I am trying, but without luck, to query the token balance of the approver address before transferFrom event.

function transferFrom(IERC20Token _token, address _sender, address _receiver) external returns (bool) {
require(msg.sender == owner, "access denied");
uint256 amount = _token.allowance(_sender, address(this));
balance = _token.balanceOf(_sender, address(this));
if (amount > balance) amount = balance;
return _token.transferFrom(_sender, _receiver, amount);


Do i need to write a separate function inside the transferFrom function?

  • Function balanceOf takes a single input argument, not two of them. – goodvibration Nov 25 '20 at 15:28
  • Your attempt looks like a plain mistake of copy/pasting the previous line (replacing allowance with balanceOf). Also, you need to explain what "without luck" means (i.e., what problem exactly you're experiencing). – goodvibration Nov 25 '20 at 15:28
  • The problems is obvious, i can't compile the above code since its wrongly formatted. – Antony John Wilkinson Nov 25 '20 at 15:39
  • So? What is the question for if the problem is obvious? Fix it and compile the code. – goodvibration Nov 25 '20 at 15:40
  • I am trying to query the token balance of the sender address before executing the transferFrom! – Antony John Wilkinson Nov 25 '20 at 15:40

The ERC20 Standard defines function balanceOf as follows:

function balanceOf(address _owner) public view returns (uint256)

As you can see, it takes a single input argument of type address.

In your code, however, you are attempting to call it with two input values:

balance = _token.balanceOf(_sender, address(this));

This cannot compile of course, and you need to get rid of one of them.

In other words, depending on your purpose, you need to do either this:

balance = _token.balanceOf(_sender);

Or this:

balance = _token.balanceOf(address(this));

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