USD Coin Balance Check By Web3

Question

Now I am getting trouble on checking the USDC balance in my wallet address using web3.

USDC is also said that it is ERC20 token, but when I checked the token contract

0xa0b86991c6218b36c1d19d4a2e9eb0ce3606eb48

This doesn't contain the erc20 standard. So I guess I can't use the traditional token balance checking way in this coin. Also I tried in traditional way, but it never work. How can I check the USDC balance / and create transfer transaction from one address to another using Web3?

score 5 · Accepted Answer · answered May 08 '19 at 09:49

5

This is proxy contract, which means that it delegates actual work to another contract, probably to this one: 0x0882477e7895bdc5cea7cb1552ed914ab157fe56, which in turn is ERC-20 compliant. Proxy contract allows its administrator to change address of the contract actual work is delegated to, effectively changing smart contract logic. Proxy contracts like this one are implemented via DELEGATECALL opcode that executes code of another contract on behalf of this contract, i.e. called code has access to the storage and balance of calling contract.

answered May 08 '19 at 09:49

Mikhail Vladimirov

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Could you tell me how to use the proxy contract, and DELEGATECALL? – Francesco Rossi May 08 '19 at 10:38
This depends on what do you want to use it for, and probably is it subject for another question. Check this answer: https://ethereum.stackexchange.com/questions/2404/upgradeable-smart-contracts/58178#58178 – Mikhail Vladimirov May 08 '19 at 10:45
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how did you find the 0x088..fe56 addr? – c-o-d Aug 23 '20 at 07:07
can someone please explain how to decode the implementation contract address and its abi for such proxied contract so that ? – cryptoKTM Sep 18 '20 at 16:35

score 1 · Answer 2 · answered Sep 19 '20 at 08:48

This doesn't contain the erc20 standard.

Thats true if you check the abi for this contract 0xa0b86991c6218b36c1d19d4a2e9eb0ce3606eb48 you wont find erc standard methods and Mikko and Mikhail explained why what is happening behind,

If you want to check balance for usdc you can use use abi for any other erc20 standard like DAI and the contract address for usdc this will work perfectly fine and the reason why dai abi work for usdc is the default ERC20 functions, events and variables are the same in DAI and USDC tokens, one ABI is sufficient for both cases. Check here for better explanation

score 0 · Answer 3 · answered May 08 '19 at 09:31

This doesn't contain the erc20 standard.

Not sure what you mean here.

Solidity contracts do not have a way to explicitly tell if a contract supports some interface or not. The only way to ensure interface compatibility is through so called duck typing - test that balanceOf method returns values and contract does not revert when the method is called.

You need to follow the "social contract" and as by the authors instructions assume that the balance method exist.

What comes to actual checking balance and making a token transaction in front end JavaScript, there are plenty of generic tutorials available for ERC-20 tokens. Furthermore you should find answers on this StackExchange as well.

USD Coin Balance Check By Web3

3 Answers3