Fixed-size byte arrays - Solidity Part 3.1.10

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In Solidity, fixed-sized byte arrays are essential for managing and storing binary data efficiently. They are a powerful feature of the language, offering specific operators and a length member that facilitate their manipulation. This post will dive into the intricacies of fixed-sized byte arrays, including their operators and the length member.

Source Code: https://github.com/scaihai/enkwadore-blog-blockchain-demos/tree/main/solidity/contracts/3.1.10

What Are Fixed-Sized Byte Arrays?

Fixed-sized byte arrays in Solidity are used to store sequences of bytes with a predefined length. They are declared using the bytesN type, where N specifies the number of bytes in the array. For instance, bytes32 denotes a byte array of 32 bytes.

Here’s a quick example of declaring and initializing a fixed-sized byte array:

bytes32 myBytes = "Hello, Solidity!";

In this example, myBytes is a bytes32 array initialized with the string “Hello, Solidity!”. Note that if the string exceeds the length of bytes32, it will be truncated.

Operators for Fixed-Sized Byte Arrays

Fixed-sized byte arrays support various operators that facilitate their manipulation:

  1. Assignment Operator (=): Allows you to assign one fixed-sized byte array to another of the same size.
    bytes32 a = "Solidity";
    bytes32 b = a; // b now holds the value of a
  2. Equality Operator (==): Checks if two fixed-sized byte arrays of the same size are equal.
    bytes32 a = "Solidity";
    bytes32 b = "Solidity";
    bool isEqual = (a == b); // isEqual is true
  3. Inequality Operator (!=): Checks if two fixed-sized byte arrays of the same size are not equal.
    bytes32 a = "Solidity";
    bytes32 b = "Solidity!";
    bool isNotEqual = (a != b); // isNotEqual is true
  4. Indexing Operator ([]): Accesses individual bytes in the array. Indexing starts from 0.
    bytes32 a = "Solidity";
    bytes1 firstByte = a[0]; // 'S'

Members of Fixed-Sized Byte Arrays

Fixed-sized byte arrays come with a length member which returns the length of the byte array. For fixed-sized byte arrays, this length is constant and determined at compile-time.
bytes32 a = "Solidity";
uint length = a.length; // length is 32

Practical Use Cases

Fixed-sized byte arrays are particularly useful in scenarios where:

  • Storage Efficiency: The exact size of the data is known beforehand, which helps in efficient storage and retrieval.
  • Binary Data Handling: When dealing with fixed-size binary data, such as hashes or fixed-length encoded data.

Example Code

Here’s an example of using fixed-sized byte arrays to store and compare hashes:

ByteArrayExample.sol

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

contract ByteArrayExample {
    bytes32 public hash1;
    bytes32 public hash2;
    bytes32 fixedArray = "Solidity"; 

    function setHashes(bytes32 _hash1, bytes32 _hash2) public {
        hash1 = _hash1;
        hash2 = _hash2;
    }

    function areHashesEqual() public view returns (bool) {
        return hash1 == hash2;
    }
}

In this contract, two fixed-sized byte arrays (hash1 and hash2) are used to store hashes. The areHashesEqual function compares them to determine if they are identical.

Conclusion

Fixed-sized byte arrays are a fundamental aspect of Solidity, providing efficient and structured ways to handle binary data. By understanding their operators and members, you can leverage their full potential in your smart contracts. Whether you’re working with hashes or fixed-length data, these arrays are a powerful tool in your Solidity toolkit.

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