Qt Creator: log(message) doesn't print any output

Robert Hairgrove

According to the docs at https://doc.qt.io/qt-6/qmake-test-function-reference.html#log-message, Qt Creator/QMake has a log(message) function in addition to the message(message) function.

However, when qmake runs, nothing is written to the "General Messages" pane. I am using Qt Creator 17.0.1 on Linux Ubuntu 24.04 with Qt 6.9.2.

Where does the output of log() get written?

Robert Hairgrove

OK, I found it. log() is written to Compile output.

Robert Hairgrove

Now that I have found the output, I am having trouble formatting it. According to the docs, which I read carefully, it says:

Unlike the message function, neither prepends text nor appends a line break...

So I dutifully insert the line feeds myself as "\n" in the text. However, instead of writing an actual line feed to the output, I get the "\n" as literal tokens! When I escape the line feed token as "\\n", I get "\n\n". But no actual line feed.

I could use the message() function, but as the docs say, this prepends Project MESSAGE: to every single line of output, which is why I wanted to use log() in the first place.

So the question is, how to get nicely-formatted output from log()?

Robert Hairgrove

Solved this by the following:
Define a variable close to the top of your *.pro file which stores the result of $$escape_expand(\\n), e.g.:

NL = $$escape_expand(\\n)

When you want to use log("some string"), with a newline at the end, write it like this:

log("some string$${NL}")

Quirky, but it works.

Apparently, the log() function is a thin wrapper around the C runtime fputs() function (which I found by looking in the source code for qmake in the file Qt/<version>/Src/qtbase/qmake/library/qmakebuiltins.cpp).

SGaist

@Robert-Hairgrove this brought back some memories ! I don't remember exactly why I needed that but that trick was very good to know.
I think I needed to build a set of commands to be execute or something like that.