Split a QString and remove the rest

Volebab

I want to split a QString using a delimiter and get the text after, removing everything that comes after that text, for example.

QString a = "@john.foo";
QString b = "@john_foo";
QString c = "@john foo";
QString d = "@john!foo";

auto result = a.split('@').last();

I want the result to be only john in all cases above. I want to remove everything that comes after, if it's a space or any other character that is not alphabetic or numeric.

Paul Colby

Just checking, what would you expect from:

QString e = "mary@jane@john@peter_russell";

jane? or peter?

Volebab

@Paul-Colby - Always the last one, and about the "_", it would be valid, we can see it as a replacement for a space.

JohanSolo

You could use a QRegExp (Qt 4.8) or a (QRegularExpression (Qt 5.x))[http://doc.qt.io/qt-5/qregularexpression.html], this would allow you to capture any alphanumeric character following @.

Paul Colby

@Volebab said:

@Paul-Colby - Always the last one, and about the "_", it would be valid, we can see it as a replacement for a space.

I take that to mean "peter".

As @JohanSolo said, you can use QRegularExpression - that would probably be easiest, but not necessarily fastest (depends on which is more important to you).

For example:

QString one(const QString &input)
{
    const QRegularExpression re(".*@([A-Za-z0-9]+)");
    const QRegularExpressionMatch match = re.match(input);
    return match.hasMatch() ? match.captured(1) : QString();
}

...
    QString a = "@john.foo";
    QString b = "@john_foo";
    QString c = "@john foo";
    QString d = "@john!foo";
    QString e = "mary@jane@john@peter_russell";

    qDebug() << "a" << one(a);
    qDebug() << "b" << one(b);
    qDebug() << "c" << one(c);
    qDebug() << "d" << one(d);
    qDebug() << "e" << one(e);

Outputs:

a "john"
b "john"
c "john"
d "john"
e "peter"

Volebab

You were right, regex is the best option here. I asked because I wanted to know if there's any alternative.
Thank you guys.

Paul Colby

And a (possibly) faster version without using regular expressions:

QString two(const QString &input)
{
    const int startPos = input.lastIndexOf('@', -2) + 1;
    if (startPos <= 0) return QString(); // Failed to match.
    int endPos;
    for (endPos = startPos + 1;
         (endPos < input.size()) && (input.at(endPos).isLetterOrNumber());
         ++endPos);
    return input.mid(startPos, endPos - startPos);
}

Output is identical to the above version. There may be differences between to two, but not in the given test scenarios ;)

Cheers.