user18812: Can anyone provide a clear example on how to calculate a previous transaction hash?
Say I want to create a new transaction, I get that the hash is calculated by doubling sha256 a message m, but I'm having a hard time understanding the structure of m.

user12983: You do not need to calculate previous transaction hash, because it is already known. 
To spend the previous output you just have to know

tx hash
output index in this tx
output value
output script

plus you should choose

fee
new address

then create some byte data and sign it with appropriate private key 
Good manual you can find here: How to redeem a basic Tx?

18812: <p>Can anyone provide a clear example on how to calculate a previous transaction hash?</p>

<p>Say I want to create a new transaction, I get that the hash is calculated by doubling <code>sha256</code> a message <strong>m</strong>, but I'm having a hard time understanding the structure of <strong>m</strong>.</p>
 12983: <p>You do not need to calculate previous transaction hash, because it is already known. 
To spend the previous output you just have to know</p>

<ul>
<li>tx hash</li>
<li>output index in this tx</li>
<li>output value</li>
<li>output script</li>
</ul>

<p>plus you should choose</p>

<ul>
<li>fee</li>
<li>new address</li>
</ul>

<p>then create some byte data and sign it with appropriate private key </p>

<p>Good manual you can find here: <a href="https://bitcoin.stackexchange.com/questions/3374/how-to-redeem-a-basic-tx">How to redeem a basic Tx?</a></p>
