VM Exception while executing eth_estimateGas using for loop

Question

Important:

• Using Solidity IDE with Web3 provider
• Test RPC and web3 installed
• Testing with 10 Ether accounts with enough Ether (100 ETH) per account.

I am testing a simple contract that receives Ether from one account, splits the value and transfers it to 3 other accounts.

contract testContract {

    address[] employees = [
        0x4cd28d9a0d66216382ad3e1c993797989d1a8e05,
        0xb871e16d7192cbaa2b5be32f85c1a19f61b8a50d,
        0x5e5527378c42b91e95fee2cfbe974259d983a99e
    ];

    function testContract() payable {

    }

    function () payable {
        uint amountPerEmployee = msg.value / employees.length;

        for(uint i = 0; i <= employees.length; i++) {
            employees[i].transfer(amountPerEmployee);
        }
    }

} 

When running the callback function with the loop I get an error:

callback contain no result Error: Error: VM Exception while executing eth_estimateGas: invalid opcode at /usr/local/lib/node_modules/ethereumjs-testrpc/build/cli.node.js:59368:17 at /usr/local/lib/node_modules/ethereumjs-testrpc/build/cli.node.js:69306:5 at /usr/local/lib/node_modules/ethereumjs-testrpc/build/cli.node.js:11335:9 at /usr/local/lib/node_modules/ethereumjs-testrpc/build/cli.node.js:7895:16 at replenish (/usr/local/lib/node_modules/ethereumjs-testrpc/build/cli.node.js:8415:25) at iterateeCallback (/usr/local/lib/node_modules/ethereumjs-testrpc/build/cli.node.js:8405:17) at /usr/local/lib/node_modules/ethereumjs-testrpc/build/cli.node.js:8380:16 at /usr/local/lib/node_modules/ethereumjs-testrpc/build/cli.node.js:11332:13 at /usr/local/lib/node_modules/ethereumjs-testrpc/build/cli.node.js:69302:9 at /usr/local/lib/node_modules/ethereumjs-testrpc/build/cli.node.js:63982:7

When testing the callback function like below, everything goes well:

function () payable {
    uint amountPerEmployee = msg.value / employees.length;

    // Test with only the first item in the array, no loop
    employees[0].transfer(amountPerEmployee);
}

What is going on here? Is it the loop that is using too much gas?

Answer 1

You're walking off the end of the array with

for(uint i = 0; i <= employees.length; i++)

employees[] has exactly 3 rows, which are: 0, 1, 2.

You let i be 3 which does not exist so it isn't happy.

A related tip for later as you go forward. You'll want to refactor the loop out of the picture completely for scalability reasons.

Hope it helps.