Defining program state

Program state refers to data that is associated with and can be manipulated by your program; it is essentially your program’s database.

You need to define program state when writing Solana programs because Solana programs are stateless by default — they don't store data between transactions. If your program needs to remember anything (e.g. user balances, votes, ownership, or config settings), you must explicitly define and manage that data.

Program state is defined using Rust structs. The struct exists only at the code level, helping you understand and manipulate the data while writing the program, but it’s just a logical representation. Solana itself doesn’t know what a "struct" is.

On-chain, Solana accounts don’t store data as structs, they store raw bytes. To save or load your struct from an account, you must serialize it into bytes (when storing) and deserialize it from bytes (when reading). That’s where serialization libraries like Borsh come in.

Creating your counter program’s state

Start by creating state.rs file in your src folder for modularity. In your file, create a CounterAccount struct with a u64 count property.

Like so:

pub struct CounterAccount {
   pub count: u64,
}

The count property will keep track of your counter account’s current value.

Next, import Borsh’s BorshDeserialize and BorshSerialize traits and implement them for your struct. Like so:

use borsh::{BorshDeserialize, BorshSerialize};

#[derive(BorshSerialize, BorshDeserialize, Debug)]
pub struct CounterAccount {
    pub count: u64,
}

This allows your CounterAccount struct to be converted to and from raw bytes.

Now that you have defined your program’s state, next you need to define the instructions your program can perform.