I have a problem using a transfer function in my smart contract solidity 0.4.16

Question

So basically, I want a transfer function of ERC20 tokens on 0.4.16, but I want to make it so that you can specify which token you want to transfer to another address, but everytime I try to send tokens, there's an error, I think it's because the "msg.sender" has to approve the tokens, but idk, this is the code, if you want to review it:

pragma solidity 0.4.16;

interface ERC20 {
    function transfer(address _to, uint256 _value) public returns (bool);
}

contract TokenTransfer {
    function transferToken(address _tokenAddress, address _to, uint256 _value) public returns (bool) {
        // Create an instance of the ERC20 token contract
        ERC20 token = ERC20(_tokenAddress);

        // Transfer the specified amount of tokens to the specified address
        return token.transfer(_to, _value);
    }
}

Answer 1

transfer() would transfer tokens that are already in your contract to _to, and is gonna fail if your contract doesn't have the required balance. If you want to take tokens from the user calling transferToken(), you'll need to use transferFrom(), and in that case you're going to need approval, yes.