Query token balance before transferFrom

Question

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?

Answer 1

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));