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I got a few errors when I try to access variables of a ERC20 token contract.

The contract is the "Sample fixed supply token contract" from https://theethereum.wiki/w/index.php/ERC20_Token_Standard

pragma solidity ^0.4.8;

// ----------------------------------------------------------------------------------------------
// Sample fixed supply token contract
// Enjoy. (c) BokkyPooBah 2017. The MIT Licence.
// ----------------------------------------------------------------------------------------------

// ERC Token Standard #20 Interface
// https://github.com/ethereum/EIPs/issues/20
contract ERC20Interface {
    // Get the total token supply
    function totalSupply() constant returns (uint256 totalSupply);

    // Get the account balance of another account with address _owner
    function balanceOf(address _owner) constant returns (uint256 balance);

    // Send _value amount of tokens to address _to
    function transfer(address _to, uint256 _value) returns (bool success);

    // Send _value amount of tokens from address _from to address _to
    function transferFrom(address _from, address _to, uint256 _value) returns (bool success);

    // Allow _spender to withdraw from your account, multiple times, up to the _value amount.
    // If this function is called again it overwrites the current allowance with _value.
    // this function is required for some DEX functionality
    function approve(address _spender, uint256 _value) returns (bool success);

     // Returns the amount which _spender is still allowed to withdraw from _owner
     function allowance(address _owner, address _spender) constant returns (uint256 remaining);

     // Triggered when tokens are transferred.
     event Transfer(address indexed _from, address indexed _to, uint256 _value);

     // Triggered whenever approve(address _spender, uint256 _value) is called.
     event Approval(address indexed _owner, address indexed _spender, uint256 _value);
 }

 contract FixedSupplyToken is ERC20Interface {
     string public constant symbol = "FIXED";
     string public constant name = "Example Fixed Supply Token";
     uint8 public constant decimals = 18;
     uint256 _totalSupply = 1000000;

     // Owner of this contract
     address public owner;

     // Balances for each account
     mapping(address => uint256) balances;

     // Owner of account approves the transfer of an amount to another account
     mapping(address => mapping (address => uint256)) allowed;

     // Functions with this modifier can only be executed by the owner
     modifier onlyOwner() {
         if (msg.sender != owner) {
             throw;
         }
         _;
     }

     // Constructor
     function FixedSupplyToken() {
         owner = msg.sender;
         balances[owner] = _totalSupply;
     }

     function totalSupply() constant returns (uint256 totalSupply) {
         totalSupply = _totalSupply;
         return totalSupply;
     }

    function getSymbol() returns (string) {
        return symbol;
    }  

     // What is the balance of a particular account?
     function balanceOf(address _owner) constant returns (uint256 balance) {
         return balances[_owner];
     }

     // Transfer the balance from owner's account to another account
     function transfer(address _to, uint256 _amount) returns (bool success) {
         if (balances[msg.sender] >= _amount 
             && _amount > 0
             && balances[_to] + _amount > balances[_to]) {
             balances[msg.sender] -= _amount;
             balances[_to] += _amount;
             Transfer(msg.sender, _to, _amount);
             return true;
         } else {
             return false;
         }
     }

     // Send _value amount of tokens from address _from to address _to
     // The transferFrom method is used for a withdraw workflow, allowing contracts to send
     // tokens on your behalf, for example to "deposit" to a contract address and/or to charge
     // fees in sub-currencies; the command should fail unless the _from account has
     // deliberately authorized the sender of the message via some mechanism; we propose
     // these standardized APIs for approval:
     function transferFrom(
         address _from,
         address _to,
         uint256 _amount
     ) returns (bool success) {
         if (balances[_from] >= _amount
             && allowed[_from][msg.sender] >= _amount
             && _amount > 0
             && balances[_to] + _amount > balances[_to]) {
             balances[_from] -= _amount;
             allowed[_from][msg.sender] -= _amount;
             balances[_to] += _amount;
             Transfer(_from, _to, _amount);
             return true;
         } else {
             return false;
         }
     }

     // Allow _spender to withdraw from your account, multiple times, up to the _value amount.
     // If this function is called again it overwrites the current allowance with _value.
     function approve(address _spender, uint256 _amount) returns (bool success) {
         allowed[msg.sender][_spender] = _amount;
         Approval(msg.sender, _spender, _amount);
         return true;
     }

     function allowance(address _owner, address _spender) constant returns (uint256 remaining) {
         return allowed[_owner][_spender];
     }
 }

Here are the logs of truffle console.

First I successfully deployed the contract:

truffle(development)> TestERC20.deployed().then(function(instance){contract= instance;});
undefined

Then when I try to get the name of the token, it worked as expected:

truffle(development)> contract.name.call()
'Example Fixed Supply Token'

1.But when it comes to the second variable "symbol", a error occurs. The "symbol" is exactly the same type as "name".

truffle(development)> contract.symbol.call()
Error: Invalid number of arguments to Solidity function
    at Object.InvalidNumberOfSolidityArgs (/usr/local/lib/node_modules/truffle/build/cli.bundled.js:43290:16)
    at SolidityFunction.validateArgs (/usr/local/lib/node_modules/truffle/build/cli.bundled.js:329518:22)
    at SolidityFunction.toPayload (/usr/local/lib/node_modules/truffle/build/cli.bundled.js:329534:10)
    at SolidityFunction.call (/usr/local/lib/node_modules/truffle/build/cli.bundled.js:329575:24)
    at /usr/local/lib/node_modules/truffle/build/cli.bundled.js:318032:16
    at new Promise (<anonymous>)
    at /usr/local/lib/node_modules/truffle/build/cli.bundled.js:318023:18

2.Then I try the function "totalSupply()", and it returned the same error. This is a function with no input parameters, but it response "Invalid number of arguments"?

truffle(development)> contract.totalSupply()
Error: Invalid number of arguments to Solidity function
    at Object.InvalidNumberOfSolidityArgs (/usr/local/lib/node_modules/truffle/build/cli.bundled.js:43290:16)
    at SolidityFunction.validateArgs (/usr/local/lib/node_modules/truffle/build/cli.bundled.js:329518:22)
    at SolidityFunction.toPayload (/usr/local/lib/node_modules/truffle/build/cli.bundled.js:329534:10)
    at SolidityFunction.call (/usr/local/lib/node_modules/truffle/build/cli.bundled.js:329575:24)
    at SolidityFunction.execute (/usr/local/lib/node_modules/truffle/build/cli.bundled.js:329704:22)
    at /usr/local/lib/node_modules/truffle/build/cli.bundled.js:318032:16
    at new Promise (<anonymous>)
    at /usr/local/lib/node_modules/truffle/build/cli.bundled.js:318023:18

3.Then if call the function like this, it seems works but how to print the return value?

truffle(development)> contract.totalSupply
{ [Function]
  call: [Function],
  sendTransaction: [Function],
  request: [Function: bound ],
  estimateGas: [Function] }

I'm a beginner and need some help to fix these problems. Thanks!

My environments are:

Node v9.2.0

TestRPC v6.0.3 (ganache-core: 2.0.2)

Truffle v4.0.1 (core: 4.0.1)

Solidity v0.4.18 (solc-js)

  • Random comment - deploying ERC20 is like Ethereum "Hello World"... contract.name.call() and contract.symbol.call() seem symmetrical to me, but I'm a beginner too 😇 – Mars Robertson Dec 4 '17 at 13:29
  • The problem is solved after I clean up the "build" folder and compile the contract again. It seems that the old compiled files are mixed with the new ones. – David Young Dec 4 '17 at 14:18

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