SdfFileFormat class is not DLL exported

[jerry-huxtable-foundry]

The class SdfFileFormat is not marked as SDF_API. Its methods are marked as SDF_API though. This means that although the methods are exported, the type_info and vtable etc. aren't. When trying to write a file format plugin and subclassing SdfFileFormat, on Windows this causes a compiler warning:

warning C4275: non dll-interface class 'pxrInternal_v0_25_8__pxrReserved__::SdfFileFormat' used as base for dll-interface class 'MySuperFileFormat'

SdfFileFormat is the class with which we've encountered this problem. I suspect there are other public API classes which also exhibit it.

[spiffmon]

Hi @jerry-huxtable-foundry , we reckon this is happening because you are exporting your entire, derived class? Per our coding guidelines, we advise exporting the individual, public, non-inlined methods, as OpenUSD itself does.

[jesschimein]

Filed as internal issue #USD-11793

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[jerry-huxtable-foundry]

Thanks for the useful reply. We are indeed exporting the entire class. We note that other file formats, such as the Adobe plugins, are exporting the classes and copied the usage.

[spiffmon]

Ah, tagging @dlarsson-adobe on that, as presumably their windows users are getting the same warnings.