Method ID for a Solidity generated getter function

Question

In solidity, the bytecode for functions is taking the web3.sha3 value of a function name and taking the first 4 bytes of the resulting hash in the format of 0x00000000

So if you have a function called totalsupply() the hash would be 0x18160ddd

I have the understanding that public variables have getters automatically created.

However, when trying to determine the bytecode for a public variable such as 'Name'. I would assume the function created is 'Name()' and thus the bytecode is 0x8052474d.

However, it doesnt seem to be working when I try to call a function using that bytecode.

Any thoughts as to what I am doing wrong?

Answer 1

For a public variable x, i will automatically generate method x(), so you can access this variable the way call method. I give a simple demo, as follows:

pragma solidity ^0.4.2;

contract test{

    uint public age;

    function test(){
        age = 10;
    }

    function callData() returns (string){
        bool result = this.delegatecall(bytes4(sha3("age()")));
        if (result) {
            return "success";
        }
        return "failed";
    }

}

Hope it helps~

Answer 2

From the example in the Solidity documentation, we can see that:

0xcdcd77c0: the Method ID. This is derived as the first 4 bytes of the Keccak hash of the ASCII form of the signature baz(uint32,bool)

We can verify the hash using this online keccak 256 hash tool by inputing "baz(uint32,bool)":

https://emn178.github.io/online-tools/keccak_256.html

Also, you can get the contract ABI from etherscan, and paste it into this tool: https://abi.hashex.org/#

which provides then the hashes for your functions. It seems you need to enter at least the first parameter.

Answer 3

On solidity browser the bytecode for all functions ina contract is given. No need to break your head... Discovered it moments after posting this.