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POQt, CMake, Visual Studio and Q_OBJECT in cpp files
 

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  1. POQt, CMake, Visual Studio and Q_OBJECT in cpp files
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    <p>I'm developing a large project using Qt 4.6, CMake 2.8 and Visual Studio 2008 for the Windows platform.</p> <p>As far the build system goes, it's all standard stuff: I'm using CMake's <code>QT4_WRAP_CPP</code> macro to generate moc files from header files, which are then linked into the final executable in the <code>add_executable</code> command. Everything is working as expected.</p> <p>The only restriction with this setup is that I can't define widgets or helper using <code>Q_OBJECT</code> in <em>.cpp</em> files. This would be very convenient for small, context-specific helpers classes that should appear right next to where they're used.</p> <p>I tried to pass the whole list of source files (both <em>.h</em> and <em>.cpp</em>) to <code>QT4_WRAP_CPP</code>, instead of just the header files, but that doesn't work (linking fails because some moc-related symbols are undefined).</p> <p>I think the problem is that, for a given pair of files <em>foo.h</em> and <em>foo.cpp</em>, the <code>QT4_WRAP_CPP</code> macro will generate the same moc file (<em>moc_foo.cxx</em>) in the same directory, and obviously that means the first file will be overwritten by the second one, and as a result symbols will be missing at link-time.</p> <p>Is there a way to fix or work around that problem? For instance, I tried to add a specific rule for <em>foo.cpp</em> of the form</p> <pre><code>QT4_GENERATE_MOC(directory/foo.cpp directory/foo.moc) </code></pre> <p>and then add</p> <pre><code>#include "foo.moc" </code></pre> <p>at the end of <em>foo.cpp</em>. I think this ought to work, but alas Visual Studio only allows one build rule per file, and <em>.cpp</em> files already have a build rule (compilation to object file), so this approach doesn't work, at least with Visual Studio.</p> <p>Another idea that I had was to create a new macro, say <code>QT4_WRAP_CPP_WITH_PREFIX</code>, based on <code>QT4_WRAP_CPP</code> (which is defined in <em>share/cmake-2.8/Modules/Qt4Macros.cmake</em>), that would take an additional prefix argument and would add this prefix to the generated moc files. That way, I would call <code>QT4_WRAP_CPP_WITH_PREFIX</code> twice, once for <em>.h</em> files and once for <em>.cpp</em> files, with different prefixes. What I just dislike about this approach is that I'd be messing with the internals of CMake's Qt support, instead of using the public API.</p> <p>Any better idea?</p> <p>Cheerz, Franz</p>
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    1. USFrançois Beaune
    1. USFrançois Beaune
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    1. COI'm not sure I understand this bit: "The only restriction with this setup is that I can't define widgets or helper using Q_OBJECT in .cpp files." You shouldn't ever need to run MOC on anything except header files?
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      1. POQt, CMake, Visual Studio and Q_OBJECT in cpp files
      1. USMike McQuaid
    2. COI find it convenient to occasionnally define a small helper class in a .cpp file, and not expose it outside of this .cpp file. For this I need to be able to run MOC on .cpp files. The `QT4_WRAP_CPP_WITH_PREFIX` macro approach outlined in my post works like a charm.
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      1. POQt, CMake, Visual Studio and Q_OBJECT in cpp files
      1. USFrançois Beaune
    3. CO@FrançoisBeaune - did you ever come up with a solution for this? Even for something this simple: #include <QApplication> #include <QObject> #include <iostream> class MyClass : public QObject { Q_OBJECT }; int main(int, char*[]) { MyClass myClass; return 0; } I can't figure out how to MOC it since it is in a cpp file (and I get the vtable errors when trying to build it normally).
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      1. USDavid Doria
 

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