How to send etherenum to msg.sender in solidity 0.5.0

Question

mapping(uint => Product) public products;

struct Product {

    uint id;
    string name;
    uint price;
    address payable owner;
    bool purchased;   
}

function purchaseProduct(unit _id) public payable {

    Product memory _product = products[_id];
    address payable _seller = _product.owner;
    address payable _buyer = msg.sender;
}

address(_seller).transfer(msg.value) works good. But msg.sender.transfer(msg.value) and address(_buyer).transfer(msg.value) doesn't work.

please help me to fix this issue.

Answer 1

In this block (added line number), msg.value is the amount of ether transferred to the contract when calling function.

At line 1, it has already transferred all the ether to _seller. Line 2 and 3 will fail because there is no more ether left.

1    address(_seller).transfer(msg.value);
2    address(_buyer).transfer(msg.value);
3    msg.sender.transfer(msg.value);  

Example: I call purchaseProduct() function with value of 1 ether.

1. address(_seller).transfer(msg.value) transfers 1 ether to _seller .
2. address(_buyer).transfer(msg.value) transfers 1 ether to _seller .
3. msg.sender.transfer(msg.value) transfers 1 ether to _seller .

It fails because there's only 1 ether.