Address book Solidity smart contract

Below is a address book Solidity smart contract. It allows one to save a list of Ethereum account address’s to the blockchain with an alias name. As a note never save sensitive or private data to the public blockchain. Data stored on the blockchain is public can be read using various tools (e.g. Web3).

The Address Book contract is advanced as it uses:

  • mappings
  • arrays
  • loop

Experiment with the contract below to learn the basics of mappings, arrays and loops. Try to add or enhance the smart contract code. Deploy it to the test network using Remix. Keep in mind:

  • Saving a state variable to the blockchain uses gas
  • Viewing state variables from the blockchain does not use gas

Try it in Remix

pragma solidity 0.5.10;

contract AddressBook {

    //maps an address to an address array
    //As an example your address to a list of addresses you are interested in.  This supports multiple people having an address book

    mapping(address => address[]) private _addresses;

    //maps an address to another map of address to a string
    //example - your address mapped to a mapping of your address book to its alias

    mapping(address => mapping(address => string)) private _aliases;

    //returns the list of addresses in the _addresses map
    function getAddressArray(address addr) public returns (address[] memory) {
        return _addresses[addr];

    //adds address to your list of addresses in the _addresses map.
    //Uses push since it is an array
    //adds your address, address and alias to the _aliases map
    function addAddress(address addr, string memory alia) public {
        _aliases[msg.sender][addr] = alia;

    function removeAddress(address addr) public {
        // get the length of the addresses in the array from the msg sender
        uint length = _addresses[msg.sender].length;
        for(uint i = 0; i < length; i++) {
            // if the address that you want to remove = one of the addresses you own 
            //and is one of the iterations of the loop
            if (addr == _addresses[msg.sender][i]) {
                //once we find the item in the array we need to delete the item
                //then shift each item down 1.  You can't just delete an item in the middle of an array
                //make sure the length of the address is not < 1 (this is needed because we are going to reorder the array)
                if(1 < _addresses[msg.sender].length && i < length-1) {
                    //shift the last item in the array to the position of the item that we are removing
                    _addresses[msg.sender][i] = _addresses[msg.sender][length-1];

                // delete the item we just swapped from
                delete _addresses[msg.sender][length-1];
                //then decrement the length of the array by 1
                //delete the alias for it
                delete _aliases[msg.sender][addr];

    //Gets the alias for your address
    function getAlias(address addrowner, address addr) public returns (string memory) {
        return _aliases[addrowner][addr];

Try it in Remix

This code is for learning and entertainment purposes only. The address book solidity smart contract code above has not been audited. Use at your own risk. Remember smart contracts are experimental and could contain bugs.

Click here for more information about how to use the Ethereum test network and how to obtain test ETH.

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