Let's imagine I have this account and I want to filter all the Program Accounts by the author:

pub struct EntryBook {
    title: String,
    author: String

How would be the offset to target the author property?

const filteringBooks = await program.account.entryBook.all([
          memcmp: {
              offset: 8 +    // Discriminator.
                      4 +    // Title string prefix.
                      ?????  // Title String 
                      4,     // Author string prefix.
              bytes: bs58.encode(Buffer.from('<author name>')),

2 Answers 2


You need to pack them into fixed lengths byte arrays. This is the downside of memcmp: you can't have variable length fields. The following is an easy way to do so:

pub fn pack_string_in_32_bytes(string: String) -> Result<[u8; 32]> {
    let string_in_bytes = string.as_bytes();

    if string_in_bytes.len() > 32 {
        return Err(error!(CustomProgramError::StringTooLong));

    let mut bytes: [u8; 32] = [0; 32];


You would have to make title a fixed length in order for the offset to work in this way. e.g. title: [u8; 10] Then just pad the end of the title string with empty space if it doesn't fill up the full fixed length.


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