I have a 7 year old wallet.dat file that was created by the bitcoin-qt program (https://bitcoin.org/en/bitcoin-core/).
Downloading the blockchain takes too long and I experienced that the downloaded chain risks getting corrupted. I decided to use Electrum so I can access the wallet's contents sooner.
I tried following the steps from https://en.bitcoin.it/wiki/Transferring_coins_from_Bitcoin-Qt_to_Electrum, but I'm stuck at the step
dumpprivkey, because I don't know what
<your bitcoin address> means. I have installed a new bitcoin-qt version so naturally the list of receiving addresses is empty.
I have also tried another approach with
dumpwallet. This yields a 250 kb file with thousands of lines and I don't know what to do with that. Surely sweeping every single private key from that file isn't feasible?
Edit: with the command
listreceivedbyaddress 0 true bitcoin-qt shows all addresses that once received bitcoin. I supplied them to the
dumpprivkey function in order to get the corresponding private keys. This allowed me to finish the steps as described in the wiki article.