How to Resolve \'Undefined Reference to vtable\' Error in Qt Projects?

Qt Project Undefined Reference to vtable: Resolving the issue

When compiling a Qt project using Code::Blocks and the mingw compiler, an "undefined reference to vtable" error may arise. This error occurs due to missing or incomplete linkage information for a virtual method table (vtable).

To resolve this issue, it is necessary to ensure proper vtable generation during the compilation process. In the provided example, the issue pertains to the AddressBook class. The class definition in AddressBook.h declares the Q_OBJECT macro, which is responsible for generating the vtable. However, the AddressBook.cpp source file does not include the #include header, which is essential for the proper generation of the vtable.

To fix this issue, add the following line at the beginning of AddressBook.cpp:

<code class="cpp">#include <QObject></code>

This will include the necessary header and allow the compiler to generate the vtable correctly. The error should then be resolved.

For Qt Creator users, the issue can be resolved by triggering a rebuild through the following steps:

1. Select "Build" → "Run qmake".
2. Select "Build" → "Rebuild All".

This will force the generation of the Makefiles and recompile the project, ensuring proper vtable generation.

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