[Ethereum] Smart contract erc20 code snippet to prevent buyer token transfers

erc-20go-ethereumsmart-locktokens

I´m going to start a token pre-sale and I want to be able to send the tokens to the buyer but prevent the buyer to send tokens to another wallet.

I tried the following in my ERC20 smart contract but It actually prevent myself, the contract creator, to transfer tokens. I need to be able to send tokens to buyers and prevent buyers to transfer tokens till certain time in the future.

here is the test smart contract contract: https://etherscan.io/address/0x5783f4e4a1bec72f41f246c50ba3d06265d984a6#code

function transfer( address _to, uint _value) public {
require( now > 1514764800 );
/* Rest of Function */
}

Best Answer

You can do this.

modifier notPaused {
    require(now > 1514764800  || msg.sender == owner);
    _;
}

function transfer(address to, uint256 amount) public notPaused returns(bool) {
    //rest of function
}

Related Solutions

Solidity – Handling Unimplemented Functions in Contracts

The problem is that totalSupply() implementation is missing. Seems like autogenerated getters do not count. So you need to explicitly create the function.

contract StandardToken is Token {
    uint256 _totalSupply;

    function totalSupply() constant returns (uint256 totalSupply) {
        totalSupply = _totalSupply;
    }
}

Solidity – Can a Smart Contract Identify Which Address Sent an ERC20 Token?

Upon a successful transfer of an ERC20 token, an event containing the parties' addresses and the value amount transfered is emitted. The Transfer event looks like:

event Transfer(address indexed _from, address indexed _to, uint _value);

Your contract can listen to the token contract for Transfer events where your contract is the _to parameter - you can do this off-chain using the web3 api watch event.

You may find these related questions helpful:

Detect token transaction to a contract

Call a smart contract payable function sending erc20 token

Best Answer

Related Solutions

Solidity – Handling Unimplemented Functions in Contracts

Solidity – Can a Smart Contract Identify Which Address Sent an ERC20 Token?

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