4.2.1. QStringList and iteration

4.2.1. `QStringList` and iteration
	4.2. Iterators

4.2.1. `QStringList` and iteration

[ fromfile: iterators.xml id: qstringlist ]

For text processing, it is useful to work with lists of strings. A QStringList is actually a QList<QString> so you can make use of the QList public interface.^[37] In addition, QStringList has some string-specific convenience functions such as indexOf(), join(), and replaceInStrings().

Converting between lists and individual strings is quite easy with Perl-like split() and join() functions. Example 4.1 demonstrates lists, iterations, split() and join().

Example 4.1. src/containers/lists/lists-examples.cpp

#include <QStringList>
#include <QDebug>

/* Some simple examples using QStringList, split and join */

int main() {

    QString winter = "December, January, February";
    QString spring = "March, April, May";
    QString summer = "June, July, August";
    QString fall = "September, October, November";

    QStringList list;
    list << winter;                            
    list += spring;                            
    list.append(summer);                       
    list << fall;

    qDebug() << "The Spring months are: " << list[1] ;


    QString allmonths = list.join(", ");       
    qDebug() << allmonths;

    QStringList list2 = allmonths.split(", "); 

    Q_ASSERT(list2.size() == 12);              

    foreach (const QString &str, list) {       
        qDebug() << QString(" [%1] ").arg(str);
    }

    for (QStringList::iterator it = list.begin();
         it != list.end(); ++it) {             
        QString current = *it;                 
        qDebug() << "[[" << current << "]]";
    }

    QListIterator<QString> itr (list2);        
    while (itr.hasNext()) {                    
        QString current = itr.next();
        qDebug() << "{" <<  current << "}";
    }
    return 0;
}

	Append operator 1.
	Append operator 2.
	Append member function.
	From list to string - join with a ", " delimiter.
	Split is the opposite of join. Each month will have its own element.
	Q_ASSERTions abort the program if the condition is not satisfied.
	Qt foreach loop - similar to Perl/Python and Java 1.5 style for loops.
	C++ STL-style iteration.
	Pointer-style dereference.
	Java 1.2 style Iterator.
	Java Iterators point between elements.

Following is the output of Example 4.1:

src/containers/lists> ./lists
The Spring months are:  "March, April, May"
"December, January, February, March, April, May, June, July, August, September, October, November"
" [December, January, February] "
" [March, April, May] "
" [June, July, August] "
" [September, October, November] "
[[ "December, January, February" ]]
[[ "March, April, May" ]]
[[ "June, July, August" ]]
[[ "September, October, November" ]]
{ "December" }
{ "January" }
{ "February" }
{ "March" }
{ "April" }
{ "May" }
{ "June" }
{ "July" }
{ "August" }
{ "September" }
{ "October" }
{ "November" }
/src/containers/lists>

Qt tries to accommodate programmers who have various habits and styles. For example, QList::Iterator is just a typedef (alias) for QList::iterator, providing two different ways to refer to the STL-style iterator class. The QListIterator and QMutableListIterator classes provide Java-style iterators that point between list elements and access particular elements with previous() and next().

^[37]In fact, QStringList is derived from QList<QString> so it inherits QList's entire public interface. We discuss derivation and inheritance in (Chapter 6).


4.2. Iterators		4.2.2. `QDir, QFileInfo, QDirIterator`