How do ICOs with token price linked to fiat currency prices work?

Question

So when I see most Crowdsale contracts the price is set to x ETH and you receive the tokens based on that, if ETH price is down you get more tokens/$ and when ETH price is up, you get less/$. That's just the volatility of crypto. But some tokens are linked to fiat prices directly. $1 gets 1 token so if I send 1 ETH I get however many tokens are determined by the price of ETH.

How is this accomplished?

Answer 1

Usually, they lock the price just before starting the crowdsale. They set it to a certain value, and it will stay like that during the entire crowdsale.

It can be something like that :

function startCrowdsale(uint _price) {
    crowdsale_started = true;
    price = _price;
    //more code
}

Another way, but more costly, is the use of an oracle.

Answer 2

there is one more way they do it. they calculate the price of ether at the time they receive your payments or they just look the price of ether at the end of ico and all the prices are current value in the market

Answer 3

There used to be several ways to achieve something similar but each method has its inconveniences:

• Use an oracle to determine exchange price. You need to trust the oracle will not be compromised. It might be expensive to call the oracle in each transaction.
• Set prices using a bot. You need to trust the team will not manipulate the prices. Prices have to have a threshold so they are updated when it varies above 2% for example.