[Ethereum] How to compare msg.data (calldata) data type to an integer data type uint256

Assume you have a solidity function inside your smart contract which accepts data in the form of e.g. an integer called xyz:

function takeData(int xyz)

Now in e.g. geth you can create an instance of that smart contract and call the function by:

contractInstance.takeData.sendTransaction(12345, {from: web3.eth.accounts[0]})

You can find a complete walk-through example which I created for our teaching efforts at Validity Labs on my github: https://github.com/SCBuergel/timeLock-smartContract

IF the fallback function only gets 2300 gas, it can't write to contract storage and here are 2 ideas.

Option 1

You could add an explicit function like receiveEther(string senderName) in the contract. web3.js can be used like contractInstance.receiveEther("name of the sender", {value: web3.toWei(1, "ether"), ...}) and the contract could access the sender name and msg.value easily without parsing the ABI.

Option 2

If you want to avoid having a function the user has to call, then in your contract fallback function you emit an event with msg.data. The app listens for the event and can then parse and store the event data in a database, or if you want to store the data in the contract, the app makes a transaction to the contract to store the data.

A difference with option1 is that storing the data in the contract is a second transaction. It is easier for the user that they don't need to call a function, but the app needs to be built robustly so that the data gets stored (whatever is listening for the event might go down).