Get file name, line number and function name in QML Javascript. How?

[bogong]

Hello all!
Is there any way to get file name, line number and function name in QML Javascript without using QDebug? The key point WITHOUT QDebug. I know how to get it in C++ via FILE, LINE, FUNCTION. I am seeking something like this C++ function but for QML/JavaScript.

[J.Hilk]

@bogong
I'm not entirely sure, and I would love, if someone has more insight here.

What I do is using console.log() and print information that way for example:

function myFunction() {
     console.log("myFunction", this.toString(), this, objectName)
}

[JonB]

@bogong
I know nothing about QML. In JS it's not native, have a look at these "tricks" and see if they work for you/are suitable:

• https://stackoverflow.com/a/47105238/489865
• https://stackoverflow.com/questions/50877998/how-to-get-filename-and-line-number-in-javascript-dynamically

[raven-worx]

@JonB
i can confirm that parsing new Error().stack works also in QML, already used it myself
Simply parse for \n, @ and : to get the info you want.

[bogong]

@raven-worx Got it. Thx.

[bogong]

Issue solved.

var err = new Error();
console.log(inMessage,err.stack);

[KH-219Design]

This stack tactic from @raven-worx looks very useful. I'm glad to have learned it just now.

I'll come at this from a different angle, in case anyone was unaware of qSetMessagePattern.

I have been using QML and logging with console.log, and I see the QML file name and line number attached to every output statement.

In my main function, I invoke qSetMessagePattern, being sure to make "%{file}(%{line}):" part of the specified pattern:

• https://github.com/219-design/qt-qml-project-template-with-ci/blob/441e072d50613bf/src/app/main.cc#L25

Then a simple call to console.log such as:

• console.log(fAwesomeFamily)
• used here: https://github.com/219-design/qt-qml-project-template-with-ci/blob/master/src/libstyles/imports/libstyles/Fonts.qml#L11

Produces the following level of detail when Qt prints it to stderr:

2021-01-03 18:58:56 [QT-debug][v-441e072d50][thr:18325]qml: qrc:/libstyles/Fonts.qml(15): Font Awesome 5 Free

For QML code, this works in both debug and release builds.

That stands in contrast to Qt logging (with ""%{file}(%{line}):"") in C++ code. My C++ Qt logging shows up as desired in a debug build, looking like "event_filter.cc(74):". But in release builds it shows "unknown(0):". However, with QML logging I see the filename and line of the QML source no matter whether the build was debug or release.

[ondrejandrej]

@KH-219Design said in Get file name, line number and function name in QML Javascript. How?:

qSetMessagePattern

Thank you for this great tip!

BTW the file name is printed with the whole path, which is taking a lot of space. Is there a way to print file name only?

[KH-219Design]

@ondrejandrej said in Get file name, line number and function name in QML Javascript. How?:

Is there a way to print file name only?

Yes and no.

These are the tokens accepted by qSetMessagePattern: https://doc.qt.io/qt-5/qtglobal.html#qSetMessagePattern

For filename, there is only one choice (the "%{file}" that we have already seen). There isn't anything like "shortfile" or "filebasename" from what I can see.

So I can think of two options.

(1) you can write your own QtMessageHandler function, as done in this example: https://github.com/qt/qtbase/blob/fcea8e7aa8a/examples/vulkan/hellovulkanwidget/main.cpp#L79

Anything that is logged will get routed to your handler function, and you can get the filename and all the other info from the QMessageLogContext passed to the handler, and you can then have total control over logging.

(2) Keep the logging as you have it now (with long file name and file path), and write a separate little bash script (or perl script, or python script) to filter the output whenever you pipe logging info to your script.

I guess (2) might not be great if you are looking at the output inside a debugger.

Nonetheless, here is an example of what I mean in (2), as demonstrated at a bash prompt...

If I launch my app like so:

./app

This long line of output appears

2021-04-26 08:33:52 [QT-info][thr:1991]/opt/repositories/client/self/heory/gits/heory/src/app/event_filter.cc(76): this GUI thread is running unblocked. 

But if I launch it and pipe output through a sed filter:

./app |& sed 's/opt\/repositories\/client\/self\/heory\/gits//'

That same log line will shrink to:

2021-04-26 08:33:46 [QT-info][thr:1951]//heory/src/app/event_filter.cc(76): this GUI thread is running unblocked.

(Sidenote: in case the |& that I like to call pipepersand is as new to anyone as it is recently new to me, here is a reference on piping in bash with {pipe,ampersand})