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[Deploying Qt Applications]

# Deploying an Application on Windows

This documentation will describe how to determine which files you should include in your distribution, and how to make sure that the application will find them at run-time. We will demonstrate the procedures in terms of deploying the Plug & Paint application that is provided in Qt's examples directory.

Contents:

- Static Linking

- Building Qt Statically
- Linking the Application to the Static Version of Qt

- Shared Libraries

- Building Qt as a Shared Library
- Linking the Application to Qt as a Shared Library
- Creating the Application Package
- Visual Studio 2005 Onwards

- Application Dependencies

- Additional Libraries
- Qt Plugins

## Static Linking

If you want to keep things simple by only having a few files to deploy, i.e. a stand-alone executable with the associated compiler specific DLLs, then you must build everything statically.

### Building Qt Statically

Before we can build our application we must make sure that Qt is built statically. To do this, go to a command prompt and type the following:

     cd C:\path\to\Qt
     configure -static <any other options you need>

Remember to specify any other options you need, such as data base drivers, as arguments to `configure`. Once `configure` has finished, type the following:

     nmake sub-src

This will build Qt statically. Note that unlike with a dynamic build, building Qt statically will result in libraries without version numbers; e.g. `QtCore4.lib` will be `QtCore.lib`. Also, we have used `nmake` in all the examples, but if you use MinGW you must use `mingw32-make` instead.

Note: If you later need to reconfigure and rebuild Qt from the same location, ensure that all traces of the previous configuration are removed by entering the build directory and typing `nmake distclean` before running `configure` again.

### Linking the Application to the Static Version of Qt

Once Qt has finished building we can build the Plug & Paint application. First we must go into the directory that contains the application:

     cd examples\tools\plugandpaint

We must then run `qmake` to create a new makefile for the application, and do a clean build to create the statically linked executable:

     nmake clean
     qmake -config release
     nmake

You probably want to link against the release libraries, and you can specify this when invoking `qmake`. Now, provided that everything compiled and linked without any errors, we should have a `plugandpaint.exe` 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. You can check which libraries your application is linking against by using the `depends` tool. For more information, see the Application Dependencies section.

The Plug & Paint example consists of several components: The application itself (Plug & Paint), and the Basic Tools and Extra Filters plugins. Since we cannot deploy plugins using the static linking approach, the application we have prepared is incomplete. It 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.

## Shared Libraries

We have two challenges when deploying the Plug & Paint application using the shared libraries approach: The Qt runtime has to be correctly redistributed along with the application executable, and the plugins have to be installed in the correct location on the target system so that the application can find them.

### Building Qt as a Shared Library

We assume that you already have installed Qt as a shared library, which is the default when installing Qt, in the `C:\path\to\Qt` directory. For more information on how to build Qt, see the Installation documentation.

### Linking the Application to Qt as a Shared Library

After ensuring that Qt is built as a shared library, we can build the Plug & Paint application. First, we must go into the directory that contains the application:

     cd examples\tools\plugandpaint

Now run `qmake` to create a new makefile for the application, and do a clean build to create the dynamically linked executable:

     nmake clean
     qmake -config release
     nmake

This builds the core application, the following will build the plugins:

     cd ..\plugandpaintplugins
     nmake clean
     qmake -config release
     nmake

If everything compiled and linked without any errors, we will get a `plugandpaint.exe` executable and the `pnp_basictools.dll` and `pnp_extrafilters.dll` plugin files.

### 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:

Component | File Name
--- | ---
The executable | `plugandpaint.exe`
The Basic Tools plugin | `plugins\pnp_basictools.dll`
The ExtraFilters plugin | `plugins\pnp_extrafilters.dll`
The Qt Core module | `qtcore4.dll`
The Qt GUI module | `qtgui4.dll`

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

| VC++ 6.0 | VC++ 7.1 (2003) | VC++ 8.0 (2005)
--- | --- | --- | ---
The C run-time | `msvcrt.dll` | `msvcr71.dll` | `msvcr80.dll`
The C++ run-time | `msvcp60.dll` | `msvcp71.dll` | `msvcp80.dll`

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 Onwards

When deploying an application compiled with Visual Studio 2005 onwards, there are some additional steps to be taken.

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 dependencies that are different from the application using it, the manifest file needs to be embedded into the DLL binary. Since Qt 4.1.3, the follwoing `CONFIG` options are available 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.

There are two ways to include the run time libraries: by bundling them directly with your application or by installing them on the end-user's system.

To bundle the run time libraries with your application, copy the directory

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

into the folder where your executable is, so that you are including a `Microsoft.VC80.CRT` directory alongside your application's executable. If you are bundling the runtimes and need to deploy plugins as well, you have to remove the manifest from the plugins (embedded as a resource) by adding the following line to the `.pro` file of the plugins you are compiling:

     CONFIG-=embed_manifest_dll

Warning: If you skip the step above, the plugins will not load on some systems.

To install the runtime libraries on the end-user's system, you need to include the appropriate Visual C++ Redistributable Package (VCRedist) executable with your application and ensure that it is executed when the user installs your application.

For example, on an 32-bit x86-based system, you would include the vcredist_x86.exe executable. The vcredist_IA64.exe and vcredist_x64.exe executables provide the appropriate libraries for the IA64 and 64-bit x86 architectures, respectively.

Note: The application you ship must be compiled with exactly the same compiler version against the same C runtime version. This prevents deploying errors caused by different versions of the C runtime libraries.

## 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 Dependency Walker 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, and note that each type of plugin should be located within a specific subdirectory (such as `imageformats` or `sqldrivers`) within your distribution directory, as described below.

Note: If you are deploying an application that uses QtWebKit to display HTML pages from the World Wide Web, you should include all text codec plugins to support as many HTML encodings possible.

The search path for Qt plugins is hard-coded into the QtCore library. By default, the plugins subdirectory of the Qt installation is the first plugin search path. However, pre-determined paths like the default one have 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 `qt.conf`. This approach is the recommended if you have executables in different places sharing the same plugins.
- Using QApplication::addLibraryPath() or QApplication::setLibraryPaths(). This approach is recommended if you only have one executable that will use the plugin.
- Using a third party installation utility to change the hard-coded paths in the QtCore library.

If you add a custom path using QApplication::addLibraryPath it could look like this:

     qApp->addLibraryPath("C:/customPath/plugins");

Then qApp->libraryPaths() would return something like this:

"C:/customPath/plugins " "C:/Qt/4.5.1/plugins" "E:/myApplication/directory/"

The executable will look for the plugins in these directories and the same order as the QStringList returned by qApp->libraryPaths(). The newly added path is prepended to the qApp->libraryPaths() which means that it will be searched through first. However, if you use qApp->setLibraryPaths(), you will be able to determend which paths and in which order they will be searched.

The How to Create Qt Plugins document outlines the issues you need to pay attention to when building and deploying plugins for Qt applications.

[Deploying Qt Applications]