Qt Creator fails to load Qwt plugin (64-bit)



  • Hi,
    I have installed Qt 5.9.1 on Windows 7. The only installed kit is "Desktop Qt 5.9.1 MSVC2015 64-bit". Qwt-6.1.3 (64-bit) is built and installed.

    I have created a test widget using Qwt. It builds and runs without problems.

    However, when trying to modify the form using Qt Creator 4.3.1, the Qwt plugin fails to load. The Qwt widgets are not visible in the side panel. "Tools->Form Editor->About Qt Designer Plugins" reports:

    "Cannot load library C:\Qwt-6.1.3\plugins\designer\qwt_designer_plugin.dll: %1 is not a valid Win32 application"

    If I run Qt Designer (64-bit) from the Start menu ("Qt 5.9.1->5.9.1->MSVC 2015 (64-bit)->Designer"), the Qwt plugin is loaded correctly. Qwt is displayed in the side panel and can be added to the form.

    I need Qt Creator to load 64-bit plugins. Can Qt Creator be setup to load 64-bit plugins?


  • Moderators

    @frodebj If QtCreator is built as 32bit (which is the case if you use Qt Online Installer) then no you cannot use 64bit plug-ins - this just cannot work. You would need QtCreator 64 bit build.


  • Lifetime Qt Champion

    Hi and welcome to devnet,

    To add to @jsulm, you need to use the same compiler/Qt version as Qt Creator in order to build a plugin for it that it will be able to load.



  • Thanks to @jsulm and @SGaist for explaining the mismatch problem with the plugin.

    I have implemented the following work-around/solution:

    1. Built and deployed a 32-bit Qwt plugin for Qt Creator.
    2. Built a 64-bit Qwt library (.lib).
    3. Built my test widget as a 64-bit application (linking in the 64-bit Qwt library).

    Works for me :-)



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