Mapping in solidity

Hey there, Are you learning solidity and want to know about mapping? Here is an article for you!

Mapping refers to a hash table consisting of key and value type pairs. This can only have a type of storage and is generally used for state variables. It can be marked public. Solidity automatically creates a getter for it.

Below is the syntax:

mapping(_KeyType => _ValueType)

Where:

• **_KeyType **: can be any built-in type plus bytes and string. No reference type or complex objects are allowed.

• ** _ValueType**: can be any type.

Example

pragma solidity ^0.4.18;

contract mappingExample {
    struct student {
        string name;
        string subject;
        uint8 marks;
    }

    // Creating mapping
    mapping (address => student) result;
    address[] student_result;

    // Function adding values to the mapping
    function adding_values() public {
        var student
        = result[0xDEE7796E89C82C36BAdd1375076f39D69FafE252];

        student.name = "John";
        student.subject = "Chemistry";
        student.marks = 88;
        student_result.push(
        0xDEE7796E89C82C36BAdd1375076f39D69FafE252) -1;

    }

    // Function to retrieve
    // values from a mapping
    function get_student_result(
    ) view public returns (address[]) {
        return student_result;
    }
}