Can't return string when function not pure? [duplicate]

Question

This question already has an answer here:

• What is the difference between a transaction and a call? 2 answers

See the below contract function of which return the string (Tested in Remix.org):

pragma solidity >=0.4.22 <0.6.0;
contract HelloWorld {
    function get() pure public returns (string memory){
        return "Hello Solidity";
    }
}

While in the following contract, I can't get the returned string.

pragma solidity >=0.4.22 <0.6.0;
contract HelloWorld {
    uint num;
    function get(uint val) public returns (string memory){
        num = val;
        return "Hello Solidity";
    }
}

Why? And how can I get returned string from not pure function ?

Answer 1

Web3 API does not allow obtaining return values of functions executed on-chain, i.e. in mined transactions. Though, in case other contract will execute your functions, it will get return value.

This is because values returned by transactions are not stored in blocks, so in order to obtain such value one will need to replay the transaction. You may replay the transaction via contract.methods.method.call(...).