Using variables ending with numbers



  • Hi,

    I deal with a bunch of variables named:
    nom1, nom2, nom3, nom4,.....
    I would like to call the variable (nomX).
    I tried :
    @
    ("nom%1).arg(X)="Sam";
    (QString("nom%1).arg(X))="Sam";
    @
    but with no success.

    Could you tell me how to do it.
    Thank you


  • Moderators

    According to the docs of Qt5 it would more like:
    @
    QString str;
    str = "nom%1";

    str.arg("", "X");
    @

    [edit, running into an issue with the editor here.
    the first argument of str.arg shall be "% 1 f" without spaces. ]

    However, I am not sure it looks stupid and might be wrong in the docs. I do not use QString very often, more the std::string variant.

    But this should work:
    @
    QString str;
    str = "nom";
    QString str2 = str + QString ("X");
    @
    or
    @
    QString str;
    str = "nom";
    QString str2 = str + "X";
    @



  • Hi,
    Thank you for your reply.
    My request was not clear. Let me put it that way:

    @
    in header
    QString nom1;
    QString nom2;
    @
    @
    in .cpp
    nom1="Sam"
    nom2"Pierre";

    QString st="nom";
    QString st2=st+"1";
    st2="Paul";
    // nom1 should now be : Paul - but it isn't , only st2="Paul"
    @



  • @QStringList nom;
    nom.append("Sam");
    nom.append("Pierre");

    QString someOtherString = nom.at(0); // will be "Sam"@

    This isn't a scripting language, so building variable identifiers from strings is rightly discouraged, for performance, security and anti-spaghetti-code reasons. Through hackery (a.k.a. meta object system), it is possible though. But don't do it. Leads to bad programs, and we've got plenty of those.


  • Moderators

    As already explained by DerManu.

    Or you may use "QMap":http://qt-project.org/doc/qt-5.0/qtcore/qmap.html .
    @
    QMap<QString, QString> myMap;
    myMap["nom1"]="Sam";
    myMap["nom2"]="Pierre";
    myMap["nom3"]="Paul";

    QString st = "nom";
    QString st2 = st + "1";

    qDebug() << myMap[st2];
    @
    should work.



  • @koahnig, I slightly disagree with the QMap usage here. Because that number in the end of "nom" just screams for an integer index based container like QVector or QList (@phil: QStringList is just QList<QString>), and so one should use them, and not the more key-generic QMap<QString, QString>. If non-continuous index ranges are needed, QMap<int, QString> would be okay.


  • Moderators

    [quote author="DerManu" date="1371374572"]@koahnig, I slightly disagree with the QMap usage here. Because that number in the end of "nom" just screams for an integer index based container like QVector or QList (@phil: QStringList is just QList<QString>), and so one should use them, and not the more key-generic QMap<QString, QString>. If non-continuous index ranges are needed, QMap<int, QString> would be okay.[/quote]
    Yes, you are right, but the question is what is the real case at the end. If it is a simplified example and the names will be a bit more complex and not just a number appended, it might make sense.



  • Thank you to both of you


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