[Ethereum] How to get the current time in Solidity

Transactions are always executed in the block being mined. So, at any time, block.number will return the block height in which the transaction is being mined.

However, the hash of the block is not known until it is mined, and the output of transactions is part of the hash calculation, so the transaction has no access to the hash of the block being mined.

If this is any consolation, you can get the hash of the latest mined block, i.e. the one right before this block being mined with block.blockhash(block.number - 1).

Try this:

contract Test {
    uint public blockNumber;
    bytes32 public blockHashNow;
    bytes32 public blockHashPrevious;

    function setValues() {
        blockNumber = block.number;
        blockHashNow = block.blockhash(blockNumber);
        blockHashPrevious = block.blockhash(blockNumber - 1);
    }    
}

Make a transaction to setValues() then you will see that:

• blockNumber is set at that number it was mined in
• blockHashNow is set at 0x
• blockHashPrevious is set at the previous block hash indeed

The block.timestamp should indicate approximately when the block was mined. But it is only an approximation, it depends on the precision of the clock of the machines working on it, also a miner can modify it. So it is not a very secure measure of the time but for your use case should be good.

From solidity documentation

block.timestamp (uint): current block timestamp as seconds since unix epoch.

You can do something like this:

mapping(address => uint) startTime;

function start() {
    startTime[msg.sender] = now;
}

function hasElapsed() constant return (bool) {
    if (now >= startTime[msg.sender] + 60 minutes) {
        // 60 minutes has elapsed from startTime[msg.sender]
        return true;
    }
    return false;
}