Topic: Question about change addresses and confirmation times (Read 1162 times)

Brilliant, thanks for that very clear explanation. I think I *may* now have understood transaction malleability for the first time as well which is a bonus! I haven't carried out many transactions - and definitely never tried simultaneous transactions - so I had no idea that that sort of functionality was availability in some wallets. Thanks everyone for your input on this. It's can be hard to find definitive answers some times so everyone's help is really appreciated. If people get it wrong, all well and good - then more of us get to learn the right answers 

Am sorry , am still learning but i tried my best to answer him
Thank you for clarifying it a bit more for me too

It's always entertaining watching newbies that don't know what they are talking about trying to explain what they incorrectly assume to other newbies.

odolvlobo is correct.  To a certain extent it depends on the wallet software you are using.  There are a few important points to be aware of though:

You can encounter complications if you spend bitcoins that have not yet confirmed.  A transaction uses the hash of the transaction that created the output that you are spending to identify that output. It's possible for the hash of an unconfirmed transaction to change before it becomes confirmed (This is often called "transaction malleability").  If that happens, then the second transaction will no longer be valid, and you'll need to re-send it.

In the example given, if your friend is right there with you, most wallet software will allow you to create a single transaction that has two outputs.  The single transaction can send 0.5 BTC to the coffee shop and 0.5 BTC to your friend, and you'll have no change to worry about at all.


The second transaction isn't valid in a block (can't be confirmed) until the first transaction is in a block.  Therefore, it isn't possible for the second transaction to be confirmed before the first.  They can both be confirmed in the same block (at the same time), or the first transaction can be confirmed and your friend can end up waiting for a later block for his transaction to confirm.

The initial transaction consists of sending 0.5 BTC to the coffee shop and 0.5 BTC to a change address under your wallet's control. Whether or not you can send the 0.5 BTC change before the first transaction is confirmed is up to your wallet. Some wallets let you spend unconfirmed outputs and some do not. Bitcoin Core is configurable.

PLEASE read OP again
he is considering BTC as a single unit so he can't 0.5 but 1 to get change in return just as with a dollar

¸

Well ofcourse he can spend it, its not like he's gonna send whole bitcoin for coffe and get change, he will send
only 0,5 and 0,5 will stay in his wallet, so he can send that right away and pay his friend.

Noone even needs to wait for transaction to get confirmed, it will show up really fast if he paid the fee.

cheers

He actually meansAs I understand it, that 1 Bitcoin (assuming it's a complete bitcoin, not made up of many smaller units) is used in the the first transaction for the coffee - so 0.5 bitcoin is sent to the coffee shop address whilst 0.5 bitcoin will be returned to my (new) change address.


i was unclear on it too but after he said  The money that gets returned to me is the change from the coffee shop purchase (i.e. I have to send a full 1BTC so I get 0.5 BTC change back from the coffee shop). Do I have to wait for that 0.5 BTC to be returned as change and confirmed before I use it?


he means to say if we consider BTC as a single unit just like a Dollar , the cost of coffee is 0.5 btc(50 cents) , he give 1 btc(a dollar) at coffeeshop and gets 0.5 btc back(50 cents) to his address(may be a new one as per him the account will create a new address to recieve the coins )
So yes you can use the 0.5 btc you just got to send to your Friend as soon as you get it , you don't need to wait for the confirmation

He didn't pay 1btc for the coffee. He had one btc but spent half of it on the coffee so he will have 0.5 as change. He wants to know whether he can spend that change straight away.

When you pay for coffee as 1 BTC (since it is one unit as you said) you now have 0 btc , so as soon as you get the change from them , you can send that to your friend as soon as you want , it will be no problem at all
You don't need to wait for confirmation

Interesting, thanks. I wonder if there could be an issue with the second transaction (to my friend) possibly being confirmed more quickly for some reason (better connectivity, coffee shop suffering bad connectivity etc) that then means that the second transaction (chronologically) would be picked up before the first - meaning that the coffee shop has to wait even longer to see their money.

The money that gets returned to me is the change from the coffee shop purchase (i.e. I have to send a full 1BTC so I get 0.5 BTC change back from the coffee shop). Do I have to wait for that 0.5 BTC to be returned as change and confirmed before I use it?

I think from what you're saying that yes, I could. So does that mean that the change money is returned immediately and it doesn't depend on waiting for the transaction to be included in the next block? I guess that's possible if my wallet software automatically creates a new change address that contains 0.5BTC regardless of whether my coffee shop 0.5 BTC transaction is confirmed - i.e. even if the transaction doesn't go through, I've still ended up splitting up that 1BTC in my wallet?

As far as I know, yes you can spend it although it's not yet confirmed. But the new transaction (to your friend) won't be confirmed until the previous transaction (coffee) get confirmed.

First of all You say ,
use my mobile wallet to pay my friend the 0.5 bitcoin that I owe him.
then
whilst 0.5 bitcoin will be returned to my (new) change address.


When you paid to your friend why would it return to your new address
And if you mean return to your friend's address then yes you can use the bitcoin again without waiting for confirmation(as i know cos i do it all the time)

That's actually a good question which I'd never thought of and now would like to know the answer too. I guess you could try it out for yourself and see though  .

Could someone clear up a question for me please?

I have 1 Bitcoin. I go into a coffee shop with a friend. I buy a coffee for 0.5 bitcoin (yeah, it's expensive) and then whilst waiting for the coffee to be ready, use my mobile wallet to pay my friend the 0.5 bitcoin that I owe him.

Ignore transaction fees for a minute. As I understand it, that 1 Bitcoin (assuming it's a complete bitcoin, not made up of many smaller units) is used in the the first transaction for the coffee - so 0.5 bitcoin is sent to the coffee shop address whilst 0.5 bitcoin will be returned to my (new) change address.

Question: can I spend that 0.5 bitcoin that's mine (but returned to me via a new change address) before the next block is confirmed (i.e. within 10 minutes)? Or do I have to wait until my coffee purchase is confirmed before I can pay my friend?

Thanks!