solidity智能合约[26]-mapping

mapping

mapping是一张表，存储key-value对。更准确的说，mapping是一张hash映射表，内部并没有存储真实的key值。

Mappings can be seen as hashtables which are virtually initialized such that every possible key exists and is mapped to a value whose byte-representation is all zeros: a type’s default value. The similarity ends here, though: The key data is not actually stored in a mapping, only its keccak256 hash used to look up the value.

Because of this, mappings do not have a length or a concept of a key or value being “set”.

mapping用例

下面的案例模拟了一个登陆网站，将地址与id绑定在一起。id又与姓名绑定在一起。

pragma solidity ^0.4.23;
contract mappingTest{

    uint id = 0;

   mapping(address =>uint) idmap;//将地址与id绑定在一起
   mapping(uint =>string) namemap;//id又与姓名绑定在一起。

   //注册
   function regist(string name) public{
       address acount = msg.sender;
       id++;
       idmap[acount] =  id;
       namemap[id] =  name;
   }
   //根据地址获取id
   function getIdByAddress(address _address) public view returns(uint){
       return  idmap[_address];
   }
      //根据id获取名字
      function getNameByID(uint _id)  public view returns(string){
       return  namemap[_id];
   }
}