Memcpy a struct in storage_var

📜 Development Proposals Starknet Technical Development
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let (result : ERC721PUT*) = alloc()
let (local _bid : ERC721PUT) = bids.read(bid_index)
memcpy(result, &_bid, ERC721PUT.SIZE) curious why this will not work? is &_bid not appropriate here ?

bids is a storage_var

I get this \nUnknown value for memory cell at address 12:12.\n assert [frame.dst] = [frame.src]\n

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Last time I had this error it was linked to the fact that the size was uncorrect.
I think this question would be answered more quickly on the discord :slight_smile:

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Just to complete the circle for anybody else. I was returning from a function the array where the result_len was based on felt and not on ERC721PUT

return (result_len, result) ← result_len was the problem.

Thanks Gaetbout

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This doesn’t work because &_bid refers to a local variable in memory, not a storage reference. bids.read(bid_index) loads the value into memory, but memcpy expects both source and destination to be valid memory addresses. _bid is a value, not a pointer. You can’t take its address like that. Instead, write each field manually or load directly into result.