[Ethereum] how to loop through a mapping of address to struct

solidity

I have a mapping where the key is the artist name, the value is msg.sender address. In a function, I want to check if the parameter username has already existed in the mapping keys, if yes, i will throw

How do I loop through a mapping of value keys to check and compare with input parameter?

mapping(bytes32 => address) public reserved_names;

function create_artist(bytes32 username, string ipfs) {

   //todo throw exception if artists username already exists

   reserved_names[username] = msg.sender;

Best Answer

assert(reserved_names[username] == 0x0);

Related Solutions

Solidity – VM Exception: Invalid JUMP When Calling a Second Function

You need to add the constant keyword to the test() function like:

pragma solidity ^0.4.0;
contract Test {
    mapping (address => uint256) weismap;

    function bet(uint vote) payable returns (uint256 weis) {
        if (msg.value==0) 
            throw;
        weismap[msg.sender]= msg.value;
        return  weismap[msg.sender];
    }

    function test() constant returns (uint myVote)  {
        return 1;
    }
}

Calling bet(...) with the value 2. Note that I'm sending 2 ethers as well with the transaction:

Now I call test() AND I've left the value 2. This call to test() fails as the constant function is being called as a transaction, not a read of the values off the blockchain:

If I call test() AND I've set value to blank, this call to test() succeeds as the constant function is being called as a read of the values off the blockchain:

Solidity – Handling Unimplemented Functions in Contracts

The problem is that totalSupply() implementation is missing. Seems like autogenerated getters do not count. So you need to explicitly create the function.

contract StandardToken is Token {
    uint256 _totalSupply;

    function totalSupply() constant returns (uint256 totalSupply) {
        totalSupply = _totalSupply;
    }
}

Best Answer

Related Solutions

Solidity – VM Exception: Invalid JUMP When Calling a Second Function

Solidity – Handling Unimplemented Functions in Contracts

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