I define a balance as follows :

mapping (address => uint[]) Energy_Balance

to keep the history of each transaction. I set its new value as follows :

First Transaction: balances[owner][0] = balances[owner][0] + value; 
Second Transaction: balances[owner][1] = balances[owner][1] + value;

Now, I want to define a uint counter such that it can keep its last value every time it is increased one unit as follows :

balances[owner][counter] = balances[owner][counter] + value

If I define counter as follows, is it correct in solidity and it can keep its last value ?

static uint counter = 0;
function myFunction(uint value) {
    balances[owner][counter] = balances[owner][counter] + value;
    counter = counter +1;

1 Answer 1


You can simplify.

function myFunction(uint value) {

Also, some useful getters:

function getOwnerValueCount(address owner) returns(uint count) {
  return balances[owner].length;

Add public to your mapping for Energy_Balances and you will get a "free" getter approximately:

function Energy_Balances(address owner, uint row) public view returns(uint) {
  return Energy_Balances[owner][row];

Aside: It would be more conventional to camelCase energyBalances.

Hope it helps.

  • Thankyou. do you mean in case of using "energyBalances[owner].push(value);" I don't need to define energyBalances as an array like this : mapping (address => uint[]) energyBalances ?
    – Questioner
    Apr 27, 2018 at 13:10
  • No. Assuming you did. mapping (address=>uint []) means there's an array each address. push appends another row, so you don't need to manage the counter yourself. Apr 27, 2018 at 14:08

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