Assuming that I don’t know the contract A, I just know its address, and that it has a setNumber method that I want to call it from contract B.

I want to call the function setNumber in contract A, using the method callsetNumbercontractA in contract B.

How to reproduce:

  • Deploy both contracts
  • Copy contract A address and use the function setcontract in contract B
  • Now try to use the function callsetNumbercontractA in contract B

It will fail and I can't get why.

pragma solidity 0.5.12;
contract A {
    event lmao (string);
    uint public x;
    function hello () public {
        emit lmao ('YES');
    function setNumber (uint n) public {

pragma solidity 0.5.12;
contract B{
    address public to;    
    function callcontractA () public {
    function setcontract (address x) public{
        to = x;
    function callsetNumbercontractA () public {
        // I wanna set var x (in A) to 10

Ropsten transactions:

  • ? What is missing
    – Dani69654
    Mar 31 '20 at 16:51
  • What is Looks like I can use callcontractA() but not callsetNumbercontractA () supposed to mean??? Have you looked at the code formatting??? Mar 31 '20 at 16:52
  • Sorry for that I edited my post. Hope it's more readable.
    – Dani69654
    Mar 31 '20 at 17:02
  • I've fixed it a little bit, guess you could probably fix it further. Mar 31 '20 at 17:18

There is no reasoning in your question for not using this:

contract IA {
    function setNumber(uint n) public;

contract B {
    IA public a;    
    function setContract(IA _a) public {
        a = _a;
    function setNumber() public {
  • Thanks for editing my question (I am not practical at all excuse me). As far as I understand, in order to follow you guide, I should have both contracts on the same solidity file. Is it right? In my case, the contracts are in totally different solidity files.
    – Dani69654
    Mar 31 '20 at 17:22
  • @Dani69654: I should have both contracts on the same solidity file - no you don't (do you see both contracts in my example above?). Mar 31 '20 at 17:25

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