How to use QDir(); to get a path " with native separators"

JonB

@ademmler said in How to use QDir(); to get a path " with native separators":

Because launching an external command does not work as you described!

Yes it does. Maybe your code is incorrect?

The fact remains that MacOs/LInux should be just as happy with passing "/Users/ademmler/test me/some.file" as with /Users/ademmler/test\ me/some.file.

I and loads of people happily use toNativeSeparators() for paths with spaces to pass to QProcess across platforms.

KroMignon

@ademmler said in How to use QDir(); to get a path " with native separators":

Because launching an external command does not work as you described!

I have used QProcess to launch external application on Linux, Windows and Android system and it always works.
I never had issues with spaces or path separator.

I think the issue is in the way to use QProcess.
If you want help, you have to show the code which is not working, not basic usage of QDir.

Cobra91151

Hello!

You can use the QDir::separator() (https://doc.qt.io/qt-5/qdir.html#separator) or QDir::toNativeSeparators() (https://doc.qt.io/qt-5/qdir.html#toNativeSeparators) methods. It will return: "/" under Unix and "\" under Windows.

Also, you can try to replace "/" with "\" and it will work, for example: qDebug() << "Path: " << mydir.currentPath().replace("/", "\\") << Qt::endl;

Happy coding!

ademmler

@Cobra91151 In another post I have made before - it got told "never" to use QDir::Separator();

I wrote this minimal app to learn and understand how QDir really works.

@KroMignon I split my question into multiple posts, because they always belong to different problems and questions. Also I create in most cases a bare bone (minmal) app for testing.
I thought it is the recommended practice.

You find the issue about "launching a command" here:
https://forum.qt.io/topic/118236/qprocess-how-to-debug-the-full-command-send-used-to-start-the-process

Christian Ehrlicher

@ademmler said in How to use QDir(); to get a path " with native separators":

it got told "never" to use QDir::Separator();

You should never use it inside Qt but since you're calling an external program which expects the correct separators you must use it.

ademmler

@Christian-Ehrlicher said in How to use QDir(); to get a path " with native separators":

QDir::Separator();

ok - I understood - I will have a look at it agin.

A) Assume I have a folder in "/Users/ademmler/Desktop/myapplication/test me"

I start with: QDir mydir = QDir(QCoreApplication::applicationDirPath());
If I do mydir.cd("test me"); I would expect

mydir.toNativeSeparators(mydir.currentPath()) ? to give me
"/Users/ademmler/Desktop/myapplication/test me/"

Instead it shows "/Users/ademmler" only, which is the root where the application folder lays.

What I am doing wrong here?

And on top I was told that Process will deal with the correct path and separators automatically.
is this true or doe I need to prepare my arguments using "QDir::Separator(); ?

ademmler

This post is deleted!

Christian Ehrlicher

@ademmler said in How to use QDir(); to get a path " with native separators":

And on top I was told that Process will deal with the correct path and separators automatically.

This is wrong for the arguments you pass to the process - Qt will not modify them in any way.

QDir mydir = QDir(QCoreApplication::applicationDirPath());

Please take a look what mydir contains after this call. I would guess it's not. Then QDir::chdir() returns a bool which you should also check and at least QDir::toNativeSeparators() is a static function and needs no object. And it simply does a QString::replace('/', "\") on windows and QString::replace("\", '/') on linux so it can't be the reason for the wrong directory at all.

ademmler

@Christian-Ehrlicher said in How to use QDir(); to get a path " with native separators":

This is wrong for the arguments you pass to the process - Qt will not modify them in any way.

Very good to know - thx.

Cobra91151

@Christian-Ehrlicher said in How to use QDir(); to get a path " with native separators":

@ademmler said in How to use QDir(); to get a path " with native separators":

it got told "never" to use QDir::Separator();

You should never use it inside Qt but since you're calling an external program which expects the correct separators you must use it.

Hello! I am curious, why not to use QDir::separator() inside Qt? I am using this method quite a bit in my apps on Windows and it works well. Thanks.

JonB

@Cobra91151
It depends where/why you use it. I think the docs is pretty clear:

Returns the native directory separator: "/" under Unix and "\" under Windows.

You do not need to use this function to build file paths. If you always use "/", Qt will translate your paths to conform to the underlying operating system. If you want to display paths to the user using their operating system's separator use toNativeSeparators().

While you manipulate paths within Qt you would be best using /, regardless of platform. So you don't need this. Only when you come to, say, passing a Qt-style path to an operating system command or displaying a message do you need to use QDir::separator() or toNativeSeparators().

I happenstanced across https://agateau.com/2015/qdir-separator-considered-harmful/, that is short, clear (big writing, friendly font ;-) ) and illustrates the trap.

ademmler

@Cobra91151

Because a day - here in the forum - i got this informations:
"Qt use "/" as path separator for all OS.
QDir::separator will only be used in QDir::toNativeSeparators."

"While you are using Qt path functions you should always use /, and that is what they will return to you. If you want the native separators QDir has to/fromNativeSeparartors(), but these should only be used if passing to something external, like an OS command."

Hence for me it meant - never use "QDir::separator" it is Qt internal only ....

What I know get is better to use something like this example:

QString mypath =  QStandardPaths::writableLocation(QStandardPaths::DesktopLocation) + QDir::separator() + "my folder";

Thank you very much for making it more clear.

ademmler

@Christian-Ehrlicher said

This is wrong for the arguments you pass to the process - Qt will not modify them in any way.

But it will add "spaces" between all argument "peaces".

Wich leads into this to be correct:
arguments << "-opiton1" << "-ringthebell" << "yes" ... ;

JonB

@ademmler said in How to use QDir(); to get a path " with native separators":

QString mypath = QStandardPaths::writableLocation(QStandardPaths::DesktopLocation) + QDir::separator() + "my folder";

For anyone coming across this: As per the article referenced earlier, this is precisely the wrong place to use QDir::separator().

ademmler

@JonB thx for responding.
Maybe I am mistaken - but from the discussion above I got the recommendations to use QDir::separator(). Now I am not sure which answer is the correct one.

Pls see above first comment from @Christian-Ehrlicher

Cobra91151

@JonB @ademmler

I have checked it on Windows, this path will work C:/test/path\test.exe even thought it is wrong. So, this code QString myPath = QStandardPaths::writableLocation(QStandardPaths::DesktopLocation) + QDir::separator() + "my folder"; in your case:

QStandardPaths::writableLocation(QStandardPaths::DesktopLocation) will have "/" and
QDir::separator() + "my folder" will have "\my folder".

It will work, but the path is not correct. Instead, there are a lot of options we can do here.
QString myPath = QStandardPaths::writableLocation(QStandardPaths::DesktopLocation).replace("/", "\\") + "\\" + "my folder";
QString myPath = QStandardPaths::writableLocation(QStandardPaths::DesktopLocation).replace("/", "\\") + "\\my folder";

Or

QString myPath = QDir::toNativeSeparators(QStandardPaths::writableLocation(QStandardPaths::DesktopLocation).append("/") + "my folder");

QString myPath = QDir::toNativeSeparators(QStandardPaths::writableLocation(QStandardPaths::DesktopLocation).append("\\") + "my folder");

QString myPath = QDir::toNativeSeparators(QStandardPaths::writableLocation(QStandardPaths::DesktopLocation) + "/" + "my folder");

QString myPath = QDir::toNativeSeparators(QStandardPaths::writableLocation(QStandardPaths::DesktopLocation) + "\\" + "my folder");

QString myPath = QDir::toNativeSeparators(QStandardPaths::writableLocation(QStandardPaths::DesktopLocation) + QDir::separator() + "my folder");

The path should contain all "/" or "\" to be correct.
All, these paths will return: "C:\\Users\\username\\Desktop\\my folder" and it is valid and correct for Windows, so you can use it to build paths and display to the user. The QDir::toNativeSeparators() method will display the correct "/" or "\" depending on the current OS, and will fix the path issue with QDir::separator().

JonB

@Cobra91151
That's a long answer! :)

Yes, the issue will show up under Windows only. C:/test/path\test.exe is the kind of thing that will result from using QDir::separator(). Which looks wrong, and may (or may not) cause problems.

The point is to just use / while passing a path around in Qt code. So

QString mypath = QStandardPaths::writableLocation(QStandardPaths::DesktopLocation) + "/my folder";

would be best.

You only need QDir::separator() or toNativeSeparators() when you're e.g. passing to OS or printing.

JKSH

@ademmler said in How to use QDir(); to get a path " with native separators":

Maybe I am mistaken - but from the discussion above I got the recommendations to use QDir::separator(). Now I am not sure which answer is the correct one.

Pls see above first comment from @Christian-Ehrlicher

@Christian-Ehrlicher only said that you should use native separators when writing the path to an external non-Qt process.

In your example, you are not writing the path to an external process. You are building up a path inside Qt. So, QDir::separator() is not appropriate here.

The correct way to build your path in a cross-platform way is QString mypath = QStandardPaths::writableLocation(QStandardPaths::DesktopLocation) + "/my folder"; like @JonB said.

ademmler

@Christian-Ehrlicher @Cobra91151 @JonB @KroMignon and all the others:

This had been a very longish task - but I am glad about it - because it demystified some obstacles for me.
Somehow QProcess(); and QStandardPaths(); got mixed up - but that was very good for some reason.

Thx again - which answer shall I mark as the solution now? You ALL have been very helpful.

Another question came up into my mind. Whats about using QFile::copy(); function.
Does this take care of platform depended details (in path names) automatically ?

QString targetFile(myFolder.absolutePath() + "/" + base + "." + ext);
QFile sourceFile(inputFile);
bool    ok = sourceFile.copy(targetFile);

aha_1980

Hi @ademmler,

Another question came up into my mind. Whats about using QFile::copy(); function.
Does this take care of platform depended details (in path names) automatically ?

Every Qt API takes forward slashes as separator. You only need native separators when you display a path to the user or when you pass it to some thirdparty API. (Side node: even the Windows API allows forward slashes in many cases).

So yes, QFile::copy takes care for the platform details itself.

Regards