Finding exact match for QString in a QStringList

Vinod Kuntoji

I have stringlist,

[marking_property,property,prop,props]

Here, I want to replace, property with ID,
I expect, the stringlist should be

[marking_property,ID,prop,props]
How do I do this using QRegularExpression?

aha_1980

Hi, have you tried http://doc.qt.io/qt-5/qstringlist.html#replaceInStrings-2 ? It contains a small example and seems to do exactly what you want.

Vinod Kuntoji

@aha_1980 ,

QString s = "Some text MyWord some more text MyWordAgain"
s.replace("MyWord","AnotherWord")
Now I want to replace occurrences of 'MyWord' only and 'MyWordAgain' would not be replaced.

jsulm

@Vinod-Kuntoji You can use a regular expression with http://doc.qt.io/qt-5/qstring.html#replace-12

Vinod Kuntoji

@jsulm ,

I tried like this,

    QFile data(filename);
    data.open(QIODevice::Text | QIODevice::ReadOnly);
    QString dataText = data.readAll();

    QRegularExpression re(oldTag);
    QString replacementText(newTag);
    if(!dataText.contains(re)){
        qDebug() << "String Not Found.." << endl;
        return;
    }
    dataText.replace(re, replacementText);
    QFile newData(filename);
    if(newData.open(QFile::WriteOnly | QFile::Truncate)) {
        QTextStream out(&newData);
        out << dataText;
    }
    newData.close();

But it is not replacing the exact string.

jsulm

@Vinod-Kuntoji Well, if you only want to replace whole words then you need something like this as regular expression: "\s+MyWord\s+" you cannot just use MyWord as regular expression and expect it to only replace whole words.
You can use this to test regular expressions: https://regex101.com/

JonB

@jsulm
The problem with \s+MyWord\s+ is that it requires whitespace on either side, so for example if the complete string is only MyWord it won't match.

Most regular expressions syntaxes these days allow \bMyWord\b where \b is a non-eat-character "word-boundary" match. I think Qt is saying it allows Perl-flavor regexps, and that supports \b (and \B).

jsulm

@JNBarchan It was just an example. The exact expression depends on exact needs.