[Qt-interest] Undefined symbol error when using singleton class with Qt plugins

[Bo Thorsen]

Den 14-01-2011 07:13, Andreas Unger skrev:
> Hi all,
>
> Attached please find a small test project consisting of a singleton 
> class with two public methods: testString() and printTestString()
>
> The plugin in the project has only one method in its interface: 
> printTestString();
>
> When Singleton::printTestString is called,  
> TestPlugin::printTestString() is called in turn. The string that is 
> printed in the plugin is this: Singleton::instance()->testString()
>
> Could someone please help me figure out why I get this error when I 
> try to run the code:
>
> ./Test: symbol lookup error: libtestplugin.so: undefined symbol: 
> _ZN9Singleton8instanceEv
>
> It seems likes the symbol relating to the static Singleton::instance() 
> method is undefined. How could I fix this? I would really appreciate 
> your input.

The problem is that your plugin uses a concrete class but doesn't have 
the symbols compiled in.

When you have a class that's used in both the main application and the 
plugins, you should put it in a library and have both of them link to it.

Bo Thorsen,
Fionia Software.

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