4.2.2. QDir, QFileInfo, QDirIterator

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

4.2.2. `QDir, QFileInfo, QDirIterator`

[ fromfile: iterators.xml id: qdiriterator ]

A directory, sometimes called a folder, is a container for files.
Because a directory can also contain other directories, it has a natural tree structure.
A directory can also contain symbolic links (called symlinks) which point to other files or directories.
A symlink is a reference that can be used instead of the name or path for most operations that handle files or directories.

Example 4.2. src/iteration/whyiterator/recurseadddir.cpp

[ . . . . ]
void recurseAddDir(QDir d, bool recursive=true, bool symlinks=false ) {
    d.setSorting( QDir::Name );
    QDir::Filters df = QDir::Files | QDir::NoDotAndDotDot;
    if (recursive) df |= QDir::Dirs;
    if (not symlinks) df |= QDir::NoSymLinks;
    QStringList qsl = d.entryList(df, QDir::Name | QDir::DirsFirst);
    foreach (const QString &entry, qsl) {
        QFileInfo finfo(d, entry);
        if ( finfo.isDir() ) {
            QDir sd(finfo.absoluteFilePath());
            recurseAddDir(sd);
        } else {
            if (finfo.completeSuffix()=="mp3")
                addMp3File(finfo.absoluteFilePath()); 
        }
    }
}
[ . . . . ]

Nonreusable part

The application listed in Example 4.3 reuses QDirIterator to accomplish the same thing with fewer lines of code.

Example 4.3. src/iteration/diriterator/diriterator.cpp

[ . . . . ]
int main (int argc, char* argv[]) {
    QCoreApplication app(argc, argv);
    QDir dir = QDir::current();
    if (app.arguments().size() > 1) {
        dir = app.arguments()[1];
    }
    if (!dir.exists()) {
        cerr << dir.path() << " does not exist!" << endl;
        usage(); 
        return -1;
    }
    QDirIterator qdi(dir.absolutePath(),
            QStringList() << "*.mp3",
            QDir::NoSymLinks | QDir::Files,
            QDirIterator::Subdirectories );
    while (qdi.hasNext()) {
        addMp3File(qdi.next());
    }
}
[ . . . . ]

In Example 4.2, the call to the project-specific function, addMp3File() occurs inside the definition of the function, recurseAddDir(), that manages the iteration, severely limiting the reusability of that function.
In Example 4.3, QDirIterator manages the iteration.
The call to addMp3File() occurs in the client code for QDirIterator (main()) and, thus, can have no effect on the reusability of that class.


4.2.1. `QStringList` and iteration		4.3. Relationships