How to detect the balance change in solidity

Question

In contract, there are always some storage change like token transfer. I want to detect the token transfer event. Token always store in contract mapping struct. So how can i detect the mapping change or the variables change in contract storage and recognize this is a token change event?

Answer 1

You want to detect this from outside the contract, right? For example in an application using web3.js?

In the contract, create an event with the information you want and call it when the token transfer happens.

See here for how you can then listen for that event: https://github.com/ethereum/wiki/wiki/JavaScript-API#contract-events

Answer 2

You can use this script:

function checkAllBalances() { 
  var i =0; 
  eth.accounts.forEach( function(e){
    console.log("  eth.accounts["+i+"]: " +  e + " \tbalance: " + web3.fromWei(eth.getBalance(e), "ether") + " ether"); 
    i++; 
  })
};

taken from this thread.

Edit:

From inside the contract you can't. The only block variables you have access to are mentioned here.