[Qt-creator] Debugging helper for forward declared classes (PIMPL)

André Pönitz apoenitz at t-online.de
Sun May 12 13:54:12 CEST 2019

On Sun, May 12, 2019 at 12:42:33PM +0200, resurrection at centrum.cz wrote:
> I have a problem creating a debugging helper for classes that does use only
> forward-declared data member like when using PIMPL:

> - MyClass.h
>     struct MyClassPrivate;
>     class MyClass
>     {
>         MyClassPrivate *d;
>     };
> - MyClass.cpp
>     struct MyClassPrivate
>     {
>         int i;
>     };
>     //...
> And the debugging helper:
> def qdump__MyClass(d, value):
>     with Children(d):
>         d.putSubItem("Number", value["d"]["i"])
> Only place when debugging helper for MyClass works is in the implementation file of
> MyClass.cpp. In all other places the MyClassPrivate is just forward declared type and
> the pointer to it is completely opaque to the debugging helper engine unless I step into
> the MyClass.cpp where the type is defined.    I may be asking for the impossible, but is
> there a way to work around this somehow? 

When you know the layout of the private class, you can direcly operate on that. 
E.g.  value.split('...') e.g. works similar to Python's  struct.unpack('...')

I actually prefer this approach nowadays for rarely changing types as it does
not require any debug information for the type, just the address of an instance. 


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