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What is the memory layout of a CLR class?
Coming from a C++ background, the memory layout of a C++ class with virtual functions starts with a v-table pointer, and then the data members of the class follow in memory.
Do CLR classes with virtual functions have a v-table pointer? Is this pointer the first field in the class memory layout? Are there any extra fields in a CLR class memory layout in addition to programmers’ defined data members? And what do these extra fields represent?
It’s implementation specific, but this article gives a description of what was present in the Microsoft .NET implementation, for CLR v1.1. I suspect it’s the same for CLR v2 and v4, but I couldn’t guarantee it. Look for a section called "ObjectInstance" for the details – but you may find the whole article interesting.
According to the article, there are basically two bits of header: the sync block which is used for locking, and the type reference which is basically a pointer to type information (including the vtable).
A more recent – but potentially still pre-.NET-core article is here.