Solidity – How to Pass Parameters to Remix

remixsolidity

I am trying to implement the contract below in REMIX.

If I try to pass parameters to appendTags as "tag1", I get an error as Error:

invalid bytes32 value (arg="", type="string", value="tag1")

How can I pass parameters to the function appendTags in REMIX ?

contract Post{

struct tags{
bytes32[] tagged; 
}

mapping(address => tags) adminTags;

function appendTags(address addrs, bytes32 tag) public { 
 adminTags[addrs].tagged.push(tag); 
} 

function getTagsofAdmin(address addrs) public view returns(bytes32[]){ 
return adminTags[addrs].tagged; 
}

}

Best Answer

As the Solidity code specifies, you need to pass a bytes32 value as argument, not an ascii-encoded word. This is an hexadecimal-encoded value, so as a rule of thumb it should start with 0x.

Before passing your argument, you thus need to hex-encode it using for example one of web3 util's functions:

> web3.utils.fromAscii('tag1')
'0x74616731'

You can pass this hexadecimal value as an argument in the Remix console. Later when you call getTagsOfAdmin you'll simply need to apply the reverse transformation:

> web3.utils.toAscii('0x74616731')
'tag1'

Despite this added complexity, bytes32 prove a good alternative against strings because they have fixed length and hence require way less storage costs. Hope it helps!

PS: note that the above command-line examples use web3 v1.

Related Solutions

Solidity Mapping – How to Return a Mapping Type

You need to break the interface down into smaller chunks. In practice, you'll want to extend the internal storage pattern a little, I think.

Iterable mapping comes to mind. You keep lists of keys to mappings in arrays. Something like this:

  struct VoterStruct {
    address voterAddress;
    uint256 tokensBought;
    mapping (bytes32 => uint256) tokensUsed;
    bytes32[] tokenIndex; // a list of mapping keys that exist for the voter
  }

  mapping (address => VoterStruct) public voterStructs;

Then you can expose functions that allow iterating over lists while the contract returns one set of values at a time. Very sketchy to inspire some ideas:

// client can discover how may tokens are in the list for one voter
function getVoterTokenCount(address voter) returns(uint tokenCount) {
    return voterStructs[voter].tokenIndex.length;}

// client can discover the tokenId for a voter in a given row
function getVoterTokenAtIndex(address voter, uint index) returns(bytes32 tokenId) {
    return voterStructs[voter].tokenIndex[index];}

// client can discover token used by voter and tokenId
function getVoterTokenUsed(address voter, bytes32 tokenId) returns(uint tokensUsed) {
    return voterStructs[voter].tokensUsed[tokenId];}

// append keys to the list as you go
function insertVoterToken(address voter, bytes32 tokenId) returns(bool success) {
    voterStructs[voter].tokenIndex.push(tokenId);
    return true;}

Hope I didn't flub the syntax. It might be possible to sketch out the contract a little more. Would need a general description of what it's going to do. When I use this pattern, I always add some rules to ensure there are no duplicate keys, and so on.

Anyway, possibly the hints will inspire some ideas.

Hope it helps.

Solidity – Error When Encoding Arguments to Call a Function with Bytes32 Type Parameters

You need to convert the value in hex to be passed. neo is 0x6e656f in hex. If you try to pass '0x6e656f' it will work (don't forget the quote).

Best Answer

Related Solutions

Solidity Mapping – How to Return a Mapping Type

Solidity – Error When Encoding Arguments to Call a Function with Bytes32 Type Parameters

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