Cannot build MySQL plugin

george · 4 Dec 2020, 09:41

Hello,
I am a hobbyist programmer and a totally newcomer to Qt, but I have moderate experience in C ++ and other SDKs
Since I want to focus on database application development for my personal needs, I tried to connect to a MySQL database. Soon I realized that I have to build, by myself, the MySQL plugin
I followed various instructions reading relative threads from this forum and watched YouTube videos. I also read the official help files (https://doc.qt.io/qt-5/sql-driver.html) of this topic, but I didn't manage to build the plugin.
I have installed the Qt 5.14.2 and the MySQL Connector to the following paths in my hard drive:
"C:\Qt" and
"C:\Program Files\MySQL\MySQL Connector C 6.1"
I think there are two methods to build the plugin. The first method is to open the corresponding project (in my case the MySQL) from the following path:
"C:\Qt\5.14.2\Src\qtbase\src\plugins\sqldrivers\mysql"
I modified the project in order to include the needed header files and include the needed libraries as follows:

but the Qt creator says that "library mysql is not defined"
The second method is the command line prompt using the qmake. The following image shows the same error:

I don't know what I am doing wrong and I am stuck. Any help will be appreciated

kshegunov · G george 15 Apr 2020, 15:46

@george said in Cannot build MySQL plugin:

Before I start, I am wondering if I have to modify the project file

You shouldn't.

I had added the following lines

Don't do that, you provide the paths on the command line, as per the documentation. Don't forget to quote the paths, as they contain spaces.

Christian Ehrlicher · wrote on 12 Apr 2020, 09:54

You did not set up your environment correct. When you use MSVC you have to open the correct visual studio command prompt. When using MinGW then it's not nmake but mingw32-make (as written in the documentation)

george · 4 Dec 2020, 18:23

Thank you for your response.

When you use MSVC you have to open the correct visual studio command prompt.

Is this the one shown in the screenshot?

SGaist · wrote on 12 Apr 2020, 18:41

Hi,

If it's the one matching the Qt version used in your Kit then yes.

george · wrote on 12 Apr 2020, 18:57

Hi SGaist,

I think it is, because I've installed only the MSVC 64bit compiler
Therefore it is not the set up of my environment, the reason I cannot build the plugin...

SGaist · wrote on 12 Apr 2020, 18:59

You should check the test logs generated to see what exactly failed when the detection ran.

george · wrote on 12 Apr 2020, 19:31

Could you please point me out where I can find these test logs?

SGaist · wrote on 12 Apr 2020, 20:03

In the folder where you call qmake.

george · 4 Dec 2020, 20:52

In the folder where you call qmake.

I call the qmake from the folder:
C:\Qt\5.14.2\Src\qtbase\src\plugins\sqldrivers\mysql
In the following image there is a list of all files. There is no log files there (all subfolders are empty)

http://www.mediafire.com/view/vgec6rp2ldmf9lh/qt%25235.jpg/file

kshegunov · G george 12 Apr 2020, 20:50

Hi,
Open the .pro file for the plugin and change the line which reads:

QMAKE_USE += mysql

to:

# QMAKE_USE += mysql

Then rerun qmake and build with make/nmake. Then you can see what the compiler complained about exactly. Do let us know, I had that problem compiling psql because I mixed the arch by accident.

george · 13 Apr 2020, 18:57

Hi kshegunov,
Although I don't know what the QMAKE_USE += mysql instruction does, I understand that the '#' symbol is for remarks
I followed your instruction.
From the command prompt, I am getting no messages, so I opened the project from the creator and there are no errors.
The compiler output window among other displays something about "win32-msvc", but I've the 64bit version installed:

20:06:46: Running steps for project mysql...
20:06:46: Starting: "C:\Qt\5.14.2\msvc2017_64\bin\qmake.exe" C:\Qt\5.14.2\Src\qtbase\src\plugins\sqldrivers\mysql\mysql.pro -spec win32-msvc "CONFIG+=debug" "CONFIG+=qml_debug"

In the following image you can see the full compiler output

http://www.mediafire.com/view/vfi179q0efuqh5t/qt%25236.jpg/file
But if everything is OK, where is the plugin? I searched for a ".dll" file in the subfolders but all they are empty

Christian Ehrlicher · wrote on 13 Apr 2020, 18:24

You did not follow the documentation - you have to run qmake in the sqldrivers subdir...

kshegunov · G george 13 Apr 2020, 17:29

@george said in Cannot build MySQL plugin:

From the command prompt, I am getting no messages, so I opened the project from the creator and there are no errors.

You didn't invoke the generated makefile as far as I could see from your screenshot. So I wouldn't expect you to see any messages. ;) After you run the qmake, you do need to call nmake to start things rolling.

@Christian-Ehrlicher said in Cannot build MySQL plugin:

You did not follow the documentation - you have to run qmake in the sqldrivers subdir...

True, but don't lose patience on us. He just tried to follow what I asked, have some faith. ;)

george · 14 Apr 2020, 11:19

First of all, I would like to thank you for spending your valuable time, reading my posts and try to guide me.
It is true that I went a step forward. First I ran the vcvarsall.bat (I did not execute this batch file before). I suppose that sets some environment variables, right?
From the command prompt and in the following directory: "C:/Qt/15.4.2/Src/qtbase/src/sqldrivers" I build the plugin as follows:

qmake -- MYSQL_INCDIR="C:/Program Files/MySQL/MySQL Connector C 6.1/include" MYSQL_LIBDIR="C:/Program Files/MySQL/MySQL Connector C 6.1/lib"

Here is the output:

http://www.mediafire.com/view/swazfssbaa0dg2u/qt%25237.jpg/file
But what is the next step?
If I enter:

nmake sub-mysql

as manual says, I am getting the following errors:

Microsoft (R) Program Maintenance Utility Version 14.16.27035.0
Copyright (C) Microsoft Corporation.  All rights reserved.

        cd mysql\ && ( if not exist Makefile C:\Qt\5.14.2\msvc2017_64\bin\qmake.exe -o Makefile C:\Qt\5.14.2\Src\qtbase\src\plugins\sqldrivers\mysql\mysql.pro ) && "C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\VC\Tools\MSVC\14.16.27023\bin\HostX64\x64\nmake.exe" -f Makefile

Microsoft (R) Program Maintenance Utility Version 14.16.27035.0
Copyright (C) Microsoft Corporation.  All rights reserved.

        "C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\VC\Tools\MSVC\14.16.27023\bin\HostX64\x64\nmake.exe" -f Makefile.Release all

Microsoft (R) Program Maintenance Utility Version 14.16.27035.0
Copyright (C) Microsoft Corporation.  All rights reserved.

        link /NOLOGO /DYNAMICBASE /NXCOMPAT /DEBUG /OPT:REF /INCREMENTAL:NO /DLL /SUBSYSTEM:WINDOWS /VERSION:5.14 /OUT:..\plugins\sqldrivers\qsqlmysql.dll @C:\Users\George\AppData\Local\Temp\nmEA57.tmp
LINK : fatal error LNK1181: cannot open input file 'lmysql.obj'
NMAKE : fatal error U1077: '"C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\VC\Tools\MSVC\14.16.27023\bin\HostX64\x64\link.EXE"' : return code '0x49d'
Stop.
NMAKE : fatal error U1077: '"C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\VC\Tools\MSVC\14.16.27023\bin\HostX64\x64\nmake.exe"' : return code '0x2'
Stop.
NMAKE : fatal error U1077: 'cd' : return code '0x2'
Stop.

kshegunov · G george 13 Apr 2020, 21:20

@george said in Cannot build MySQL plugin:

LINK : fatal error LNK1181: cannot open input file 'lmysql.obj'

Do you by any chance use a statically built Qt? This linker error is rather odd.

george · 14 Apr 2020, 17:29

@kshegunov said in Cannot build MySQL plugin:

Do you by any chance use a statically built Qt?

Hmm... How can I check this?
I searched my entire hard drive for the file "lmysql.obj", but I found nothing

Christian Ehrlicher · wrote on 14 Apr 2020, 16:58

Please make sure that there are no leftovers in the sqldrivers subdir (best is to remove this subdir and unpack it again) and try again.

kshegunov · G george 14 Apr 2020, 16:37

@george said in Cannot build MySQL plugin:

I searched my entire hard drive for the file "lmysql.obj", but I found nothing

Hence I was suspicious. How did you obtain the sources, did you clone them from git or unpacked them from an archive, or maybe installed them through the maintenance tool? Christian's advice is a good one at this point, you want to make sure there are no leftovers because that can break the build.

george · 14 Apr 2020, 17:44

I'll uninstall the Qt entirely and I'll delete the Qt folder.
Then, I'll install from scratch the SDK using the online installer (only the MSVC 64 bit compiler)
Then I'll let you know since the installation will take some time.

kshegunov · G george 14 Apr 2020, 17:40

Sounds like a plan.

@george said in Cannot build MySQL plugin:

Then, I'll install from scratch the SDK using the online installer (only the MSVC 64 bit compiler)

One one note here, make sure that the SDK architecture (and compiler) you select matches the one of your command prompt that you're going to use. I had experienced this cryptic error when I tried to compile the PSQL driver with a 64 bit msvc, while my Qt distro was for 32 bit msvc. I know it sounds silly but it's an easy error to make, and not very obvious if you actually make it.