send ether from one contract to another automatically

Question

I want to transfer ether from Child Contract to Parent Contract automatically whenever someone send ether to child.

In fallback function i tried to run the function and it is giving error: VM error: revert. revert The transaction has been reverted to the initial state. Note: The constructor should be payable if you send value. Debug the transaction to get more information.

Please tell me where i am doing wrong, i tried to run it by allocating more gas too, no luck.

Here is the code.

pragma solidity ^0.4.18;

contract ParentCompany{
    address public parentAddress;

    function ParentCompany() public{
        parentAddress = msg.sender;
    }
    function getB() public view returns(uint){
        return this.balance;
    }

    function() payable {
    }
}

// Subsidiary will automatically transfer received ether to Parent.
contract Subsidiary{

    address public subsidiaryAddress;
    address parentCompany;
    function Subsidiary(address _parentCompany) public payable{
        subsidiaryAddress = msg.sender;
        parentCompany = _parentCompany;
    }

    function sendToParent() public {
        parentCompany.transfer(this.balance);
    }
    function() payable{

        sendToParent();  
    }
}

// when Fallback function is empty it works fine.

// client will send money to Subsidiary Company
contract Client{
    address clientAddress;

    function Client() public payable{
        clientAddress = msg.sender;
    }
    function payment(address _subCompany, uint _amount) public{
        uint amount = _amount *(10**18);
        _subCompany.transfer(amount);
    }

}

Answer 1

transfer only forwards a very small amount of gas (2300). This is not enough to make a second transfer.

I believe using call in Client should work as a replacement for transfer:

require(_subCompany.call.value(amount)());