Mapping to bool not default to false

Question

Consider this voting contract

contract Voting {
  mapping (bytes32 => uint8) public votesReceived;
  mapping (bytes32 => bool) public candidateList;
  function Voting(bytes32[] candidateNames) {
    for(uint i = 0; i < candidateNames.length; i++) {
      candidateList[candidateNames[i]] = true;
    }
  }
  function totalVotesFor(bytes32 candidate) returns (uint8) {
    require(validCandidate(candidate) == true);
    return votesReceived[candidate];
  }
  function voteForCandidate(bytes32 candidate) {
    require(validCandidate(candidate) == true);
    votesReceived[candidate] += 1;
  }
  function validCandidate(bytes32 candidate) returns (bool) {
    return candidateList[candidate];
  }
}

if I call validCandidate with a valid name (ie. a name included in the array passed to the constructor), it works. But for invalid names, I got a invalid opcode exception. I thought that maps had 0/false by default, is it not the case?

Answer 1

In solidity, the default value is 'zero', for uint is 0, bool is false. If you find a element that is included this mapping by key, so it returns default value.

In your contract, there is two unreasonable use, a function that doesn't modify status， you should declare a constant function.

contract Voting {

  mapping (bytes32 => uint8) public votesReceived;
  mapping (bytes32 => bool) public candidateList;

  function Voting(bytes32[] candidateNames) {
    for(uint i = 0; i < candidateNames.length; i++) {
      candidateList[candidateNames[i]] = true;
    }
  }

  function totalVotesFor(bytes32 candidate) constant returns (uint8) {
    require(validCandidate(candidate));
    return votesReceived[candidate];
  }

  function voteForCandidate(bytes32 candidate) {
    require(validCandidate(candidate) == true);
    votesReceived[candidate] += 1;
  }

  function validCandidate(bytes32 candidate) constant returns (bool) {
    return candidateList[candidate];
  }

}

It's a simple test as follows:

Hope it helps~

Answer 2

Default Value of bool type in solidity is false. A simple smart contract to verify this.Run this in remix and click test.

pragma solidity ^0.4.24;

contract DeafaultValueOfBool{

    bool public test;
}