Mastering Blockchain Programming with Solidity

The balanceOf function

The balanceOf() function returns the token balance of the given address. The balances of each account are maintained in a mapping. This function just returns the uint256 balance data from the mapping. 

The following is the API of the balanceOf() function:

function balanceOf(address who) external view returns (uint256 balance);

The balanceOf() function takes a single argument:

• who: The address whose token balances you want to read

The function returns the token balance as a uint256 type. The following is the function implementation, where it reads the data from the balances mapping and returns the token balance:

function balanceOf(address _owner) public view returns (uint256) {    return balances[_owner];}