remove line from Qstring - qt

Question

I have a QString with 5 lines
"AAAAAR"
"BBBBB"
"CCCRC"
"DDDDD"
"EEEEE"
I would like to search 'R' character only with lines from 2 to 4 If one of them contents 'R' then remove the line from my QString
I tried many method but without successs.

Answer 1

You can split the string for each line, giving you a QStringList with 5 strings in it. Then iterate from 2 to 4 and if the string contains R, remove the string from the string list, and in the end, join the string list back again.
QString s("AAAAAR\nBBBBB\nCCCRC\nDDDDD\nEEEEE");
QStringList l = s.split('\n');
int i = 1, stop = 4;
while (i < stop) {
if (!l[i].contains('R')) ++i;
else {
l.removeAt(i);
--stop;
}
}
s = l.join('\n');
This solution should be more flexible and work regardless of the input, just select the range you want the check in.
Ironically enough, if the loop is iterated in reverse there is no problem with leaving holes and keeping track of the total count.
for (int i = 3; i > 0; --i) if (l[i].contains('R')) l.removeAt(i);

Answer 2

Similar to ddriver's solution but using iterators
#include <QApplication>
#include <QString>
#include <QStringList>
#include <QtCore>
int main(int argc, char** argv)
{
QApplication app(argc,argv);
QString s("AAAAAR\nBBBBB\nCCCRC\nDDDDD\nEEEEE");
QStringList l = s.split('\n');
for( QStringList::iterator it = ++l.begin(); it != --l.end(); ) {
if( it->contains('R') ) {
it = l.erase(it);
} else {
++it;
}
}
s = l.join("\n");
qDebug() << l;
return app.exec();
}
Output:
("AAAAAR", "BBBBB", "DDDDD", "EEEEE")
I don't use in increment in the for loop but instead use
QList::erase(iterator pos) which Removes the item associated with the iterator pos from the list, and returns an iterator to the next item in the list.
I assume more generically that you want to loop from the 2nd to the second to last element, irrespective of the number of elements.
EDIT: in case you want to move a specific element in the container you could e.g. use std::advance
#include <QApplication>
#include <QString>
#include <QStringList>
#include <QtCore>
#include <iterator>
int main(int argc, char** argv)
{
QApplication app(argc,argv);
QString s("AAAAAR\nBBBBB\nCCCRC\nDDDDD\nEEEEE");
QStringList l = s.split('\n');
QStringList::iterator it = l.begin();
QStringList::iterator itEnd = l.begin();
std::advance(it,2); // set the number to whatever start position you want
std::advance(itEnd,4); // set the number to whatever end position you want
for( ; it != itEnd ; ) {
if( it->contains('R') ) {
it = l.erase(it);
} else {
++it;
}
}
s = l.join("\n");
return app.exec();
}