Difference between revisions of "How to create your own Ethereum ERC20 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;
   }

}