Solidity function receiving value, passing it to another contract function

Question

I'm trying to create a contract which receives value to a function called contribute.

Then I shall call another contract function with value. I wonder how this is done, it's not very clear.

This is the code I got so far (all other functions and variables are left out for simplicity):

contract Hub {
    function contribute(address _address) payable {
       Project project = Project(_address);
       project.fund.value(msg.value)();
    }
}

contract Project {
    function fund(address sender) payable {
       amount += msg.value;
       contributors[sender] = msg.value;
    }
}

This gives me invalid opcode for some reason. What might be wrong? Am I trying to do it wrong?

Opcode stack is here: https://gist.github.com/vongohren/160b61e5fd2b6c0c85fb8829aed9b3b2

Answer 1

fund requires a parameter, so try passing an argument to it:

project.fund.value(msg.value)(msg.sender)

---

By not passing an argument, Solidity probably tries to look for a function fund that takes no parameters, and it won't find and thus will invoke the fallback function, which in turn will cause an internal exception via invalid opcode if it isn't payable.

Answer 2

The problem for me was that I did not send enough gas. I figured this out with different ways, but the main problem was that since I call another contracts method, which costed more gas then sent. It threw a invalid op code, and not out of gas.

So it might be smart to specifiy gas usage aswell in your contract that will call other contracts, so that the user will get a proper feedback. This way if, not sending enough gas to the main contract, that will be the proper error! Not an bogus invalid opcode error.