[Ethereum] How to call a function and to read return values from an external deployed contract address

abicontract-developmentraw-transactionsolidity

I am trying to call a function from deployed contract address using the below format

DeployedContractAddress.call(bytes4(keccak256("get(address)")),0xfffff);

But when trying to call the get(_address) using deployed contract address(without abi encoded), it should return an array. But here, it returns Boolean values true or false.

 function get(address _address) public returns (uint256[]){
 for(uint i=0;i<n;i++){
     arr[address].push(i);
 }
 return (arr);
}

Is there any simple way to get an array values without using ABI encoded?

Best Answer

According to the Solidity documentation, starting from version 0.5.0 it is possible to access the return data from a call:

address.call(bytes memory) returns (bool, bytes memory)

issue low-level CALL with the given payload, returns success condition and return data, forwards all available gas, adjustable

The data is given as a single bytes array, so you will likely want to decode it using abi.decode in order to make use of it.

Prior to version 0.5.0, you can count on the fact that the return values remains on the stack when the call() returns. They can be accessed, but you will have to use assembly.

Related Solutions

[Ethereum] get the return value of a .call from a contract from the Blockchain

Low-level calls are just a tiny bit above inline assembly, so you can use inline assembly to emulate this feature.

Something like this:

function get(address _addr, string _func) public view returns (bytes data) {
    uint len = 32;
    uint ptr;

    bytes4 sig = bytes4(keccak256(_func));
    assembly {
        ptr := mload(0x40)       
        mstore(ptr, sig)

        let result := call(5000, _addr, 0, ptr, 0x4, ptr, add(len, 0x40))

        if eq(result, 0) {
            revert(0, 0)
        }

        ptr := add(ptr, 0x40)
        mstore(0x40, add(ptr, add(len, 0x40)))
    }

    data = toBytes(ptr, len); 
}

function toBytes(uint _addr, uint _len) internal pure returns (bytes memory bts) {
    bts = new bytes(_len);
    uint btsptr;
    assembly {
        btsptr := add(bts, 0x20)
    }
    copy(_addr, btsptr, _len);
}

Solidity – Handling Unimplemented Functions in Contracts

The problem is that totalSupply() implementation is missing. Seems like autogenerated getters do not count. So you need to explicitly create the function.

contract StandardToken is Token {
    uint256 _totalSupply;

    function totalSupply() constant returns (uint256 totalSupply) {
        totalSupply = _totalSupply;
    }
}

Best Answer

Related Solutions

[Ethereum] get the return value of a .call from a contract from the Blockchain

Solidity – Handling Unimplemented Functions in Contracts

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