erc20 example

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    lucycodes42

    Solidity Code Snippets

    Shortcut: erc20

    // https://eips.ethereum.org/EIPS/eip-20
    // SPDX-License-Identifier: MIT
    pragma solidity >=0.5.0 <0.8.0;
    
    interface Token {
    
        /// @param _owner The address from which the balance will be retrieved
        /// @return balance the balance
        function balanceOf(address _owner) external view 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 success Whether the transfer was successful or not
        function transfer(address _to, uint256 _value)  external 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 success Whether the transfer was successful or not
        function transferFrom(address _from, address _to, uint256 _value) external 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 success Whether the approval was successful or not
        function approve(address _spender  , uint256 _value) external 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 remaining Amount of remaining tokens allowed to spent
        function allowance(address _owner, address _spender) external view returns (uint256 remaining);
    
        event Transfer(address indexed _from, address indexed _to, uint256 _value);
        event Approval(address indexed _owner, address indexed _spender, uint256 _value);
    }
    
    contract Standard_Token is Token {
        uint256 constant private MAX_UINT256 = 2**256 - 1;
        mapping (address => uint256) public balances;
        mapping (address => mapping (address => uint256)) public allowed;
        uint256 public totalSupply;
        /*
        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.
        string public symbol;                 //An identifier: eg SBX
    
        constructor(uint256 _initialAmount, string memory _tokenName, uint8 _decimalUnits, string  memory _tokenSymbol) {
            balances[msg.sender] = _initialAmount;               // Give the creator all initial tokens
            totalSupply = _initialAmount;                        // Update total supply
            name = _tokenName;                                   // Set the name for display purposes
            decimals = _decimalUnits;                            // Amount of decimals for display purposes
            symbol = _tokenSymbol;                               // Set the symbol for display purposes
        }
    
        function transfer(address _to, uint256 _value) public override returns (bool success) {
            require(balances[msg.sender] >= _value, "token balance is lower than the value requested");
            balances[msg.sender] -= _value;
            balances[_to] += _value;
            emit Transfer(msg.sender, _to, _value); //solhint-disable-line indent, no-unused-vars
            return true;
        }
    
        function transferFrom(address _from, address _to, uint256 _value) public override returns (bool success) {
            uint256 allowance = allowed[_from][msg.sender];
            require(balances[_from] >= _value && allowance >= _value, "token balance or allowance is lower than amount requested");
            balances[_to] += _value;
            balances[_from] -= _value;
            if (allowance < MAX_UINT256) {
                allowed[_from][msg.sender] -= _value;
            }
            emit Transfer(_from, _to, _value); //solhint-disable-line indent, no-unused-vars
            return true;
        }
    
        function balanceOf(address _owner) public override view returns (uint256 balance) {
            return balances[_owner];
        }
    
        function approve(address _spender, uint256 _value) public override returns (bool success) {
            allowed[msg.sender][_spender] = _value;
            emit Approval(msg.sender, _spender, _value); //solhint-disable-line indent, no-unused-vars
            return true;
        }
    
        function allowance(address _owner, address _spender) public override view returns (uint256 remaining) {
            return allowed[_owner][_spender];
        }
    }
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