Tutorial: Create an ERC-20 Token

 

Tutorial: Create an ERC-20 Token

 

ERC-20 Tokens are the types of tokens used in most initial coin offerings (ICOs). They are a standard type of token which is based on Ethereum, and they’re surprisingly easy to create.

To help you quickly create an ERC-20 token, I have provided the following open source code below which you can modify and use for your own purposes. (View instructional video at: https://youtu.be/b3kzi4UVdCk)

NOTE: Remix.Ethereum.Org has made some adjustments in the latest versions of the Solidity compilers and as a result you may come across an error when you compile the code. To get around this issue, select an earlier version of the compiler, preferably 0.4.24+commit.e67f0147.Emscripten.clang or earlier.

 

Create an ERC-20 Token Sample Source Code

 

Code starts below the following line.



pragma solidity ^0.4.20;

contract Token {

/// @return total amount of tokens
function totalSupply() constant returns (uint256 supply) {}

/// @param _owner The address from which the balance will be retrieved
/// @return The balance
function balanceOf(address _owner) constant returns (uint256 balance) {}

/// @notice send `_value` token to `_to` from `msg.sender`
/// @param _to The address of the recipient
/// @param _value The amount of token to be transferred
/// @return Whether the transfer was successful or not
function transfer(address _to, uint256 _value) returns (bool success) {}

/// @notice send `_value` token to `_to` from `_from` on the condition it is approved by `_from`
/// @param _from The address of the sender
/// @param _to The address of the recipient
/// @param _value The amount of token to be transferred
/// @return Whether the transfer was successful or not
function transferFrom(address _from, address _to, uint256 _value) returns (bool success) {}

/// @notice `msg.sender` approves `_addr` to spend `_value` tokens
/// @param _spender The address of the account able to transfer the tokens
/// @param _value The amount of wei to be approved for transfer
/// @return Whether the approval was successful or not
function approve(address _spender, uint256 _value) returns (bool success) {}

/// @param _owner The address of the account owning tokens
/// @param _spender The address of the account able to transfer the tokens
/// @return Amount of remaining tokens allowed to spent
function allowance(address _owner, address _spender) constant returns (uint256 remaining) {}

event Transfer(address indexed _from, address indexed _to, uint256 _value);
event Approval(address indexed _owner, address indexed _spender, uint256 _value);

}

contract StandardToken is Token {

function transfer(address _to, uint256 _value) returns (bool success) {
//Default assumes totalSupply can't be over max (2^256 - 1).
//If your token leaves out totalSupply and can issue more tokens as time goes on, you need to check if it doesn't wrap.
//Replace the if with this one instead.
//if (balances[msg.sender] >= _value && balances[_to] + _value > balances[_to]) {
if (balances[msg.sender] >= _value && _value > 0) {
balances[msg.sender] -= _value;
balances[_to] += _value;
Transfer(msg.sender, _to, _value);
return true;
} else { return false; }
}

function transferFrom(address _from, address _to, uint256 _value) returns (bool success) {
//same as above. Replace this line with the following if you want to protect against wrapping uints.
//if (balances[_from] >= _value && allowed[_from][msg.sender] >= _value && balances[_to] + _value > balances[_to]) {
if (balances[_from] >= _value && allowed[_from][msg.sender] >= _value && _value > 0) {
balances[_to] += _value;
balances[_from] -= _value;
allowed[_from][msg.sender] -= _value;
Transfer(_from, _to, _value);
return true;
} else { return false; }
}

function balanceOf(address _owner) constant returns (uint256 balance) {
return balances[_owner];
}

function approve(address _spender, uint256 _value) returns (bool success) {
allowed[msg.sender][_spender] = _value;
Approval(msg.sender, _spender, _value);
return true;
}

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

mapping (address => uint256) balances;
mapping (address => mapping (address => uint256)) allowed;
uint256 public totalSupply;
}

//name this contract whatever you'd like
contract ERC20Token is StandardToken {

function () {
//if ether is sent to this address, send it back.
throw;
}

/* Public variables of the token */

/*
NOTE:
The following variables are OPTIONAL vanities. One does not have to include them.
They allow one to customise the token contract & in no way influences the core functionality.
Some wallets/interfaces might not even bother to look at this information.
*/
string public name; //fancy name: eg Simon Bucks
uint8 public decimals; //How many decimals to show. ie. There could 1000 base units with 3 decimals. Meaning 0.980 SBX = 980 base units. It's like comparing 1 wei to 1 ether.
string public symbol; //An identifier: eg SBX
string public version = 'H1.0'; //human 0.1 standard. Just an arbitrary versioning scheme.

//
// CHANGE THESE VALUES FOR YOUR TOKEN
//

//make sure this function name matches the contract name above. So if you're token is called TutorialToken, make sure the //contract name above is also TutorialToken instead of ERC20Token

function ERC20Token(
) {
balances[msg.sender] = NUMBER_OF_TOKENS_HERE; // Give the creator all initial tokens (100000 for example)
totalSupply = NUMBER_OF_TOKENS_HERE; // Update total supply (100000 for example)
name = "NAME OF YOUR TOKEN HERE"; // Set the name for display purposes
decimals = 0; // Amount of decimals for display purposes
symbol = "SYM"; // Set the symbol for display purposes
}

/* Approves and then calls the receiving contract */
function approveAndCall(address _spender, uint256 _value, bytes _extraData) returns (bool success) {
allowed[msg.sender][_spender] = _value;
Approval(msg.sender, _spender, _value);

//call the receiveApproval function on the contract you want to be notified. This crafts the function signature manually so one doesn't have to include a contract in here just for this.
//receiveApproval(address _from, uint256 _value, address _tokenContract, bytes _extraData)
//it is assumed that when does this that the call *should* succeed, otherwise one would use vanilla approve instead.
if(!_spender.call(bytes4(bytes32(sha3("receiveApproval(address,uint256,address,bytes)"))), msg.sender, _value, this, _extraData)) { throw; }
return true;
}
}


Code ends above the line.

(Source: TokenFactory available open source under MIT License)

George Levy

George Levy is Chief Learning Officer for Blockchain Institute of Technology (BIT) and a co-founder of Bitsonline. Blockchain Institute of Technology (BIT) is one of the world’s leading Blockchain technology training providers. BIT partners with companies and individuals to address their unique needs, providing training and certification that helps professionals reach their goals. George is an award-winning digital entrepreneur, Certified Senior Blockchain Professional (CSBCP) and a Certified Bitcoin Professional (CBP). Follow George on Twitter @georgelevy and on YouTube atYouTube.com/GeorgeLevy.

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