I'm still a newbie with ethereum and I want to know if it is possible to customize the structure of a transaction in order to add extra fields like a message or an integer or anything else.

If the answer is yes, can you please give me some good hints to guide my researchs.

Thank you!

1 Answer 1


In Ethereum, payments are normal functions with value attached. That means anything you can pass to a function you can include in a payment. It's fairly common to have some data about what was bought together with the funds to pay for it.

Simple example:

function checkOut(bytes32 itemId, uint qty) payable returns(bool success) {
   // do stuff like check the math
   if(items[itemId].price * qty != msg.value) throw;
   // track inventory, status, etc.
   return true;

Example assumes a struct full of item information and checks the price * qty matches the ETH sent with the transaction (msg.value). Throw reverts state changes and gives the money back in case that check failed (error or mischief on the front-end).

This example has a payable function: http://solidity.readthedocs.io/en/develop/solidity-by-example.html#safe-remote-purchase

payable is used to explicitly declare that receiving ETH is allowed, otherwise they autotmatically reject unexpected funds for security reasons. It's a relatively new feature for non-payable functions to throw when they receive funds.

Hope it helps.

  • Thanks for this answer!! Since my goal is to customize the transactions' structure, what would you recommend me doing in the first place? Reading the solidity's documentation?
    – Everblack
    Feb 9, 2017 at 11:11
  • Where to start is a fairly loaded question. It's a strange universe and there is necessarily a bunch of stuff around the transaction that you'll need to pick up. I got the most joy early on by playing with simple examples in Browser Solidity. Suggest you keep it really simple until you get a feel for how the compiler tool works, how to interact with the contract and generally what's going on. The "Greeter" example, for instance. Don't worry about making anything useful for a while. Feb 9, 2017 at 11:37

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