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

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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
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);