Qt static linking and deployment

I wrote a guide to static linking

andHow to build Qt static with multiple compilers and keep it small

(because it can get pretty big, especially for simple programs).You may also want to check out the BitRock installer, which is free for open source projects.

In short, it turns out to be a little more complex if you are using anything Qt thinks of as a plugin, such as support for most image types (JPEG, GIF) or databases.For example, if you want to include support for Oracle DBMS and GIF images for your icons, you add the following to your .PRO file:

QTPLUGIN += qsqloci qgifCONFIG += static

You will then need to:

#include <QtPlugin>

in your project, and import any plugins used. You need to change these settings back order to get it to compile with dynamic linking again (like when debugging or adding features), though this can be easily automated. There are also considerations when building the Qt libraries for use with static linking, though the Qt instructions will at least get you started.

With Qt 5.5, things are quite easy. There are following orthogonal settings that you pass to configure when building Qt:

1. Do you want a static Qt library?

   -static option should be passed to configure

2. Do you want the build of Qt, and of your application, to use a static C++ runtime?

   -static-runtime option should be passed to configure

3. Do you want XP targeting?

   -target xp option should be passed to configure

   Additionally, follow the instructions from this blog post.

   Qt Creator didn't support XP targeting automagically at least until v.3.5.0 since it doesn't set up the environment for the build tools properly. You have to modify the build environment manually per the blog post.

Also, be aware that your static build will still link to the visual studio runtimes dynamically!

See this faq (internet archive link, in case the link goes away) :

Why does a statically built Qt use the dynamic Visual Studio runtime libraries ? Do I need to deploy those with my application ?

Qt is built using the -MD(d) switch, which links against the dynamic C/C++ runtime libraries. This is necessary as we have experienced memory problems when using anything but the -MD(d) flag, and in general, it is recommended to use. You should not alter this flag yourself for your application, because it conflicts with how the Qt library is built if you change the flag to -MT. You should not change it for Qt either, since it is likely to cause problems.

Qt is still built statically when using the -static option though, meaning you do not need to distribute the Qt dlls when deploying your application. You will have to distribute the C runtimes though (if they don't already exist on the target machine), see our deployment documentation http://doc.qt.io/qt-5/windows-deployment.html#application-dependencies.