Smart contract erc20 code snippet to prevent buyer token transfers

Question

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 */ }

Answer 1

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
}

Answer 2

//this is where you declare the identifier owner

address owner;

//whith this modifier, only you can call the transfer function 
//when now <= 1514764800.

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

//the identifier owner is initialized once the contract is deployed and 
//set to the address of the message sender. Note that this should be in 
//the constructor of the contract, which is always the function with the
//same name as the contract.

function ERC20Token() {
    owner  = msg.sender;
    //rest of constructor
}

//by adding notPaused here, the function will only successfully execute when
//A: you the owner call the function before or after the block 1514764800 or
//B: when anyone else calls the the function after the block 1514764800

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