ERC-20 implementation in Blockchain / Solidity

Introduction

ERC-20 is a standard way to create tokens on the Ethereum blockchain. It helps different tokens work well together.

When you want to create your own digital currency or token.

When you want your token to be compatible with wallets and exchanges.

When you want to manage token balances and transfers easily.

When you want to allow others to spend tokens on your behalf.

When you want to build decentralized apps that use tokens.

Syntax

Blockchain / Solidity

pragma solidity ^0.8.0;

interface IERC20 {
    function totalSupply() external view returns (uint256);
    function balanceOf(address account) external view returns (uint256);
    function transfer(address to, uint256 amount) external returns (bool);
    function allowance(address owner, address spender) external view returns (uint256);
    function approve(address spender, uint256 amount) external returns (bool);
    function transferFrom(address from, address to, uint256 amount) external returns (bool);

    event Transfer(address indexed from, address indexed to, uint256 value);
    event Approval(address indexed owner, address indexed spender, uint256 value);
}

contract MyToken is IERC20 {
    string public name = "MyToken";
    string public symbol = "MTK";
    uint8 public decimals = 18;
    uint256 private _totalSupply;

    mapping(address => uint256) private _balances;
    mapping(address => mapping(address => uint256)) private _allowances;

    constructor(uint256 initialSupply) {
        _totalSupply = initialSupply * 10 ** decimals;
        _balances[msg.sender] = _totalSupply;
        emit Transfer(address(0), msg.sender, _totalSupply);
    }

    function totalSupply() public view override returns (uint256) {
        return _totalSupply;
    }

    function balanceOf(address account) public view override returns (uint256) {
        return _balances[account];
    }

    function transfer(address to, uint256 amount) public override returns (bool) {
        require(to != address(0), "Transfer to zero address");
        require(_balances[msg.sender] >= amount, "Not enough balance");

        _balances[msg.sender] -= amount;
        _balances[to] += amount;
        emit Transfer(msg.sender, to, amount);
        return true;
    }

    function allowance(address owner, address spender) public view override returns (uint256) {
        return _allowances[owner][spender];
    }

    function approve(address spender, uint256 amount) public override returns (bool) {
        require(spender != address(0), "Approve to zero address");

        _allowances[msg.sender][spender] = amount;
        emit Approval(msg.sender, spender, amount);
        return true;
    }

    function transferFrom(address from, address to, uint256 amount) public override returns (bool) {
        require(to != address(0), "Transfer to zero address");
        require(_balances[from] >= amount, "Not enough balance");
        require(_allowances[from][msg.sender] >= amount, "Allowance exceeded");

        _balances[from] -= amount;
        _balances[to] += amount;
        _allowances[from][msg.sender] -= amount;

        emit Transfer(from, to, amount);
        return true;
    }
}

This code uses Solidity version 0.8.0 or higher for safety features.

The contract implements the IERC20 interface to follow the ERC-20 standard.

Examples

This shows a minimal contract that promises to follow ERC-20 but needs full code.

Blockchain / Solidity

contract SimpleToken is IERC20 {
    // minimal implementation
}

This function returns how many tokens an address owns.

Blockchain / Solidity

function balanceOf(address account) public view override returns (uint256) {
    return _balances[account];
}

This function moves tokens from the sender to another address.

Blockchain / Solidity

function transfer(address to, uint256 amount) public override returns (bool) {
    require(_balances[msg.sender] >= amount, "Not enough balance");
    _balances[msg.sender] -= amount;
    _balances[to] += amount;
    emit Transfer(msg.sender, to, amount);
    return true;
}

Sample Program

This complete contract creates a token named MyToken with symbol MTK. The creator gets all tokens at the start. It supports checking balances, transferring tokens, approving others to spend tokens, and transferring tokens on behalf of others.

Blockchain / Solidity

pragma solidity ^0.8.0;

interface IERC20 {
    function totalSupply() external view returns (uint256);
    function balanceOf(address account) external view returns (uint256);
    function transfer(address to, uint256 amount) external returns (bool);
    function allowance(address owner, address spender) external view returns (uint256);
    function approve(address spender, uint256 amount) external returns (bool);
    function transferFrom(address from, address to, uint256 amount) external returns (bool);

    event Transfer(address indexed from, address indexed to, uint256 value);
    event Approval(address indexed owner, address indexed spender, uint256 value);
}

contract MyToken is IERC20 {
    string public name = "MyToken";
    string public symbol = "MTK";
    uint8 public decimals = 18;
    uint256 private _totalSupply;

    mapping(address => uint256) private _balances;
    mapping(address => mapping(address => uint256)) private _allowances;

    constructor(uint256 initialSupply) {
        _totalSupply = initialSupply * 10 ** decimals;
        _balances[msg.sender] = _totalSupply;
        emit Transfer(address(0), msg.sender, _totalSupply);
    }

    function totalSupply() public view override returns (uint256) {
        return _totalSupply;
    }

    function balanceOf(address account) public view override returns (uint256) {
        return _balances[account];
    }

    function transfer(address to, uint256 amount) public override returns (bool) {
        require(to != address(0), "Transfer to zero address");
        require(_balances[msg.sender] >= amount, "Not enough balance");

        _balances[msg.sender] -= amount;
        _balances[to] += amount;
        emit Transfer(msg.sender, to, amount);
        return true;
    }

    function allowance(address owner, address spender) public view override returns (uint256) {
        return _allowances[owner][spender];
    }

    function approve(address spender, uint256 amount) public override returns (bool) {
        require(spender != address(0), "Approve to zero address");

        _allowances[msg.sender][spender] = amount;
        emit Approval(msg.sender, spender, amount);
        return true;
    }

    function transferFrom(address from, address to, uint256 amount) public override returns (bool) {
        require(to != address(0), "Transfer to zero address");
        require(_balances[from] >= amount, "Not enough balance");
        require(_allowances[from][msg.sender] >= amount, "Allowance exceeded");

        _balances[from] -= amount;
        _balances[to] += amount;
        _allowances[from][msg.sender] -= amount;

        emit Transfer(from, to, amount);
        return true;
    }
}

Important Notes

Always check for zero address to avoid sending tokens to nowhere.

Events like Transfer and Approval help wallets and apps track token movements.

Decimals define how divisible your token is; 18 is common like Ether.

Summary

ERC-20 is a standard for tokens on Ethereum.

It defines functions to check balances, transfer tokens, and approve spending.

Following ERC-20 makes your token work with many wallets and exchanges.