Bitcoin-qt -how does it choose the address to take money from when sending btcs

Question

I don't have any bitcoins yet, but I have the the wallet program called bitcoin-qt. I am wondering about the send feature. It does not seem to let me choose which address to deduct the coins from. How does that work?

Let's say I have 5 addresses and one coin in each and I want to send 5 coins. Does it automatically take 1 coin from each of the addresses? What if I want to take coins only from specific addresses?

Actually now looking at it more closely it doesn't even show which address contains coins and which one doesn't. Isn't this a bit oversimplified?

Answer 1

Addresses are not accounts. The quantity of coins in a given address is usually meaningless, and only in specialized circumstances there exists a reason to choose a particular address to send from.

For example, if your first Bitcoin transaction ever was receiving 100 BTC, and then you sent 1 BTC, the balance of your receiving address will be 0, because the other 99 BTC will be sent to a new change address which you've never seen. Also, the "total balance" of an address is an abstraction on top of the collection of unspent outputs to this address.

The Bitcoin client chooses which outputs to use for sending with some algorithm designed to make the transaction as simple as possible (See What is the coin selection algorithm? for discussion of the algorithm).

The Bitcoin command line (but not the GUI) supports accounts, which are an internal abstraction not recognized by the network. In addition you can use multiple wallet files, and Armory supports this with the GUI.

Answer 2

There's a patch awaiting merging into the Satoshi client which allows you to see the balance on each address and pick which address(es) you want to pay from.

See here for more description and a video of it in action.

Lots of people have been showing their support for this feature by posting "+1" comments on the pull request despite requests that they stop doing so.