How to call a function from an already deployed contract?

Question

I tried to use the function "Call", as described here: Calling function from deployed contract

But seems it is not working at all.

How can I call a function from an existing deployed smart contract?

I'm trying to call a simple function from an existing address that receives an address as parameter.

This is the code I'm using to call the external function:

Contract A:

function CallExternalFunction(address externalContractAddress) 
{    
    externalContractAddress.call(bytes4(sha3("FunctionX(address)")),0xfffff);
    //sends 0xfffff as input parameter to the external contract
}

The source code of the already deployed contract is like this:

Contract B:

contract test { 

mapping (address => uint256) public balanceOf; 

function test() { 

}

function FunctionX(address _address)
{
    balanceOf[_address] = 50000;    
}
}

Answer 1

Try this. Deploy the caller, and it will deploy the test contract to simplify matters.

contract Caller {

  test public t;

  function Caller() {
    t = new test();
  }

  function callIt(address theAddress)
    public
    returns(bool success)
  {
    t = test(t); <===== here the other contract address can be called t = test([OtherContractAddress]); example: test(0x12345);
    bool result = t.FunctionX(theAddress);
    return result;
  }
}

contract test { 

  mapping (address => uint256) public balanceOf; 

  function FunctionX(address _address) public returns(bool success)
  {
    balanceOf[_address] = 50000; 
    return true;
  }
}

In Remix to show it working.

You can use a similar structure for a contract that is already if you have the source code, by using and Interface contract. Here "Caller" compiler can see just enough of test {} to manage the interface.

contract Caller {

  test public t;

  // where test is deployed and the address is known
  // Pass in the address for test {}.

  function Caller(address tAddress) {
    t = test(tAddress); // address of contract t
  }

  function callIt(address theAddress)
    public
    returns(uint bal)
  {
      return t.FunctionX(theAddress);
  }
}

// This interface constant includes the function interfaces (exactly as in the "real" contract" with the fynctions undefined
// This tells the compiler how to communicate with the ABI in test{}.

contract test { 
  function FunctionX(address _address) public returns(uint balanceOf) {}
}