Understanding ERC-20 Tokens: The Ethereum Token Standard

Introduction to ERC-20 Tokens

The ERC-20 token standard defines a common interface for Ethereum smart contracts to represent tokens on the Ethereum blockchain. This standardization offers significant benefits for the development of blockchain-based applications by ensuring interoperability across various platforms.

Key Applications of ERC-20 Tokens

Wallets: All ERC-20 compliant tokens can be managed within a single wallet (e.g., MyEtherWallet, MetaMask).
Exchanges: Tokens can be traded on any exchange that supports the ERC-20 standard (e.g., Uniswap, Binance).
Block Explorers: Token balances and transfers can be tracked using tools like Etherscan or Ethplorer.

function transfer(address _to, uint256 _value) returns (bool success)

How Tokens Are Represented

Tokens are tracked using a simple balance sheet to record ownership and transfers. Below is an example of a token balance sheet for three holders (A, B, C) with a total supply of 10,000 tokens:

Owner	Token Balance
A	640
B	50
C	100
...	...
Total	10,000

Example Token Transfer

If A transfers 40 tokens to B, the balance sheet updates as follows:

Owner	Token Balance
A	600
B	90
C	100
...	...
Total	10,000

Core Attributes of an ERC-20 Token

A basic ERC-20 token contract includes four key attributes:

Name: A descriptive string (e.g., "Example Token").
Symbol: A short identifier (e.g., "EXP").
Decimals: Defines token divisibility (e.g., 18 decimal places).
Total Supply: The total number of tokens in circulation, including fractions.

Example Smart Contract

Below is a simplified Solidity contract implementing an ERC-20 token:

contract BasicERC20TokenExample {
    string public constant name = "Example Token";
    string public constant symbol = "EXP";
    uint8 public constant decimals = 18;
    uint256 public constant totalSupply = 10000 * (10 ** uint256(decimals));

    mapping(address => uint256) balances;

    function BasicERC20TokenExample() public {
        balances[msg.sender] = totalSupply;
    }

    function transfer(address _to, uint256 _value) public returns (bool) {
        require(_to != address(0));
        require(_value <= balances[msg.sender]);
        balances[msg.sender] -= _value;
        balances[_to] += _value;
        return true;
    }

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

Advanced ERC-20 Functions

Allowances and Delegated Transfers

ERC-20 tokens support allowances, enabling third parties (e.g., exchanges) to transfer tokens on behalf of holders.

Key Functions:

approve: Grants a spender the right to transfer tokens.

function approve(address _spender, uint256 _value) returns (bool success)

transferFrom: Allows the spender to transfer tokens.

function transferFrom(address _from, address _to, uint256 _value) returns (bool success)

allowance: Checks the remaining allowance for a spender.

function allowance(address _owner, address _spender) constant returns (uint256 remaining)

Security Considerations

Events: ERC-20 contracts emit Transfer and Approval events for tracking.
Approval Attack: Changing allowances atomically can prevent front-running attacks.

👉 Learn more about Ethereum smart contracts

FAQ

What is the ERC-20 standard?

The ERC-20 standard defines a set of rules for creating fungible tokens on Ethereum.

Why are ERC-20 tokens important?

They ensure compatibility across wallets, exchanges, and dApps.

How do I create an ERC-20 token?

Deploy a smart contract with the required functions (e.g., transfer, balanceOf).

What are token decimals?

Decimals determine the smallest divisible unit of a token (e.g., 18 decimals = 1e18 units per token).

Can ERC-20 tokens be swapped?

Yes, decentralized exchanges (DEXs) like Uniswap support ERC-20 token swaps.

👉 Explore top ERC-20 tokens