mirror of https://github.com/status-im/EIPs.git
Move eip-20-token-standard.md to eip-20.md
To prevent dangling links, I left a notice in eip-20-token-standard.md
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Yoichi Hirai
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## Preamble
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EIP: 20
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Title: ERC-20 Token Standard
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Author: Fabian Vogelsteller <fabian@ethereum.org>, Vitalik Buterin <vitalik.buterin@ethereum.org>
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Type: Standard
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Category: ERC
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Status: Accepted
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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.
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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
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### 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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OPTIONAL - This method can be used to improve usability,
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but interfaces and other contracts MUST NOT expect these values to be present.
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``` js
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function name() constant returns (string name)
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```
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#### symbol
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Returns the symbol of the token. E.g. "HIX".
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OPTIONAL - This method can be used to improve usability,
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but interfaces and other contracts MUST NOT expect these values to be present.
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``` js
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function symbol() constant returns (string symbol)
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```
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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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OPTIONAL - This method can be used to improve usability,
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but interfaces and other contracts MUST NOT expect these values to be present.
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``` js
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function decimals() constant returns (uint8 decimals)
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```
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#### totalSupply
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Returns the total token supply.
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``` js
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function totalSupply() constant returns (uint256 totalSupply)
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```
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#### balanceOf
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Returns the account balance of another account with address `_owner`.
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``` js
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function balanceOf(address _owner) constant returns (uint256 balance)
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```
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#### transfer
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Transfers `_value` amount of tokens to address `_to`, and MUST fire the `Transfer` event.
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The function SHOULD `throw` if the `_from` account balance does not have 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
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function transfer(address _to, uint256 _value) returns (bool success)
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```
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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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The `transferFrom` method is used for a withdraw workflow, allowing contracts to transfer tokens on your behalf.
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This can be used for example to allow a contract to transfer tokens on your behalf and/or to charge fees in sub-currencies.
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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
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function transferFrom(address _from, address _to, uint256 _value) returns (bool success)
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```
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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),
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clients SHOULD make sure to create user interfaces in such a way that they set the allowance first to `0` before setting it to another value for the same spender.
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THOUGH The contract itself shouldn't enforce it, to allow backwards compatibility with contracts deployed before
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``` js
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function approve(address _spender, uint256 _value) returns (bool success)
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```
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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
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function allowance(address _owner, address _spender) constant returns (uint256 remaining)
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```
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### Events
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#### Transfer
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MUST trigger when tokens are transferred, including zero value transfers.
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A token contract which creates new tokens SHOULD trigger a Transfer event with the `_from` address set to `0x0` when tokens are created.
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``` js
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event Transfer(address indexed _from, address indexed _to, uint256 _value)
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```
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#### Approval
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MUST trigger on any successful call to `approve(address _spender, uint256 _value)`.
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``` js
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event Approval(address indexed _owner, address indexed _spender, uint256 _value)
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```
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## Implementation
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There are already plenty of ERC20-compliant tokens deployed on the Ethereum network.
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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
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- https://github.com/OpenZeppelin/zeppelin-solidity/blob/master/contracts/token/ERC20/StandardToken.sol
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- https://github.com/ConsenSys/Tokens/blob/master/contracts/eip20/EIP20.sol
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#### Implementation of adding the force to 0 before calling "approve" again:
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- https://github.com/Giveth/minime/blob/master/contracts/MiniMeToken.sol
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## History
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Historical links releated to this standard:
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- Orginial proposal from Vitalik Buterin: https://github.com/ethereum/wiki/wiki/Standardized_Contract_APIs/499c882f3ec123537fc2fccd57eaa29e6032fe4a
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- Reddit discussion: https://www.reddit.com/r/ethereum/comments/3n8fkn/lets_talk_about_the_coin_standard/
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- Original Issue #20: https://github.com/ethereum/EIPs/issues/20
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## Copyright
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Copyright and related rights waived via [CC0](https://creativecommons.org/publicdomain/zero/1.0/).
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Moved to [eip-20.md](./eip-20.md).
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@ -0,0 +1,196 @@
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## Preamble
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EIP: 20
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Title: ERC-20 Token Standard
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Author: Fabian Vogelsteller <fabian@ethereum.org>, Vitalik Buterin <vitalik.buterin@ethereum.org>
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Type: Standard
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Category: ERC
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Status: Accepted
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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.
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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
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### 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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OPTIONAL - This method can be used to improve usability,
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but interfaces and other contracts MUST NOT expect these values to be present.
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``` js
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function name() constant returns (string name)
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```
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#### symbol
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Returns the symbol of the token. E.g. "HIX".
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OPTIONAL - This method can be used to improve usability,
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but interfaces and other contracts MUST NOT expect these values to be present.
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``` js
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function symbol() constant returns (string symbol)
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```
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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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OPTIONAL - This method can be used to improve usability,
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but interfaces and other contracts MUST NOT expect these values to be present.
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``` js
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function decimals() constant returns (uint8 decimals)
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```
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#### totalSupply
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Returns the total token supply.
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``` js
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function totalSupply() constant returns (uint256 totalSupply)
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```
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#### balanceOf
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Returns the account balance of another account with address `_owner`.
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``` js
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function balanceOf(address _owner) constant returns (uint256 balance)
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```
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#### transfer
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Transfers `_value` amount of tokens to address `_to`, and MUST fire the `Transfer` event.
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The function SHOULD `throw` if the `_from` account balance does not have 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
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function transfer(address _to, uint256 _value) returns (bool success)
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```
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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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The `transferFrom` method is used for a withdraw workflow, allowing contracts to transfer tokens on your behalf.
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This can be used for example to allow a contract to transfer tokens on your behalf and/or to charge fees in sub-currencies.
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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
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function transferFrom(address _from, address _to, uint256 _value) returns (bool success)
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```
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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),
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clients SHOULD make sure to create user interfaces in such a way that they set the allowance first to `0` before setting it to another value for the same spender.
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THOUGH The contract itself shouldn't enforce it, to allow backwards compatibility with contracts deployed before
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``` js
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function approve(address _spender, uint256 _value) returns (bool success)
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```
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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
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function allowance(address _owner, address _spender) constant returns (uint256 remaining)
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```
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### Events
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#### Transfer
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MUST trigger when tokens are transferred, including zero value transfers.
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A token contract which creates new tokens SHOULD trigger a Transfer event with the `_from` address set to `0x0` when tokens are created.
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``` js
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event Transfer(address indexed _from, address indexed _to, uint256 _value)
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```
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#### Approval
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MUST trigger on any successful call to `approve(address _spender, uint256 _value)`.
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``` js
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event Approval(address indexed _owner, address indexed _spender, uint256 _value)
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```
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## Implementation
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There are already plenty of ERC20-compliant tokens deployed on the Ethereum network.
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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
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- https://github.com/OpenZeppelin/zeppelin-solidity/blob/master/contracts/token/ERC20/StandardToken.sol
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- https://github.com/ConsenSys/Tokens/blob/master/contracts/eip20/EIP20.sol
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#### Implementation of adding the force to 0 before calling "approve" again:
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- https://github.com/Giveth/minime/blob/master/contracts/MiniMeToken.sol
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## History
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Historical links releated to this standard:
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- Orginial proposal from Vitalik Buterin: https://github.com/ethereum/wiki/wiki/Standardized_Contract_APIs/499c882f3ec123537fc2fccd57eaa29e6032fe4a
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- Reddit discussion: https://www.reddit.com/r/ethereum/comments/3n8fkn/lets_talk_about_the_coin_standard/
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- Original Issue #20: https://github.com/ethereum/EIPs/issues/20
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## Copyright
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||||
Copyright and related rights waived via [CC0](https://creativecommons.org/publicdomain/zero/1.0/).
|
||||
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