file(hugeFile);
QStringList strings;
if (file.open(QIODevice::ReadOnly | QIODevice::Text))
{
    QTextStream in(&file);
    while (!in.atEnd()) {
        strings += in.readLine().split(";"); 
    }
}

Answer 2

You can use file streams.

QFile file = new QFile(hugeFile);      
file.open(QIODevice.OpenModeFlag.ReadOnly);       
QDataStream inputStream = new QDataStream(file);
QStringList array;
QString temp;

while(!inputStream.atEnd()) {
  inputStream >> temp;
  array << temp.split(";");
}

Please note that this is unverified (pseudo) code, hope this helps.

Answer 3

:

QFile file( ... );
file.read(1000); // reads no more than 1000 bytes

:

file.readLine();

, .

Answer 4

, file.read(an_appro_number), file.atEnd() - false.

( File.read()), "(, QString ( )). ',', ( QString split(): X- ( 1000 1 ) , . ( file.atEnd()) . , . , file.atEnd():)

Or, as an alternative, you can read the file character by character and check the "" manually, but it is always better to read more than 1 character (this is more efficient if you read more).

Answer 5

It will not capture spaces after the decimal point. If this is unacceptable, feel free to optimize the regex. You can probably also reduce the number of inclusions at the top. I was just happy. I tested this in a file with a line of 1600, and it seems to have worked well with Qt 5.6

#include <QCoreApplication>
#include <QFile>
#include <QIODevice>
#include <QRegularExpression>
#include <QRegularExpressionMatch>
#include <QRegularExpressionMatchIterator>
#include <QString>
#include <QStringList>
#include <QTextStream>

int main(int argc, char * argv[])
{
    QCoreApplication app(argc, argv);

    QFile file("C:\\PathToFile\\bigFile.fileExt");
    QStringList lines;
    QStringList matches;
    QString match;

    file.open(QIODevice::ReadOnly | QIODevice::Text);
    while(!file.atEnd())
    {
      lines << file.readLine();
    }
    file.close();

    QRegularExpression regex("(^|\\s|,)\\K\\w.*?(?=(,|$))");
    QRegularExpressionMatchIterator it;

    foreach (QString element, lines)
    {
        it = regex.globalMatch(element);

        while(it.hasNext())
        {
            QRegularExpressionMatch qre_match = it.next();
            match = qre_match.captured(0);
            matches << match;
        }
    }

    return 0;
}