Как получить строку из текстового файла с библиотеками QT

Question

Я хочу получить некоторые строки из текстового файла.Я знаю, как получить всю строку текстового файла с

QTextStream Stream (GEO); 
QString text;    
 do    
{    
text = Stream.readLine();  

}
while(!text.isNull());

.

Это нормально работает, чтобы получить весь текст под текстом QString, но мне просто нужны некоторые конкретные строки из текста, схематически как:

if the text "start" appears in the Qstring text (or the QTextStream Stream) 

save the following text under QString First

until the text "end" appears

.

Может кто-нибудь сказать мне, как это сделать или, может быть, даже дать мне небольшой пример?

Answer 1

One thing you can use is to get the indexes of the "start" and "end" with indexOf() and the just use:

QString x = "start some text here end";
QString s = "start";
QString e = "end"
int start = x.indexOf(s, 0, Qt::CaseInsensitive);  // returns the first encounter of the string 
int end = x.indexOf(e, Qt::CaseInsensitive);  // returns 21

if(start != -1) // we found it
    QString y = x.mid(start + s.length(), end);

or midRef if you dont want to create a new list. You might have to handle "end" aswell, otherwise you might go from 0 to -1 which wouldnt return anything. Maybe (end > start ? end : start)

Edit: Nevermind. If end == -1 that just means that it will return everything until the end (per default the second parameter is -1). If you don't want this you can go with my example instead and use some kind of if-statement when choosing the "end"

Edit: Noticed that I missread the doc and this will def. work:

#include <QDebug>

int main(int argc, char *argv[]) {
    QString x = "start some text here end";
    QString s = "start";
    QString e = "end";
    int start = x.indexOf(s, 0, Qt::CaseInsensitive); 
    int end = x.indexOf(e, Qt::CaseInsensitive); 

    if(start != -1){ // we found it
        QString y = x.mid(start + s.length(), ((end - (start + s.length())) > -1 ? (end - (start + s.length())) : -1)); // if you dont wanna pass in a number less than -1
        or
        QString y = x.mid(start + s.length(), (end - (start + s.length()))); // should not be any issues passing in a number less than -1, still works

        qDebug() << y << (start + s.length()) << (end - (start + s.length()));
    }
}

This produces the following resoults. The last two numbers are where "start" ends and "end" begins.

x = "start some text here end" => " some text here " 5 16

x = " some text here end" => no outprint

x = "testing start start some text here end" => " start some text here " 13 22

x = "testing start start some text here" => " start some text here" 13 -14

Or you can do it by using regEx. Wrote a very simple snippet here for you:

#include <QDebug>
#include <QRegExp>

int main(int argc, char *argv[]) {
    QRegExp rxlen("(start)(.*(?=$|end))");
    rxlen.setMinimal(true); // it's lazy which means that if it finds "end" it stops and not trying to find "$" which is the end of the string 
    int pos = rxlen.indexIn("test start testing some text start here fdsfdsfdsend test ");

    if (pos > -1) { // if the string matched, which means that "start" will be in it, followed by a string 
        qDebug() <<  rxlen.cap(2); // " testing some text start here fdsfdsfds" 
    }
}

This works even if you done have "end" in the end, then it just parse to the end of the line. Enjoy!