E2449 Size of 'identifier' is unknown or zero (C++)

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This identifier was used in a context where its size was needed.

A struct tag might only be declared (the struct not defined yet), or an extern array might be declared without a size.

It's illegal then to have some references to such an item (like sizeof) or to dereference a pointer to this type.

Rearrange your declaration so that the size of 'identifier' is available.