QtCreator 4.1.0 Qt 5.7.0 Windows 10 MinGW problem

[JKSH]

@ad5xj said in QtCreator 4.1.0 Qt 5.7.0 Windows 10 MinGW problem:

I get this error when linking (abbr for clarity)

Do you only get errors for FFTW, or Qwt as well?

LIBS += -L$${FFTW3_LIB_PATH} -lfftw3-3.dll

That's supposed to be -lfftw3-3 (no ".dll")

LIBS += -L$${FFTW3_LIB_PATH}/libfftw3-3.dll
LIBS += -L$${FFTW3_LIB_PATH}/libfftw3l-3.dll
LIBS += -L$${FFTW3_LIB_PATH}/libfftw3f-3.dll

FFTW3_LIB_PATH == "C:/FFTW3/", right? That means your lines expand to things like LIBS += -LC:/FFTW//libfftw3-3.dll (2 slashes).

Let's do a sanity check: Replace all the variables in your *.pro file with hard-coded paths, e.g. LIBS += -L"C:/FFTW3/" -lfftw3-3 -lfftw3l-3 -lfftw3f-3 and see what happens.

[EDIT: @kshegunov beat me to it!]

HEADERS += $${FFTW3_LIB_PATH}/fftw3.h

...

HEADERS += \
    $${QWT_INCL_PATH}/qwt.h \
    $${QWT_INCL_PATH}/qwt_plot_spectrogram.h \
    $${QWT_INCL_PATH}/qwt_scale_map.h

Do not add 3rd-party library headers to HEADER. Instead, add their folders to INCLUDEPATH.

By adding the files to HEADER, you are asking the toolchain to compile the headers into your binaries. This causes errors if the headers contain any definitions that have already been built into the 3rd party DLL. This also causes Qt's code generator (moc) to generate a new copy of the QObjects that are found in the headers, which breaks the signal-slot mechanism (among other things) for the library.

LIBS += -L$${QWT_LIB_PATH}/ -lqwt

This is not strictly necessary, but the cleanest way to use Qwt in your project is to write include(C:/QWT/Qwt-6.1.3/features/qwt.prf) in your *.pro file. You can then get rid of all the other Qwt-related lines.

[ad5xj]

Thanks for the QWT tip I will try that.

As to the fftw3 dlls ... I did have it the way you describe and the linker complains. With some experimentation, I did find the current syntax to work. It may not be as expected but it works. Go figure.

I have had little nor no problem with QWT. No error messages about the QWT .dlls at all.

[SGaist]

What exact error do you still have with Qwt ?

[JKSH]

@ad5xj said in QtCreator 4.1.0 Qt 5.7.0 Windows 10 MinGW problem:

With some experimentation, I did find the current syntax to work. It may not be as expected but it works. Go figure.

When you say "it works", do you mean everything builds and links correctly? Or that the linker doesn't complain about missing libraries? There's a difference.

A typo in -l gets reported directly by your toolchain. Example:

LIBS += -L"C:/FFTW3/" -lfftw4-4

...

ld.exe: cannot find -lfftw4-4

In contrast, a typo in -L does not get detected or reported directly. Instead, you just get the generic "undefined reference" errors.

Anyway, note also that:

• -L is for specifying a folder that the linker should search

  • -LC:/FFTW3/libfftw3-3.dll makes your toolchain look inside a folder called "C:/FFTW3/libfftw3-3.dll/"... which probably doesn't exist (but the toolchain doesn't tell you that)

• -l is for specifying a filename root

  • -lFoo makes your toolchain link against a file called libFoo.dll (inside the folders specified by -L)

As to the fftw3 dlls ... I did have it the way you describe and the linker complains.

Please try again, especially with hard-coded paths. Then, post your unmodified .pro file and error messages.

[ad5xj]

Sorry for being ambiguous. I mean to say the linker finds the libraries and tries to link. Whereas before it could not find the libraries -lfftw3-3.dll or -lfftw3.

I understand your explanation to be the expected. I am only reporting the actual results of repeated attempts with failure before hitting on what works even if it is not what "should" be correct.

BTW SGiast I do not now, nor ever have had a problem with QWT libraries during the compile and link process. Sorry if I was not clear before.

[JKSH]

@ad5xj said in QtCreator 4.1.0 Qt 5.7.0 Windows 10 MinGW problem:

Sorry for being ambiguous. I mean to say the linker finds the libraries and tries to link.

No worries. So, does that mean all problems are gone now?

[ad5xj]

Well I do not know how to answer you JKSH.

It seems the LIBS statement is not interpreting the path and .dll name correctly for FFTW3 dll's. As you pointed out earlier, if the correct syntax is used, the linker does not find the libraries. When specified as -L<path>/<libname.dll> the linker seems to find the libraries and tries to link with them. Not sure if that is a bug in the Windows 32 bit version of qmake or something else. It needs to work as advertised but doesn't.

I also notice that if a substitution like $$FFTW3_LIB_PATH is used but not defined, the qmake hangs indefinitely without giving a message. Something new I just discovered.

I will also say that in desperation, I have uninstalled Qt, cleaned the registry and file system, and reinstalled Qt with no change in the problem.

At this point I believe the LIBS problem is a bug and possibly the substitution problem as well.

[JKSH]

@ad5xj said in QtCreator 4.1.0 Qt 5.7.0 Windows 10 MinGW problem:

When specified as -L<path>/<libname.dll> the linker seems to find the libraries and tries to link with them.

How do you know that the linker found the libraries? What messages do you get?

If you see "Undefined references", that means your linker couldn't find the libraries.

I also notice that if a substitution like $$FFTW3_LIB_PATH is used but not defined, the qmake hangs indefinitely without giving a message. Something new I just discovered.

Hmm... sounds like a bug, but I wouldn't worry about it for now.

At this point I believe the LIBS problem is a bug and possibly the substitution problem as well.

That's why I asked you to get rid of substitution and use hard-coded paths like LIBS += -LC:/FFTW3 -lfftw3-3

You can also try LIBS += C:/FFTW3/libfftw3-3.dll (don't write "-L")

Well I do not know how to answer you JKSH.

The answer is, "No, the problems are not yet gone" ;)

We'll get there eventually, I'm sure.

[kshegunov]

@ad5xj said in QtCreator 4.1.0 Qt 5.7.0 Windows 10 MinGW problem:

It seems the LIBS statement is not interpreting the path and .dll name correctly for FFTW3 dll's.

What statement are you using? One doesn't link to .dll files, and one doesn't need a path to a .dll file for linkage.

When specified as -L<path>/<libname.dll> the linker seems to find the libraries and tries to link with them.

That most certainly isn't true. -L is for specifying only additional link directories.

It needs to work as advertised but doesn't.

How is it advertised?

[ad5xj]

JKSH

I created a much smaller sub-project with only one form (mainwindow) and tested to see what would happen with the two different LIBS statements.

When stated: LIBS += -L$${FFTW3_LIB_PATH}/ -llibfftw3-3.dll

The linker does not find the dll.

When stated: LIBS += -L$${FFTW3_LIB_PATH}/libfftw3-3.dll

The linker finds the dll and successfully links the exe. It does run as expected.

However, in the larger project, this approach does not work - it does have the undefined reference error messages for the FFTW3 functions with the latter form of the LIBS statement and does not find the dlls (link output - file not found) with the former.

kshegunov

Your message seems contradictory to the thread messages so far. I have tried to eliminate the LIBS statement referencing the dlls but that does not even work at all.

[kshegunov]

Contradictory? Redundant is more like it. Let me quote a couple:

@VRonin said in QtCreator 4.1.0 Qt 5.7.0 Windows 10 MinGW problem:

also you never set the LIBS variable

LIBS += -L$${QWT_LIB_PATH} -L$${QWT_LIB_PATH} -lfftw3-3 -lqwt

@kshegunov said in QtCreator 4.1.0 Qt 5.7.0 Windows 10 MinGW problem:

should be:

LIBS += -L$${FFTW3_LIB_PATH} -lfftw3-3 -lfftw3l-3 -lfftw3f-3

And then I added:

And you should have the appropriate .lib (or .a if you're using mingw) files in $${FFTW3_LIB_PATH}.

Here's the qmake variable reference, as you can see yourself there's no guesswork involved in all this.

[JKSH]

@ad5xj said in QtCreator 4.1.0 Qt 5.7.0 Windows 10 MinGW problem:

However, in the larger project, this approach does not work

Did you set $${FFTW3_LIB_PATH} to different values in the 2 different projects?

C:/FFTW3/ is not equal to C:/FFTW3

When stated: LIBS += -L$${FFTW3_LIB_PATH}/ -llibfftw3-3.dll

The linker does not find the dll.

That should be -lfftw3-3, not -llibfftw3-3.dll

[ad5xj]

kshegunov

You must be confused. The thread has moved far past the VRonin post.

As to your reference to the qmake variable reference; here is the quote from the docs:

"LIBS
Specifies a list of libraries to be linked into the project. If you use the Unix -l (library) and -L (library path) flags, qmake handles the libraries correctly on Windows (that is, passes the full path of the library to the linker). The library must exist for qmake to find the directory where a -l lib is located.
For example:

unix:LIBS += -L/usr/local/lib -lmath
win32:LIBS += c:/mylibs/math.lib
"
You can plainly see the full pathname including the file name is in the LIBS statement. I understand the example is a static library reference and not a dll but there is no such distiinction made - with or without the .dll extension.

I did not feel that LIBS += $${FFTW3_LIB_PATH}/libfftw3-3.dll violated that example. It seems you have another idea and I would like to hear it. I am just looking for the correct way to get this done. The docs do not seem to contradict my use of the above statement, but I am open to a different way of doing it. Doing what you indicate does not work either.

I have -- several times at suggestions from other posts -- eliminated the dll reference from the .pro file. As stated this does not work.

Now, whether this is a bug or some quirk of qmake I do not know. I just want it to work.

JKSH

No. The same .pri was used to define the variables in the sub-project. So no there essentially no difference in the variable substitution value.

[kshegunov]

@ad5xj said in QtCreator 4.1.0 Qt 5.7.0 Windows 10 MinGW problem:

You must be confused.

I must have been.

[JKSH]

@ad5xj said in QtCreator 4.1.0 Qt 5.7.0 Windows 10 MinGW problem:

I did not feel that LIBS += $${FFTW3_LIB_PATH}/libfftw3-3.dll violated that example.

OK, first things first: I'm seeing small but important inconsistencies in your various posts, such as:

• LIBS += -L$${FFTW3_LIB_PATH}/libfftw3-3.dll vs.
• LIBS += $${FFTW3_LIB_PATH}/libfftw3-3.dll

...and...

• -lfftw3-3 vs.
• -llibfftw3-3.dll

It's not clear to me: Are those are typos in this thread, or did you tried both in your .pro file?

another idea ... I would like to hear it.

I've mentioned this a few times before, but I haven't seen you try it yet: Hard code your paths.

• LIBS += -LC:/FFTW3 -lfftw3-3 and/or
• LIBS += C:/FFTW3/libfftw3-3.dll

Also, close Qt Creator, delete your *.pro.user file, delete your build-* folder, and then try building from scratch.

No. The same .pri was used to define the variables in the sub-project. So no there essentially no difference in the variable substitution value.

I don't see any *.pri files in this thread. Please post your latest *.pro and *.pri files.

[ad5xj]

SUCCESS!

It seems I was so focused on the problem I did not listen to the complete answer enough to put it all together.

Before your last post JKSH I did go back and combine all the permutations of the posted suggestions. It winds up that your last post is exactly what I got to work completely.

I want to thank all of you for your patience.

But this does raise some questions. Why is the qmake syntax check so dumb? Why is the Linux qmake so different and even overly forgiving of what could be common mistakes like this (yes I am admitting it is my mistake)? Why default path checking to the linker when that is way too late?

Oh well, I don't run things at Digia so this is what we have. Thanks to all and i really do appreciate this forum.

[JKSH]

@ad5xj said in QtCreator 4.1.0 Qt 5.7.0 Windows 10 MinGW problem:

SUCCESS!

Awesome :)

Don't keep us in suspense: What was the missing ingredient?

It seems I was so focused on the problem I did not listen to the complete answer enough to put it all together.

Moral of the story: Be systematic; Try every suggestion one by one, and provide feedback one by one.

Why is the qmake syntax check so dumb?

You provided valid qmake syntax. qmake simply passes your parameters on to the linker.

qmake does not truly understand what the linker wants or needs. (It's the same principle as writing your own custom MAKEFILE: The make tool simply calls the commands that you specified, but it can't check your parameters)

I agree that it would be nice if the linker could give better feedback.

Why is the Linux qmake so different and even overly forgiving of what could be common mistakes like this (yes I am admitting it is my mistake)?

The Linux qmake is the same as the Windows qmake -- they have the same source code.

However, Linux binaries are structured differently from Windows binaries. As a result, Windows needs to resolve 3rd-party function calls at build-time, but Linux only needs to do that at load-time (when you run the application).

Why default path checking to the linker when that is way too late?

Again, qmake's job is to pass your parameters to the relevant low-level tools (and it supports many many different kinds of tools). It doesn't make sense to ask it to check your parameters.

[ad5xj]

Ok, as I explained...I tried the individual suggestions one at a time. But what I did not do is mentally connect several that wound up being the solution:

As to qmake; quite often qmake emits console messages in the Application Output tab when there are syntax error unliike the ones I mentioned. In this case I was thinking that it should be possible for qmake to determine a problem with errors in the LIBS line just the same. Evidently not.

Ok, if qmake is the same on Linux as Windows then it has to be the GCC g++ compiler or linker that is so different. Something is different because they certainly do not produce the same indications with the same code.

In any event I can now proceed and it is thanks to all of you.