how to read smart contract A's data from other smart contract B in ethereum?

Question

Currently, we can read the contract A data with the help of getters functions defined in contract A.
But I want to do something like contract A puts some data in ethereum blockchain but do not define the getters or other functions to access it. And then using another smart contract B, I want to access smart contract B data directly from blocks fo ethereum blockchain.

Answer 1

A smart contract can only access its own storage, you cannot read the storage of another contract directly, with Solidity. If you cannot make the variables public, or make a getter for the variables, you can use something like Web3.js or Ethers.js to read the contract storage, and send that data to your contract, e.g.:

import { JsonRpcProvider } from 'ethers';

const provider = new JsonRpcProvider('https://<URL of your node>'); // or use Infura, Etherscan, ...
const data = await provider.getStorageAt("<contract address>", <storage slot>);

You can read more about how the storage works here: https://solidity.readthedocs.io/en/v0.7.0/internals/layout_in_storage.html