静态函数将不同类型的QList转换为QString

Question

I have a QList which contains string, int, double and date values. I want to convert the QList to a QString and return it within a QString returning function. Is there a static function I can use or what am I missing here? My current code:

QString Product::toString()
{
    QStringList listString;
    QString outString;

    for(int i =0; i < size(); i++)
    {
        listString << at(i)->toString();
    }
    outString = listString.join("\n");
    return outString;
}

Answer 1

Notes:

• I am assuming Product::at(int) is returning a Transaction , given a previous question.

• I am also assuming OP mean "built-in" when he or she wrote"static"

The for can be removed using built-in functions. Some (many?) will find the new syntax less understandable, though.

QString Product::toString()
{
    QStringList aggregate;
    std::transform(m_transactions.begin(),
                   m_transactions.end(),
                   std::back_inserter(aggregate),
                   std::bind(std::mem_fn(&Transactions::toString), std::placeholders::_1));
                   // or : [](const Transaction& transaction){ return transaction.toString(); });

    return aggregate.join("\n");
}

std::transform will transform every m_transactions elements using Transaction::toString() , and place the results into aggregate .

std::back_inserter means "use QStringList::push_bask to record the results". If QStringList had a resize(int) like QVector does, we could have used aggregate.begin() instead.

The unary function is a bit tricky, as it needs to be converted into a unary function, which what std::bind / std::mem_fn is doing. If you are using C++11, you can use a lambda instead.

---

Also from the previous question, @SingerOfTheFall's remark is valid:

I also find it a little odd to save transactions inside of products. A better design would be having a separate class that could store them.

If you keep this design, Transaction Product::at(int) and int Product::size() should be renamed to make the link with Transaction explicit, like getTransaction and getNumberOfTransactions .