Problem when adding webp.lib.

MyNameIsQt · 16 Mar 2023, 18:20

I'm making a tool to convert images to webp.
I added the .lib as follows, but I get an error.

win32:CONFIG(release, debug|release): LIBS += -L$$PWD/webp/ -llibwebp
else:win32:CONFIG(debug, debug|release): LIBS += -L$$PWD/webp/ -llibwebpd
else:unix: LIBS += -L$$PWD/webp/ -llibwebp

QImageReader reader(fileName);
    if (fileName.toLower().endsWith(".webp")) {
        reader.setFormat("WEBP");
    }

Christian Ehrlicher · 17 Mar 2023, 08:34

@JonB said in Problem when adding webp.lib.:

cannot find -libwebpd

This is an error from MinGW so the OP is using MinGW which means libwebp.lib will not work since this is an import lib for MSVC.
And -lwebp will be correctly change to the correct linker option for MSVC iirc but this doesn't matter here. For MinGW it must be -lwebp.

Don't know if webp is a c++ or c library but when it's a c++ library then it must be compiled with the same compiler. If it's a c library then on can try to directly link against the dll with MinGW when there is no correct import library (libwebp.a) available. Or create on with the help of pexports and friends.

JonB · 17 Mar 2023, 03:37

@MyNameIsQt
It always helps to say what the error is when you get one.

-llibwebp

Did you see something which told you to type this? Not, say, -lwebp? I don't know, I'm just guessing.

MyNameIsQt · 17 Mar 2023, 05:17

@JonB
I'm sorry.
I should have posted more detailed results.
I forgot.

cannot find -libwebpd

Thanks

jsulm · 17 Mar 2023, 05:53

@MyNameIsQt said in Problem when adding webp.lib.:

-libwebpd

This is wrong.
It should be: -lwebp
-l is a parameter, what comes afterwards is the name of the library, but without lib prefix and file name extension.

MyNameIsQt · 17 Mar 2023, 06:33

@jsulm Thank.
-lwebp gives the same result.
When I build it after explicitly writing and modifying it as follows, it builds normally. But I haven't loaded the webp image yet. When you load an image, you don't know what processing result will be displayed. thank you

win32:CONFIG(release, debug|release): LIBS += -L$$PWD/webp/libwebp
else:win32:CONFIG(debug, debug|release): LIBS += -L$$PWD/webp/libwebp
else:unix: LIBS += -L$$PWD/webp/libwebp

INCLUDEPATH += $$PWD/webp
DEPENDPATH += $$PWD/webp

Christian Ehrlicher · 17 Mar 2023, 15:54

@MyNameIsQt said in Problem when adding webp.lib.:

win32:CONFIG(release, debug|release): LIBS += -L$$PWD/webp/libwebp
else:win32:CONFIG(debug, debug|release): LIBS += -L$$PWD/webp/libwebp
else:unix: LIBS += -L$$PWD/webp/libwebp

Now you don't link at all to the webp library...

Please do what we suggested and also show us what's in $$PWD/webp/libwebp

JonB · J JonB 16 Mar 2023, 18:20

@MyNameIsQt

@JonB said in Problem when adding webp.lib.:

-lwebp

Bonnie · 17 Mar 2023, 08:21

Hey guys, if OP downloaded libwebp from https://developers.google.com/speed/webp/docs/precompiled, the precompiled lib file for Windows is named libwebp.lib, so it is ok to use -llibwebp :)
And from the content he post, he must have used "Add Library..." wizard in Qt creator and chose the libwebp.lib file from a file dialog.
The problem is he left the Add "d" suffix for debug version option checked (may be default), so Qt creator add an extra "d" for debug version, which is wrong in this case.

JonB · 17 Mar 2023, 08:30

@Bonnie
Hi @Bonnie, you are doubtless correct, you usually are! But then I don't understand various things:

Doesn't it depend on which compiler/linker he is using, which he doesn't say?
Doesn't MinGW treat -l... as requiring the leading lib... be removed like under Linux?
I still don't get how -llibwebp or -llibwebpd could give the verbatim error message cannot find -libwebpd he quotes, they are not the same string?

Christian Ehrlicher · 17 Mar 2023, 08:34

@JonB said in Problem when adding webp.lib.:

cannot find -libwebpd

This is an error from MinGW so the OP is using MinGW which means libwebp.lib will not work since this is an import lib for MSVC.
And -lwebp will be correctly change to the correct linker option for MSVC iirc but this doesn't matter here. For MinGW it must be -lwebp.

Don't know if webp is a c++ or c library but when it's a c++ library then it must be compiled with the same compiler. If it's a c library then on can try to directly link against the dll with MinGW when there is no correct import library (libwebp.a) available. Or create on with the help of pexports and friends.

JonB · wrote on 17 Mar 2023, 08:34

@Christian-Ehrlicher said in Problem when adding webp.lib.:

This is an error from MinGW so the OP is using MinGW which means libwebp.lib will not work since this is an import lib for MSVC.

Thank you!

Bonnie · J JonB 17 Mar 2023, 08:21

@JonB
Yes, if he uses -llibwebp the error message should be cannot find -llibwebpd. I think he copied his version of message in the middle of trying to modify the LIBS.
The standard file name for -lname in MinGW should be name.lib or libname.a. I think older MinGW will need -llibwebp instead of -lwebp for a libwebp.lib file, but more recent versions can accept both.

BTW I'm also very confused with OP, if he is using QImageReader/QImageWriter to read/write .webp file, there's no need to link libwebp at all, because Qt uses its own webp plugin.

MyNameIsQt · wrote on 17 Mar 2023, 15:37

@Christian-Ehrlicher I use Qt.6.0.0 MinGW 64-bit kit

MyNameIsQt · wrote on 17 Mar 2023, 15:54

@Christian-Ehrlicher However, when recompiling with MSVC, many errors occur. I don't know how to handle this.