How to encode string as bytes array?

Question

A similar question has been asked but using web3 in java, however, I would like to encode a string to bytes[] in solidity itself.

Answer 1

Supposing your string comes from an external source (someone outside your contract calls the function with such string as a parameter) you can cast it to bytes and then slice the bytes into an array. Something like this.

contract Cast {

    bytes [] public arr;

    function convertExternalString(string calldata str) external{
        bytes calldata bts =bytes(str);
        for(uint i; i<bts.length; i++){
            arr.push(bts[i:i+1]);
        }
    }

}

Now, if your string is stored on the contract you can also convert it but would have to change the visibility of the function convertExternalString to public and then call it with a this.. The next code works.

contract Cast {

    bytes [] public arr;
    string public st = "Hello";

    function convertInternalString() public {
        this.convertExternalString(st);
    }

    function convertExternalString(string calldata str) public {
        bytes calldata bts =bytes(str);
        for(uint i; i<bts.length; i++){
            arr.push(bts[i:i+1]);
        }
    }

}

Note that calldata slicing is only available for solidity 0.6.0 and above.