Ethereum Cookbook

Mapping

Follow these steps to create mappings in solidity:

1. Mappings are created with key-value pairs. A mapping can be compared with a hash table or dictionary. The following example creates a mapping of an address and a user-defined type, and another mapping with an address and an unsigned integer. These are used for storing employee data:

contract test {    struct Person {        uint id;        string name;    }        mapping(address => Person) employees;        mapping(address => uint) balances;        function insert(address _employee, uint _id,         string _name, uint _balance) public {        employees[_employee] = Person({            id: _id,            name: _name        });        balances[_employee] = _balance;    }}

2. Mappings can be nested to create a more complex data structure:

contract test {     mapping(address ...