Question

I see Qt has a nifty class name QUrlInfo. It has methods/functions that I’d like to use but I’m confused about how to use this class. The initialization seems very strange and awkward.
http://doc.qt.io/qt-4.8/qurlinfo.html#setLastModified

For example:

I’d like to use its method named QUrlInfo::setLastModified so that I can set the lastModified timestamp for a local file. (also on a shared netw file but right now I just want to focus on a local file).

Let’s say that the local file is “D:/dir1/dir2/file.txt”.

How can I use QUrlInfo when I only have the fullFileName (“D:/dir1/dir2/file.txt”) of an item and wish to use QUrlInfo’s GET and SET methods? In particular I’d like an example of how I can create a QUrlInfo object and use its QUrlInfo::setLastModified method.

Deeper explanation:

My main source of confusion comes from the fact that its constructor looks like the
following

//Version 1: Problem is you must already have a QUrlInfo object.
QUrlInfo ( const QUrlInfo & ui )

//Version2: Problem is you must already know everything about the file.
//This makes QUrlInfo objects large set of GET methods useless for the most part
//since you must already know all the GET info prior to making a QUrlInfo object.
//Chicken and egg scenario.  I don't see what is point of making a class that gets
//info... but... you must already know all that info to begin with or you can't
// initialize the the class.  
QUrlInfo ( const QString & name, int permissions, const QString & owner, 
const QString & group, qint64 size, const QDateTime & lastModified, 
const QDateTime & lastRead, bool isDir, bool isFile, bool isSymLink, 
bool isWritable, bool isReadable, bool isExecutable )

//Version3: Same problem as in version 2.
QUrlInfo ( const QUrl & url, int permissions, const QString & owner, 
const QString & group, qint64 size, const QDateTime & lastModified, 
const QDateTime & lastRead, bool isDir, bool isFile, bool isSymLink, 
bool isWritable, bool isReadable, bool isExecutable )

Answer 1

From the docs..

Note that setting values does not affect the underlying resource that the QUrlInfo provides information about; for example if you call setWritable(true) on a read-only resource the only thing changed is the QUrlInfo object, not the resource.

This class is only meant for managing information that you already know about a resource.

There are some attributes that can be set using QFile but these are limited and come with warnings in the docs as the behavior is OS dependent. You will likely need to use native APIs to manipulate file attributes reliably.