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ERC20 Token Standard #610
ERC20 Token Standard #610
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## Preamble | ||
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EIP: 20 | ||
Title: ERC-20 Token Standard | ||
Author: Fabian Vogelsteller <fabian@ethereum.org>, Vitalik Buterin <vitalik.buterin@ethereum.org> | ||
Type: Standard | ||
Category: ERC | ||
Status: Accepted | ||
Created: 2015-11-19 | ||
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## Simple Summary | ||
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A standard interface for tokens. | ||
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## Abstract | ||
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The following standard allows for the implementation of a standard API for tokens within smart contracts. | ||
This standard provides basic functionality to transfer tokens, as well as allow tokens to be approved so they can be spent by another on-chain third party. | ||
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## Motivation | ||
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A standard interface allows any tokens on Ethereum to be re-used by other applications: from wallets to decentralized exchanges. | ||
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## Specification | ||
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## Token | ||
### Methods | ||
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**NOTE**: Callers MUST handle `false` from `returns (bool success)`. Callers MUST NOT assume that `false` is never returned! | ||
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#### name | ||
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Returns the name of the token - e.g. `"MyToken"` | ||
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``` js | ||
function name() constant returns (string name) | ||
``` | ||
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#### symbol | ||
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Returns the symbol of the token. E.g. "MYT" | ||
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``` js | ||
function symbol() constant returns (string symbol) | ||
``` | ||
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#### decimals | ||
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Returns the number of decimals the token uses - e.g. `8`, means to divide the token amount by `100000000` to get its user representation. | ||
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``` js | ||
function decimals() constant returns (uint8 decimals) | ||
``` | ||
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#### totalSupply | ||
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Returns the total token supply. | ||
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``` js | ||
function totalSupply() constant returns (uint256 totalSupply) | ||
``` | ||
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#### balanceOf | ||
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Returns the account balance of another account with address `_owner`. | ||
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``` js | ||
function balanceOf(address _owner) constant returns (uint256 balance) | ||
``` | ||
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#### transfer | ||
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Transfers `_value` amount of tokens to address `_to`, and MUST fire the `Transfer` event. | ||
The function SHOULD `throw` if the `_from` account balance has not enough tokens to spend. | ||
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*Note* Transfers of 0 values MUST be treated as normal transfers and fire the `Transfer` event. | ||
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``` js | ||
function transfer(address _to, uint256 _value) returns (bool success) | ||
``` | ||
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#### transferFrom | ||
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Transfers `_value` amount of tokens from address `_from` to address `_to`, and MUST fire the `Transfer` event. | ||
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There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. Please add:
There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. I believe that when amount == 0 it should return true, but no Transfer event should be emmited because there is no transfer. There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. Valid point that 0 tokens are transferred, but most current implementations fire the event when |
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The `transferFrom` method is used for a withdraw workflow, allowing contracts to transfer tokens on your behalf. | ||
This can be used for example to allow a contract to transfer tokens on your behalf and/or to charge fees in sub-currencies. | ||
The function SHOULD `throw` unless the `_from` account has deliberately authorized the sender of the message via some mechanism. | ||
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*Note* Transfers of 0 values MUST be treated as normal transfers and fire the `Transfer` event. | ||
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``` js | ||
function transferFrom(address _from, address _to, uint256 _value) returns (bool success) | ||
``` | ||
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#### approve | ||
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Allows `_spender` to withdraw from your account multiple times, up to the `_value` amount. If this function is called again it overwrites the current allowance with `_value`. | ||
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**NOTE**: To prevent attack vectors like the one [described here](https://docs.google.com/document/d/1YLPtQxZu1UAvO9cZ1O2RPXBbT0mooh4DYKjA_jp-RLM/) and discussed [here](https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729), | ||
make sure to force users to set the allowance to `0` before setting it to another value for the same spender. | ||
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``` js | ||
function approve(address _spender, uint256 _value) returns (bool success) | ||
``` | ||
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#### allowance | ||
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Returns the amount which `_spender` is still allowed to withdraw from `_owner`. | ||
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``` js | ||
function allowance(address _owner, address _spender) constant returns (uint256 remaining) | ||
``` | ||
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### Events | ||
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#### Transfer | ||
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MUST trigger when tokens are transferred. | ||
There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. Suggest changing this to
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``` js | ||
event Transfer(address indexed _from, address indexed _to, uint256 _value) | ||
``` | ||
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#### Approval | ||
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MUST trigger when `approve(address _spender, uint256 _value)` is called. | ||
There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. Suggest changing to:
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``` js | ||
event Approval(address indexed _owner, address indexed _spender, uint256 _value) | ||
``` | ||
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## Implementation | ||
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There are already plenty of ERC20-compliant tokens deployed on the Ethereum network. | ||
Different implementations have been written by various teams that have different trade-offs: from gas saving to improved security. | ||
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#### Example implementations are available at | ||
- https://github.com/OpenZeppelin/zeppelin-solidity/blob/master/contracts/token/StandardToken.sol | ||
- https://github.com/ConsenSys/Tokens/blob/master/Token_Contracts/contracts/StandardToken.sol | ||
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There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. https://github.com/Giveth/minime/blob/master/contracts/MiniMeToken.sol There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. :-D!!! There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. I would also like to see the MiniMeToken added to this list. Maintaining historical balance data is key for a number of token use cases. |
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#### Implementation of adding the force to 0 before calling "approve" again: | ||
- https://github.com/Giveth/minime/blob/master/contracts/MiniMeToken.sol | ||
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## Copyright | ||
Copyright and related rights waived via [CC0](https://creativecommons.org/publicdomain/zero/1.0/). |
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How about adding: