Deploying an Application on Qt/Windows

Creating the Application Package

To deploy the application, we must make sure that we copy the relevant Qt DLL (corresponding to the Qt modules used in the application) as well as the executable to the same directory in the release subdirectory.

Remember that if your application depends on compiler specific libraries, these must be redistributed along with your application. You can check which libraries your application is linking against by using the depends tool. For more information, see the Application Dependencies section.

We'll cover the plugins shortly, but first we'll check that the application will work in a deployed environment: Either copy the executable and the Qt DLLs to a machine that doesn't have Qt or any Qt applications installed, or if you want to test on the build machine, ensure that the machine doesn't have Qt in its environment.

If the application starts without any problems, then we have successfully made a dynamically linked version of the Plug & Paint application. But the application's functionality will still be missing since we have not yet deployed the associated plugins.

Plugins work differently to normal DLLs, so we can't just copy them into the same directory as our application's executable as we did with the Qt DLLs. When looking for plugins, the application searches in a plugins subdirectory inside the directory of the application executable.

So to make the plugins available to our application, we have to create the plugins subdirectory and copy over the relevant DLLs:

    plugins\pnp_basictools.dll
    plugins\pnp_extrafilters.dll

An archive distributing all the Qt DLLs and application specific plugins required to run the Plug & Paint application, would have to include the following files:

In addition, the archive must contain the following compiler specific libraries depending on your version of Visual Studio:

To verify that the application now can be successfully deployed, you can extract this archive on a machine without Qt and without any compiler installed, and try to run it.

An alternative to putting the plugins in the plugins subdirectory is to add a custom search path when you start your application using QApplication::addLibraryPath() or QApplication::setLibraryPaths().

    qApp->addLibraryPath("C:\some\other\path");

One benefit of using plugins is that they can easily be made available to a whole family of applications.

It's often most convenient to add the path in the application's main() function, right after the QApplication object is created. Once the path is added, the application will search it for plugins, in addition to looking in the plugins subdirectory in the application's own directory. Any number of additional paths can be added.

Visual Studio 2005

When deploying an application compiled with Visual Studio 2005 there are some additional considerations that need to be handled.

First, we need to copy the manifest file created when linking the application. This manifest file contains information about the application's dependencies on side-by-side assemblies, such as the runtime libraries. The manifest file needs to be copied into the same folder as the application executable. You do not need to copy the manifest files for shared libraries (DLLs), since they are not used. If the shared library has different dependencies than the application using it, the manifest file needs to be embedded into the DLL binary. In Qt 4.1.3 and later we have the following CONFIG options for embedding manifests:

    embed_manifest_dll
    embed_manifest_exe

To use the options, add

    CONFIG += embed_manifest_exe

to your .pro file. The embed_manifest_dll option is enabled by default.

You can find more information about manifest files and side-by-side assemblies at the MSDN website.

We also need to include the runtime libraries. To do this, copy the contents of

    <Visual Studio Install Path>\VC\redist\<Architecture>\Microsoft.VC80.CRT

into the folder where your executable is.

Application Dependencies

Additional Libraries

Depending on configuration, compiler specific libraries must be redistributed along with your application. You can check which libraries your application is linking against by using the depends tool. To use the depends tool, all you need to do is to run it like this:

    depends <application executable>

This will provide a list of the libraries that your application depends on and other information.

When looking at the release build of the Plug & Paint executable (plugandpaint.exe) with the depends tool, the tool lists the following immediate dependencies to non-system libraries:

Qt	VC++ 6.0	VC++ 7.1 (2003)	VC++ 8.0 (2005)	MinGW
QTCORE4.DLL - The QtCore runtime QTGUI4.DLL - The QtGui runtime	MSVCRT.DLL - The C runtime MSVCP60.DLL - The C++ runtime (only when STL is installed)	MSVCR71.DLL - The C runtime MSVCP71.DLL - The C++ runtime (only when STL is installed)	MSVCR80.DLL - The C runtime MSVCP80.DLL - The C++ runtime (only when STL is installed)	MINGWM10.DLL - The MinGW run-time

When looking at the plugin DLLs the exact same dependencies are listed.

Qt Plugins

Your application may also depend on one or more Qt plugins, such as the JPEG image format plugin or a SQL driver plugin. Be sure to distribute any Qt plugins that you need with your application.

The search path for Qt plugins (as well as a few other paths) is hard-coded into the QtCore library. By default, the first plugin search path will be hard-coded as C:\path\to\Qt\plugins. Using pre-determined paths has certain disadvantages. For example, they may not exist on the target machine. For that reason you need to examine various alternatives to make sure that the Qt plugins are found:

• Using QApplication::addLibraryPath() or QApplication::setLibraryPaths().
• Using a third party installation utility to change the hard-coded paths in the QtCore library.
• Using qt.conf. This is the recommended approach since it provides the most flexibility.

[Deploying Qt Applications]