How to set msg.value in solidity function call

Question

If I have a function:

contract one {
      function buyTokens(address _beneficiary) public payable {
        require(msg.value == 1 ether);
       // do something...
      }
}

How do I call that function and also pay ether using solidity?

contract two {
    ...
    function doBuy(uint _amount) public {
       one.buyTokens(msg.sender, _amount);
    }

How do I set msg.value as part of the function call?

score 10 · Accepted Answer · edited Oct 25 '21 at 15:44

10

If I understand your question correctly, you want to make a call from one contract to another contract's payable function and make an ETH transfer with it, if so you can do it with:

address.function{ value: amount }(arg1, arg2, arg3)

In your case:

function doBuy(uint _amount) public {
   contractOfTheBuyTokensFunction.buyTokens{ value: _amount }(msg.sender);
}

edited Oct 25 '21 at 15:44

caffeinum

142
7

answered Oct 10 '18 at 00:43

Nikolay Deshev

304
1
6

4

address.function.value(amount)(arg1, arg2, arg3) is now deprecated. Use address.function{value:amount}(arg1, arg2, arg3) instead. – Girish Thimmegowda May 24 '20 at 18:38

score 3 · Answer 2 · answered Oct 10 '18 at 00:34

Things like msg.sender and msg.value will stay constant for a single transaction, no matter how many different functions are called throughout the process. So you do not need to pass these values around, they are always available by default in each function's context.

So in this case, where you have one function which simply calls another, you could just do:

pragma solidity ^0.4.24;

contract test{

    mapping(address => bool) public buyers;

    function doBuy() public payable {
       buyTokens();
    }

    function buyTokens() private returns(address){
      require(msg.value == 1 ether);
      buyers[msg.sender] = true;
    }
}

A few things to note here, which is different than your code snippet.

You need to make doBuy() payable since it is the entry point for the second function, and ultimately it is the function that users call and send the Ether to.
You do not need to make buyTokens() payable, since it is not directly called by the user.
I made buyTokens() private because I suspect that the user is supposed to call doBuy() and not buyTokens()
You will see that buyTokens() has access to both msg.value and msg.sender even though it is never directly called or passed those values.

I meant that doBuy is in a different contract. updated the question to be more clear on that point. — Mark Irvine, Oct 10 '18 at 09:26

How to set msg.value in solidity function call

2 Answers2