How to create shared object library using qt C++

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Hi,

I have a requirement to create a shared object library(.so) for qt project C++. I have to use this library in another project. Means the functions I have to call from another project.

Can you please help me to how to create a library. I am using Qt4.7 version in Linux environment.

What I have tried:

Example:
I have a project abc.pro
abc.cpp contains abc::display() function

Now I have another project xyz.pro
xyz.cpp contains xyz::show() function
So from show() function I have to call display function and I have to use abc project as abc.so as a library.
How to make it possible.

Posted 31-Mar-19 23:59pm

Member 13740197

Updated 1-Apr-19 1:44am

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11917640 Member 1-Apr-19 10:23am

If you are using Qt Creator, it has "C++ Library" item in the File - New File or Project dialog.

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Richard MacCutchan · Accepted Answer · 2019-04-01T01:45:00

Solution 1

The same way you create any shared object library: linux create shared object - Google Search[^].

Posted 1-Apr-19 1:45am

Richard MacCutchan

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Member 13740197 1-Apr-19 9:04am

Thanks for the reply.
The link which you have sent is giving an explanation about creating a library using .c files. But in my case, the whole qt project(which consists of default classes and functions because of this I could not convert into .cpp files) should convert into a library.

Richard MacCutchan 1-Apr-19 9:39am

It does not matter what language the source code is in C or C++, the shared object library is created from the resulting objects. I would suggest you read the man pages for the ld(1): GNU linker - Linux man page[^].

Member 13740197 2-Apr-19 6:37am

I have tried with object files like below
gcc -shared -o libc.so camcapture.o capture-win.o ctrl-tab.o designer.o general-tab.o glMsgDialog.o json.o main.o qrc_rsc.o qv4l2.o v4l2-api.o

But I am getting below error

/usr/bin/ld: camcapture.o: Relocations in generic ELF (EM: 40)
/usr/bin/ld: camcapture.o: Relocations in generic ELF (EM: 40)
/usr/bin/ld: camcapture.o: Relocations in generic ELF (EM: 40)
/usr/bin/ld: camcapture.o: Relocations in generic ELF (EM: 40)
/usr/bin/ld: camcapture.o: Relocations in generic ELF (EM: 40)
/usr/bin/ld: camcapture.o: Relocations in generic ELF (EM: 40)
/usr/bin/ld: camcapture.o: Relocations in generic ELF (EM: 40)
/usr/bin/ld: camcapture.o: Relocations in generic ELF (EM: 40)
camcapture.o: error adding symbols: File in wrong format
collect2: error: ld returned 1 exit status

What is this error and do I need to do anything to do with ld command and object files.

Richard MacCutchan 2-Apr-19 8:46am

Like it says, the object file is in the wrong format.

Member 13740197 3-Apr-19 4:56am

Actually the object files I have taken from qt project folder after building.

Richard MacCutchan 3-Apr-19 10:48am

Well they are still in the wrong format.

Member 13740197 5-Apr-19 3:33am

Hi
I got a solution for this. I have created a library project with qt using New project->OtherProject->C++ Library. After building the project four shared libraries are created in the project folder like abc.s0, abc.so.1, abc.so.1.0 and abc.so.1.0.0.

I used this libraries in another project which is successfully run. After running that exe in target I got error below

./mycam: error while loading shared libraries: abc.so.1: cannot open shared object file: No such file or directory

What is this error and how to resolve it, Can you please help.

Richard MacCutchan 5-Apr-19 11:11am

The message is quite clear. You are trying to reference a file that the loader cannot find. You need to add the path of these files to the system search path for libraries, or copy them all to the same location as the executable program.

Member 13740197 8-Apr-19 8:29am

Thanks for the reply, now I am able to run my application. But I got another issue. My library contains GUI which uses resource file for images.
And I have added this resource file in my application also, but when I am running my application these images are not displaying. So how to make it possible to display, Can you please help.

Richard MacCutchan 8-Apr-19 23:50pm

Sorry, no, because I have no ide how your code works. Please edit your question and provide some proper details.

Member 13740197 9-Apr-19 1:25am

The below is some part of the code which is used in the library.

m_capStartAct = new QAction(QIcon(":/images/record.png"), "&Start capturing", this);
QAction *quitAct = new QAction(QIcon(":/images/exit.png"), "&Quit", this);
QToolBar *toolBar = addToolBar("");
toolBar->setObjectName("toolBar");
toolBar->addAction(m_capStartAct);
toolBar->addAction(quitAct);

Here the images record.png & exit.png are present in resource file rsc.qrc.

But when I am using this library in another application the images are not displaying(means empty button) and function is working fine. I have added these images to my application as a resource file but still, images are not displaying. Can you please help me.

Richard MacCutchan 10-Apr-19 0:01am

That is QT code, and unfortunately I have not used it at all. I can only assume the resource paths are not correct for every application.

How to create shared object library using qt C++

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