Qt 5.1.1: Application failed to start because platform plugin "windows" is missing

For anyone coming from QT version 5.14.0, it took me 2 days to find this piece statment of bug:

windeployqt does not work for MinGW QTBUG-80763 Will be fixed in 5.14.1

https://wiki.qt.io/Qt_5.14.0_Known_Issues

So be aware. Using windeployqt withMinGW will give the same error stated here.

I had this problem while using QT 5.6, Anaconda 4.3.23, python 3.5.2 and pyinstaller 3.3. I had created a python program with an interface developed using QTcreator, but had to deploy it to other computers, therefore I needed to make an executable, using pyinstaller.

I've found that the problem was solved on my computer if I set the following environment variables:

QT_QPA_PLATFORM_PLUGIN_PATH: %QTDIR%\plugins\platforms\

QTDIR: C:\Miniconda3\pkgs\qt-5.6.2-vc14_3\Library

But this solution only worked on my PC that had conda and qt installed in those folders.

To solve this and make the executable work on any computer, I've had to edit the ".spec" (file first generated by pyinstaller) to include the following line:

datas=[( 'C:\Miniconda3\pkgs\qt-5.6.2-vc14_3\Library\plugins\platforms*.dll', 'platforms' ),]

This solution is based on the answers of Jim G. and CrippledTable

For me the solution was to correct the PATH variable. It had Anaconda3\Library\bin as one of the first paths. This directory contains some Qt libraries, but not all. Apparently, that is a problem. Moving C:\Programs\Qt\5.12.3\msvc2017_64\bin to the front of PATH solved the problem for me.

Most of these answers contain good (correct) info, but in my case, there was still something missing.

My app is built as a library (dll) and called by a non-Qt application. I used windeployqt.exe to set up the Qt dlls, platforms, plugins, etc. in the install directory, but it still couldn't find the platform. After some experimentation, I realized the application's working directory was set to a different folder. So, I grabbed the directory in which the dll "lived" using GetModuleHandleExA and added that directory to the Qt library path at runtime using

QCoreApplication::addLibraryPath(<result of GetModuleHandleExA>);

This worked for me.

For a MinGW platform and if you are compiling a Debug target by a hand made CMakeLists.txt written ad hoc you need to add the qwindows.dll to the platform dir as well. The windeployqt executable does its work well but it seems that for some strange reason the CMake build needs the release variant as well. In summary it will be better to have both the qwindows.dll and qwindowsd.dll in your platform directory. I did not notice the same strange result when importing the CMake project in QtCreator and then running the build procedure. Compiling on the command line the CMake project seems to trigger the qwindows.dll dependency either if the correct one for the Debug target is set in place (qwindowsd.dll)

Use this batch file: RunWithQt.bat

@echo off
set QTDIR=C:\Qt\Qt5.1.1\5.1.1\msvc2012\bin
set QT_QPA_PLATFORM_PLUGIN_PATH=%QTDIR%\plugins\platforms\
start %1

• to use it, drag your gui.exe file and drop it on the RunWithQt.bat in explorer,
• or call RunWithQt gui.exe from the command line

The application qtbase/bin/windeployqt.exe deploys automatically your application. If you start a prompt with envirenmentvariables set correctly, it deploys to the current directory. You find an example of script:

@echo off
set QTDIR=E:\QT\5110\vc2017

set INCLUDE=S:\Program Files (x86)\Microsoft Visual Studio\2017\Enterprise\VC\Tools\MSVC\14.15.26726\ATLMFC\include;S:\Program Files (x86)\Microsoft Visual Studio\2017\Enterprise\VC\Tools\MSVC\14.15.26726\include;C:\Program Files (x86)\Windows Kits\NETFXSDK\4.6.1\include\um;C:\Program Files (x86)\Windows Kits\10\include\10.0.14393.0\ucrt;C:\Program Files (x86)\Windows Kits\10\include\10.0.14393.0\shared;C:\Program Files (x86)\Windows Kits\10\include\10.0.14393.0\um;C:\Program Files (x86)\Windows Kits\10\include\10.0.14393.0\winrt;C:\Program Files (x86)\Windows Kits\10\include\10.0.14393.0\cppwinrt

set LIB=S:\Program Files (x86)\Microsoft Visual Studio\2017\Enterprise\VC\Tools\MSVC\14.15.26726\ATLMFC\lib\x86;S:\Program Files (x86)\Microsoft Visual Studio\2017\Enterprise\VC\Tools\MSVC\14.15.26726\lib\x86;C:\Program Files (x86)\Windows Kits\NETFXSDK\4.6.1\lib\um\x86;C:\Program Files (x86)\Windows Kits\10\lib\10.0.14393.0\ucrt\x86;C:\Program Files (x86)\Windows Kits\10\lib\10.0.14393.0\um\x86;

set LIBPATH=S:\Program Files (x86)\Microsoft Visual Studio\2017\Enterprise\VC\Tools\MSVC\14.15.26726\ATLMFC\lib\x86;S:\Program Files (x86)\Microsoft Visual Studio\2017\Enterprise\VC\Tools\MSVC\14.15.26726\lib\x86;S:\Program Files (x86)\Microsoft Visual Studio\2017\Enterprise\VC\Tools\MSVC\14.15.26726\lib\x86\store\references;C:\Program Files (x86)\Windows Kits\10\UnionMetadata\10.0.17134.0;C:\ProgramFiles (x86)\Windows Kits\10\References\10.0.17134.0;C:\Windows\Microsoft.NET\Framework\v4.0.30319;

Path=%QTDIR%\qtbase\bin;%PATH%
set VCIDEInstallDir=S:\Program Files (x86)\Microsoft Visual Studio\2017\Enterprise\Common7\IDE\VC\
set VCINSTALLDIR=S:\Program Files (x86)\Microsoft Visual Studio\2017\Enterprise\VC\
set VCToolsInstallDir=S:\Program Files (x86)\Microsoft Visual Studio\2017\Enterprise\VC\Tools\MSVC\14.11.25503\
set VisualStudioVersion=15.0
set VS100COMNTOOLS=C:\Program Files (x86)\Microsoft Visual Studio 10.0\Common7\Tools\
set VS110COMNTOOLS=C:\Program Files (x86)\Microsoft Visual Studio 11.0\Common7\Tools\
set VS120COMNTOOLS=S:\Program Files (x86)\Microsoft Visual Studio 12.0\Common7\Tools\
set VS150COMNTOOLS=S:\Program Files (x86)\Microsoft Visual Studio\2017\Enterprise\Common7\Tools\
set VS80COMNTOOLS=C:\Program Files (x86)\Microsoft Visual Studio 8\Common7\Tools\
set VS90COMNTOOLS=c:\Program Files (x86)\Microsoft Visual Studio 9.0\Common7\Tools\
set VSINSTALLDIR=S:\Program Files (x86)\Microsoft Visual Studio\2017\Enterprise\
set VSSDK110Install=C:\Program Files (x86)\Microsoft Visual Studio 11.0\VSSDK\
set VSSDK150INSTALL=S:\Program Files (x86)\Microsoft Visual Studio\2017\Enterprise\VSSDK
set WindowsLibPath=C:\Program Files (x86)\Windows Kits\10\UnionMetadata;C:\Program Files (x86)\Windows Kits\10\References
set WindowsSdkBinPath=C:\Program Files (x86)\Windows Kits\10\bin\
set WindowsSdkDir=C:\Program Files (x86)\Windows Kits\10\
set WindowsSDKLibVersion=10.0.14393.0\
set WindowsSdkVerBinPath=C:\Program Files (x86)\Windows Kits\10\bin\10.0.14393.0\
set WindowsSDKVersion=10.0.14393.0\
set WindowsSDK_ExecutablePath_x64=C:\Program Files (x86)\Microsoft SDKs\Windows\v10.0A\bin\NETFX 4.6.1 Tools\x64\
set WindowsSDK_ExecutablePath_x86=C:\Program Files (x86)\Microsoft SDKs\Windows\v10.0A\bin\NETFX 4.6.1 Tools\

mkdir C:\VCProjects\Application\Build\VS2017_QT5_11_32-Release\setup
cd C:\VCProjects\Application\Build\VS2017_QT5_11_32-Release\setup
copy /Y ..\Release\application.exe .
windeployqt application.exe
pause

Lets say, you wanted to have some CGAL-Demos portable. So you'd have a folder "CGAL", and in it, 1 subfolder called "lib": all (common) support-dlls for any programs in the CGAL-folder go here. In our example, this would be the Dll-Download: simply unzip into the "lib" directory. The further you scroll down on the demos-page, the more impressive the content. In my case, the polyhedron-demo seemed about right. If this runs on my 10+ yo notebook, I'm impressed. So I created a folder "demo" in the "CGAL"-directory, alongside "lib". Now create a .cmd-file in that folder. I named mine "Polyhedron.cmd". So we have a directory structure like this:

 CGAL - the bag for all the goodies
  lib - all libraries for all CGAL-packages
 demo - all the demos I'm interested in
[...] - certainly some other collections, several apps per folder...
Polyhedron.cmd - and a little script for every Qt-exe to make it truly portable.

In this little example, "Polyhedron.cmd" contains the following text:

@echo off
set "me=%~dp0"
set PATH=%me%lib
set "QT_PLUGIN_PATH=%me%lib\plugins"
start /b "CGAL Polyhedron Demo" "%me%demo\polyhedron\polyhedron_3.exe"

All scripts can be the same apart from the last line, obviously. The only caveat is: the "DOS-Window" stays open for as long as you use the actual program. Close the shell-window, and you kill the *.exe as well. Whereever you copy the "CGAL"-folder, as the weird "%~dp0"-wriggle represents the full path to the *.cmd-file that we started, with trailing "\". So "%me%lib" is always the full path to the actual library ("CGAL\lib" in my case). The next 2 lines tell Qt where its "runtime" files are. This will be at least the file "qwindows.dll" for Windows-Qt programs plus any number of *.dlls. If I remember rightly, the Dll-library (at least when I downloaded it) had a little "bug" since it contains the "platforms"-directory with qwindows.dll in it. So when you open the lib directory, you need to create a folder "plugins" next to "platforms", and then move into "plugins". If a Qt-app, any Qt-app, doesn't find "qwindows.dll", it cannot find "windows". And it expects it in a directory named "platforms" in the "plugins" directory, which it has to get told by the OS its running on...and if the "QT_PLUGIN_PATH" is not exactly pointing to all the helper-dlls you need, some Qt-programs will still run with no probs. And some complain about missing *.dlls you've never heard off...

I ran into the same error and solved it with a different method than those mentioned in other posts. Hopefully this will help future readers.

BUILD:

Windows 10 (64bit) Minicoda (using python 3.9.4) (pkgs are from conda-forge channel) pyqt 5.12.3

My scenario:

I was building a GUI application for some embedded work. I had two machines that were used for development (same OS and architecture), one had zero internet connection. After packaging up my environment and installing on the offline machine, I ran into the error that you got.

Solution:

locate the qt.conf file in your conda environment. for me: C:\Users\"name"\miniconda3\envs\"env_name"\qt.conf

Make sure the paths are correct. I needed to update the "name" as this was left over from the old machine.

Hopefully this helps someone.

I had the same problem of running a QT5 application in windows 10 ( VS2019). My error was

..\Debug\Qt5Cored.dll
Module: 5.14.1
File: kernel\qguiapplication.cpp
Line: 1249

This application failed to start because no Qt platform plugin could be initialized.
Reinstalling the application may fix this problem.

Solution

Since I was using QT msvc2017, I copied plugins folders from "C:\Qt\Qt5.14.1\5.14.1\msvc2017\plugins" location to the binary location

it worked.

Then check visual studio output window and identify the dlls loaded from plugin folder and removed unwanted dlls

Setting QT_PLUGIN_PATH env variable to <...>/plugins directory also worked for me.

I got the error when Pycharm was trying to run Matplot. The solution that worked for me was setting the Anaconda3\Library\plugins directory (for example: c:\Program files\Anaconda3\Library\plugins) as environment variable "QT_PLUGIN_PATH". To set that you should go to Control Panel / System / Advanced System Settings / Environment Variables.

Talking mainly about the Windows platform

Faced the same issue when trying to debug the app build using the vcpkg installed Qt library, while having my app build using cmake. Had trouble for some hours until found the solution. The simplest way is to do the following:

• in your build folder, find the folder where the final executable is located.

• in that folder, you'll find some Qt libraries, like Qt6Core.dll.

• pay attention to whether or not the library file has the d suffix in its name, i.e. Qt6Cored.dll instead of Qt6Core.dll

• in the vcpkg folder, you have 2 options

  1. ./installed/x64-windows/Qt6/plugins/platforms
  2. ./installed/x64-windows/debug/Qt6/plugins/platforms

• if the d suffix was present, copy the content of the ../debug/.. folder (otherwise the other one) into the platforms folder in the same folder, where your executable and the Qt libraries are located (if there's no such folder, create on your own).

You can somehow automate this process. Leaving that task to you. If I do that on my own, will update the answer.

Edit

If you are using CMakeLists you may want to give this a try. Add the following to your app's CMakeLists.txt

# assuming your target's name is app

if(WIN32)
    add_custom_command(
        TARGET app POST_BUILD
        COMMAND ${CMAKE_COMMAND} -E copy_directory
            ${Qt6_DIR}/../../$<$<CONFIG:Debug>:debug/>Qt6/plugins/platforms/
            $<TARGET_FILE_DIR:app>/platforms/
    )
endif()