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ERC20 Token Standard Interface を使った Smart Contractの実装について

ERC20 Token Standard Interface の紹介



やっぱり自分で何か作ってみたいと思うようになり・・Smart ContractでTokenを作ることにしました。

色々調べて、Smart ContractでTokenを作るには、ERC20 Token Standardを満たしている

今回は、その ERC20 Token Standard Interface の実装方法を紹介します。


Layout of a Solidity Source File — Solidity 0.4.14 documentationが参考になりました。

Solidity supports import statements that are very similar to those available in JavaScript (from ES6 on), although Solidity does not know the concept of a “default export”.


そこで、先ずは ERC20Interfaceの定義だけを記載した sol ファイルを作ってみます。


pragma solidity ^0.4.11;

// 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);


ERC20Interface.sol と同一のディレクトリにファイルを作成します。



  • import文にて同一ディレクトリのERC20Interface.solファイルを指定することで、ERC20Interfaceを使用することができます。
  • FixedSupplyTokenERC20Interfaceで指定されている各種のメソッドを実装する必要があります。
pragma solidity ^0.4.8;

import "./ERC20Interface.sol";

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() {
        require(msg.sender == owner);

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

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

    // 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];


throw をつかうと

Warning: "throw" is deprecated in favour of "revert()", "require()" and "assert()".

throw は使わずに、できる限り、revert, require, assert を使うようにした方がよさそうです。

↑ の例でいえば、以下の箇所で throw の使用をさけました。

modifier onlyOwner() {
    if (msg.sender != owner) {


    modifier onlyOwner() {
        require(msg.sender == owner);


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