Remix IDE测试Solidity合约遇Gas估算错误，Buy功能无法执行求助

Hey there, let's walk through why your Buy function is throwing that frustrating gas estimation error—this is a super common issue when building payment-focused smart contracts, so let's break down the most likely causes:

• Product validity checks failing
  Chances are your Buy function has require statements to verify the product exists or is still available, and one of those is failing. For example, if you forgot to mark products as "existing" when calling add_product, or the product was already purchased, the require will trigger a transaction rollback, which Remix flags as a gas estimation error. Double-check code like:

  require(products[productId].exists == true, "Product doesn't exist");
  require(products[productId].isAvailable == true, "Product sold out");
  

  Make sure these conditions are actually met when you try to call Buy.

• Incorrect ETH amount sent
  Your Buy function almost certainly expects the caller to send exactly the product's price via msg.value. If you don't fill in the "Value" field in Remix (or fill in the wrong amount), the require(msg.value == products[productId].price, "Wrong ETH amount") check will fail, causing the transaction to revert. Always confirm you're sending the exact price listed for the product you're trying to buy.

• ETH transfer to seller failing
  When sending ETH to the product's seller, issues here can trigger a revert. Common problems include:

  • The seller address isn't marked as payable (if it's a contract or a user address stored in your product struct, make sure it's declared as address payable).
  • Using transfer() which has a 2300 gas limit—if the seller's address is a contract with a fallback function that needs more than 2300 gas, transfer() will fail. Try using call{value: msg.value}("") instead, and make sure to check the return value:

    (bool success, ) = payable(product.seller).call{value: msg.value}("");
    require(success, "Transfer to seller failed");
    

• Overflow/underflow issues (pre-Solidity 0.8.0)
  If you're using a Solidity version older than 0.8.0, automatic overflow/underflow checks aren't enabled. If your Buy function modifies values like inventory count and causes an overflow (e.g., subtracting 1 from 0), this will silently corrupt state in older versions—but in 0.8.0+, it triggers an immediate revert, which shows up as a gas estimation error. Upgrade to 0.8.0+ if you haven't already, or add SafeMath libraries for older versions.

• Remix environment glitches
  Sometimes the issue isn't your code at all. Try these quick fixes:

  • Re-deploy your contract from scratch (sometimes cached state in Remix can cause weird behavior).
  • Switch the Remix VM environment (e.g., from "Remix VM (London)" to "Remix VM (Berlin)") and test again.
  • Make sure you're interacting with the correct deployed contract instance (check the address in the "Deployed Contracts" section).

• Incorrect function modifiers or permissions
  If you accidentally added a modifier like onlyOwner to the Buy function, regular users (including your test account) won't be able to call it, triggering a revert. Double-check that your Buy function is declared as external payable without unnecessary restrictions.

内容的提问来源于stack exchange，提问作者Traoré Moussa