区块链：Solidity值类型(Solidity 字典／映射 Mappings)

语法

mapping(_KeyType => _ValueType)

字典／映射其实就是一个一对一键值存储关系。

{age: 28, height: 172, name: wt}

同一个映射中，可以有多个相同的值，但是键必须具备唯一性。

pragma solidity ^0.4.4;

contract MappingExample {

    mapping(address => uint)  balances;

    function update(address a,uint newBalance) public {
        balances[a] = newBalance;
    }

    function searchBalance(address a) constant public returns (uint) {     
        return balances[a];
    }
}

结构体和字典综合案例

pragma solidity ^0.4.4;

contract CrowdFunding {
    // Defines a new type with two fields.
    struct Funder {
        address addr;
        uint amount;
    }

    struct Campaign {
        address beneficiary;
        uint fundingGoal;
        uint numFunders;
        uint amount;
        mapping (uint => Funder) funders;
    }

    uint numCampaigns;
    mapping (uint => Campaign) campaigns;

    function newCampaign(address beneficiary, uint goal) public returns (uint campaignID) {
        campaignID = numCampaigns++; // campaignID is return variable
        // Creates new struct and saves in storage. We leave out the mapping type.
        campaigns[campaignID] = Campaign(beneficiary, goal, 0, 0);
    }

    function contribute(uint campaignID) public payable {
        Campaign storage c = campaigns[campaignID];
        // Creates a new temporary memory struct, initialised with the given values
        // and copies it over to storage.
        // Note that you can also use Funder(msg.sender, msg.value) to initialise.
        c.funders[c.numFunders++] = Funder({addr: msg.sender, amount: msg.value});
        c.amount += msg.value;
    }

    function checkGoalReached(uint campaignID) public returns (bool reached) {
        Campaign storage c = campaigns[campaignID];
        if (c.amount < c.fundingGoal)
            return false;
        uint amount = c.amount;
        c.amount = 0;
        c.beneficiary.transfer(amount);
        return true;
    }
}