Qt dynamic linking

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If you have any problems with the registration process or your account login, please contact us. Remember Me? Results 1 to 7 of 7. Thread Tools Show Printable Version. I use the MinGW compiler making a Windows. Suppose you have the following libraries: 1 - Dynamic: vettore.

How should I write it for him to link the libraries to my program that do the test named main. Do not retype or simplify it. Otherwise we are all guessing the problem from a fabrication where relevant details are often missing.

To obtain a dynamic library. Lib and. Dll with QtCreator, how should I do? I can write a very simple example like Hello World? To copy to clipboard, switch view to plain text mode. Qt Code: Switch view. I discovered, however, that it is not enough that automatically creates the wizard, you have in the project file.

The linker will only expect to find a main if the template type is app. Amletos' example builds cleanly and correctly with MingW.

When you build a "lib" project with you will get a shared library by default on Linux and Windows.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service.

The dark mode beta is finally here. Change your preferences any time. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. Are there any compelling performance reasons to choose static linking over dynamic linking or vice versa in certain situations?

I've heard or read the following, but I don't know enough on the subject to vouch for its veracity. With dynamic linking only your code can be optimized. If most of the time is spent running library code, this can make a big difference. Otherwise, 1 still applies. Some edits to include the very relevant suggestions in the comments and in other answers.

I'd like to note that the way you break on this depends a lot on what environment you plan to run in. Minimal embedded systems may not have enough resources to support dynamic linking.

Slightly larger small systems may well support dynamic linking, because their memory is small enough to make the RAM savings from dynamic linking very attractive. Full blown consumer PCs have, as Mark notes, enormous resources, and you can probably let the convenience issues drive your thinking on this matter.

Classically, dynamic libraries require a some kind of glue layer which often means double dispatch or an extra layer of indirection in function addressing and can cost a little speed but is function calling time actually a big part of your running time??? However, if you are running multiple processes which all call the same library a lot, you can end up saving cache lines and thus winning on running performance when using dynamic linking relative to using static linking.

Unless modern OS's are smart enough to notice identical segments in statically linked binaries. Seems hard, anyone know? Another issue: loading time. You pay loading costs at some point.

qt dynamic linking

When you pay this cost depends on how the OS works as well as what linking you use. Maybe you'd rather put off paying it until you know you need it. Note that static-vs-dynamic linking is traditionally not an optimization issue, because they both involve separate compilation down to object files. However, this is not required: a compiler can in principle, "compile" "static libraries" to a digested AST form initially, and "link" them by adding those ASTs to the ones generated for the main code, thus empowering global optimization.

None of the systems I use do this, so I can't comment on how well it works. The way to answer performance questions is always by testing and use a test environment as much like the deployment environment as possible.

Dynamic linking is the only practical way to meet some license requirements such as the LGPL. Today, this is usually negligible. On amd64, jumps can be relative to the program counter, so this is a huge improvement. With optimizations guided by profiling you can usually win about percent performance.

Now that CPU speed has reached its limits it might be worth doing it.Due to the proliferation of Unix systems such as commercial Unixes, Linux distributions, and so ondeployment on Unix is a complex topic.

Before we start, be aware that programs compiled for one Unix flavor will probably not run on a different Unix system. For example, unless you use a cross-compiler, you cannot compile your application on Irix and distribute it on AIX.

Static linking is often the safest and easiest way to distribute an application on Unix since it relieves you from the task of distributing the Qt libraries and ensuring that they are located in the default search path for libraries on the target system. We specify the prefix so that we do not overwrite the existing Qt installation.

The example above only builds the Qt libraries, i. When linking your application against static Qt libraries, note that you might need to add more libraries to the LIBS line in your project file. For more information, see the Application Dependencies section. Once Qt is built statically, the next step is to regenerate the makefile and rebuild the application. First, we must go into the directory that contains the application:.

Now run qmake to create a new makefile for the application, and do a clean build to create the statically linked executable:. You probably want to link against the release libraries, and you can specify this when invoking qmake. Note that we must set the path to the static Qt that we just built. To check that the application really links statically with Qt, run the ldd tool available on most Unices :. Now, provided that everything compiled and linked without any errors, we should have a plugandpaint file that is ready for deployment.

One easy way to check that the application really can be run stand-alone is to copy it to a machine that doesn't have Qt or any Qt applications installed, and run it on that machine. Remember that if your application depends on compiler specific libraries, these must still be redistributed along with your application.

Since we cannot deploy plugins using the static linking approach, the executable we have prepared so far is incomplete. The application will run, but the functionality will be disabled due to the missing plugins. To deploy plugin-based applications we should use the shared library approach. Now run qmake to create a new makefile for the application, and do a clean build to create the dynamically linked executable:.

There is no standard package management on Unix, so the method we present below is a generic solution. See the documentation for your target system for information on how to create a package. To deploy the application, we must make sure that we copy the relevant Qt libraries corresponding to the Qt modules used in the applicationthe platform pluginand the executable to the same directory tree.

Remember that if your application depends on compiler specific libraries, these must also be redistributed along with your application. We'll cover the plugins shortly, but the main issue with shared libraries is that you must ensure that the dynamic linker will find the Qt libraries. Unless told otherwise, the dynamic linker doesn't search the directory where your application resides. There are many ways to solve this:. The disadvantage of the first approach is that the user must have super user privileges.

The disadvantage of the second approach is that the user may not have privileges to install into the predetermined path. In either case, the users don't have the option of installing to their home directory. We recommend using the third approach since it is the most flexible.

For example, a plugandpaint. By running this script instead of the executable, you are sure that the Qt libraries will be found by the dynamic linker. Note that you only have to rename the script to use it with other applications.

When looking for plugins, the application searches in a plugins subdirectory inside the directory of the application executable. On most systems, the extension for shared libraries is. A notable exception is HP-UX, which uses.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service. The dark mode beta is finally here.

Change your preferences any time. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. I'm developing a closed source application and to do so in accordance with the LGPL I have to dynamically link Qt's libraries to my application.

Does Qt do this by default or do I have to take steps to do so?

qt dynamic linking

If that's the case how would I go about doing it? You'll notice this immediately during deployment to a non-developer machine, because your code will not run without the Qt libraries. Most LGPL violations with Qt are not because of static linking since dynamic is the defaultbut for compiling Qt with non-default parameters. LGPL is not just that the library must be provided along your binaries, but also that you specify how your users can build themselves the LGPL part.

If you compile Qt yourself and do not use the pre-compiled binaries from the website, you must document that part of your build configuration in your release! As soon as you get something running on your program, start preparing a release version for a non-developer environment without Qt installed.

Your program should fail as soon as you delete the DLLs that you must copy along your program or whatever format your OS uses. It does it by default, statically linking seems to be quite involved judging by the many questions on the site regarding it. Learn more. Does Qt creator by default statically or dynamically link it's libraries? Ask Question. Asked 7 years, 9 months ago. Active 4 years, 10 months ago.

Viewed 9k times. Kevin Brown 33k 35 35 gold badges silver badges bronze badges. Active Oldest Votes. Qt uses dynamic linking by default. SystematicFrank SystematicFrank I haven't been able to find this information in the official documentation. Care to provide a source? Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Email Required, but never shown. The Overflow Blog. Featured on Meta. Feedback on Q2 Community Roadmap.

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Question Close Updates: Phase 1. Linked 6. Related Hot Network Questions.GitHub is home to over 40 million developers working together to host and review code, manage projects, and build software together. Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community. Already on GitHub? Sign in to your account. Since QT is lgpl, this library is pretty much unusable without being able to dynamically link QT to the go application.

Your readme. An example way to build such a dynamically linked executable would be helpful since golang is typically known for statically linked binaries. I smell a PyQT paid license coming The only exception to this is iOS, where statically linking is the only option at the moment. But this may change with 5. If the application is closed source and you dynamically link against Qt then you would need to either:.

However if your application is open source, then there are no further conditions that have to be meet. I was under the assumption that "work that uses the library" is not triggering the viral part of LGPL. Therefor it makes no difference how you comply with these conditions.

That's a FAQ and not the license itself. The license itself is not black and white when it comes to that issue. And probably also divided into different tiers. Don't get me wrong. It's good your paid and this is valuable. It's more about risk and knowing that all the code invested on top of QT golang is not going away actually too. Hi therecipefirst of all, thanks for this package.

More specifically, in my case :. LGPL license insists that end user must be able to recombine or relink the application with a modified or different version of the LGPL library, to produce a modified executable :.

This can be achieved using two method :. Because of my use case, and the fact that AFAIK Go doesn't make an object code, so my only choice is by using dynamic linking. Fortunately qtdeploy by default already dynamic links to Qt library, so I can just distribute the executable and user can install his own library. So, from what I found Qt is passable for my use case.

Now, what is the implication of using these tools and API for creating my closed and commercial app? Repeating above, LGPL license insists that end user must be able to recombine or relink the application with a modified or different version of the LGPL library, to produce a modified executable. As we know, Go compile its code into one single executable file. And since Go by default static linking all imported package, and Go AFAIK doesn't have object code, my only choice is giving him my source code, which is not allowed on my case.

There is object code created, but it's "hidden" inside some temp folder. You can preserve it by running: go build -work -x then look into the "WORK" folder. The last lines of the output are also what your user would need to run to re-link your object code against another version of the binding. Afaik, code created with qtmoc and qtrcc is yours.This tutorial illustrates different approaches for using a custom library in your application on Windows. The first part explains how to create a shared library and how to link against it in your application.

The second part is about creating and using a static library. When creating a shared library that you would like to link against, then you need to ensure that the symbols that are going to be used outside the library are properly exported when the library is created. Subsequently imported when you are linking against the library. On Windows, MinGW will output. They help link your code to the library and is needed when you build your file.

See also the documentation on Creating Shared Libraries. In order to use the shared library in your application, then you can include the headers of your library in your code and use the methods.

Compile with linking to the. At runtime this loads the dll which has the implementation. To set this up, then in your application's. In addition you need to ensure that the. QLibrary can be used for loading shared libraries at runtime. In this case you only need access to the. The following example shows how to set up a library for usage with QLibrary. For the function names to be resolvable, they must be exported as C functions i.

To load the library using QLibrary, you can simply pass in the. Make sure the. To use functions from the library in your application, you need to resolve them using QLibrary::resolve.

The example below loads the library created above and uses one of its functions to create and show a widget. In contrast to the shared library example, you don't need to set up anything special for exporting and importing symbols in your. For more information, see Installing Files. Which approach to choose depends on your needs. When creating a shared library, you need to deploy it with your application. On the plus side, applications and libraries linked against a shared library are small. Whether to use QLibrary to load the.

Static linking results in a stand-alone executable. The advantage is that you will only have a few files to deploy. The disadvantage is that the executables are large. See the Deployment documentation for more details on shared and static builds. Jump to: navigationsearch. Category : HowTo. Navigation menu Personal tools Sign in. Namespaces Page Discussion. Views Read View source View history.

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The dark mode beta is finally here. Change your preferences any time. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. After I compiled the application it didn't work for me gave errorsI searched all over the internet and found a lot of people saying that I have to copy those dlls mentioned below from the directory:.

My problem is the size of these dlls, they're about "37 MB" and my application itself is only "30 KB"!

How to create a library with Qt and use it in an application

So, those Qt libraries will add at least 37 MB to my application [ Which I don't see it happens with other Qt-based applications I download ]. Is there any solution can make me end up with a single small. Note: I've come across a lot of questions here on StackOverFlow but I couldn't find anything can help me, so please do not flag this as a duplication because if I found a clear answer I wouldn't post this question!

The simplest way to use windeployqt is to add the bin directory of your Qt installation e. Tested with Qt 5.

qt dynamic linking

So you need to manually get the last 3 dlls before deploying:. I think you may have a few extras in your list I would double check the docs in the links below The amazing Qt Libraries can do a lot, but they are kind of big.

Some of the older versions of Qt might be a little smaller. If you statically link, then your EXE should grab the libraries it needs and gets built into a stand alone exe.

It still may be dependent on msvc redistributables. See the next section for more info on it. But it now compiles down the. It does take more time to get your statically linked exe environment setup. Your exe will certainly get bigger as it now includes the binary information for the libraries that you referenced before. The only tricky requirement is keeping the ability for a third party to relink your application against a different Qt version.

But you can comply with that easily, f. Look at the chart near the bottom. If you are doing the commercial version, then you can statically link, without worrying about the object files. To find these options in the development environment, click Settings on the Project menu.

qt dynamic linking

See the Use Run-Time Library drop-down box. These two links below talk about some older versions of visual studio, but the reasoning should still stand.

How do I make a fully statically linked. It will automatically copy all the required libs and stuff into the folder, where your exe is located and you can just distribute it. For Windows you need to include qminimal. Even if you program is small you still call huge libraries to do the graphical interface. If the size is really important you should do a console project.