# How to save strings in the storage of dapp?

**URL:** <https://forum.fuel.network/t/how-to-save-strings-in-the-storage-of-dapp/735>\
**Category:** Sway\
**Created:** [December 15, 2022, 1:25am UTC](https://forum.fuel.network/t/how-to-save-strings-in-the-storage-of-dapp/735 "2022-12-15T01:25:19Z")\
**Posts on this page:** 4\
**Page:** 1

<div class="post-metadata">

**Author:** ![fuel](https://sea2.discourse-cdn.com/flex022/user_avatar/forum.fuel.network/fuel/32/1677_2.png) [@fuel](https://forum.fuel.network/u/fuel)\
**Post date:** [December 15, 2022, 1:25am UTC](https://forum.fuel.network/t/how-to-save-strings-in-the-storage-of-dapp/735/1 "2022-12-15T01:25:19Z")

</div>

Hello everyone!  
In an attempt to implement a token contract on fuel I forked swayswap’s token contract and noticed that swayswap’s token doesn’t support the same fields like `name`, `symbol`, and `decimals`.

Then in [one of my previous topics](https://forum.fuel.network/t/which-token-contract-i-should-to-use/373) @david sent me a topic with [src-20 fungible token standard](https://forum.fuel.network/t/src-20-fungible-token-standard/186), but there is no `name`, `symbol` implementation too…  
And today I decided to figure out how I can store strings in the storage.

In the progress of my research I found some solutions, let’s take a closer look at them:

1. First of all I decided to use `str[n]` like a string. But there is one big minus: we definitely need to know the length of the line.  
In that case, we can hardcode some strings before deploying the dApp, but it’s impossible to change the strings.

```auto
contract;

abi MyContract {
     #[storage(read)]
    fn name() -> str[9];
}

storage {
    name: str[9] = "sway gang",
}

impl MyContract for Contract {
     #[storage(read)]
    fn name() -> str[9] {
        storage.name
    }
}

```

1. The next thing that came to my mind is store strings like `str[32]`. Here we can store and change strings less than 32 symbols like `sway gang _______________________ ` and each time you write/read remove/add to the end of the line symbols `_` in quantity `32 - string_length`. But it looks ugly and not convenient.

```auto
contract;

abi MyContract {
     #[storage(read)]
    fn name() -> str[32];
     #[storage(write)]
    fn set_name(name: str[32]);
}

storage {
    name: str[32] = "sway gang _______________________",
}

impl MyContract for Contract {
    #[storage(read)]
    fn name() -> str[32] {
        storage.name
    }

    #[storage(write)]
    fn set_name(name: str[32]){
        storage.name = name;
    }
}

```

1. After that I discovered there is awesome package [sway\_libs::string::String](https://github.com/FuelLabs/sway-libs/tree/master/sway_libs/src/string). And we can use it very well but… Yup the strings library is excellent for dynamically-sized strings. That type does not work in a storage block though because it’s a heap type.  
Btw I will show what the code can look like. Anyway you can copy the code and use Strings without storage

**Forc.toml**

```auto
[project]
authors = ["SWAY GANG"]
entry = "main.sw"
license = "Apache-2.0"
name = "name_contract"

[dependencies]
sway_libs = { git = "https://github.com/FuelLabs/sway-libs", tag = "v0.4.1" }

```

**main.sw**

```auto
contract;
use sway_libs::string::String;

abi MyContract {
     #[storage(read)]
    fn name() -> String;
     #[storage(write)]
    fn set_name(name: String);
}

storage {
    name: String = String::new(), // here code is wrong
}

impl MyContract for Contract {
    #[storage(read)]
    fn name() -> String {
        storage.name
    }

    #[storage(write)]
    fn set_name(name: String){
        storage.name = name;
    }
}

```

1. So, as under the hood package [sway\_libs::string::String](https://github.com/FuelLabs/sway-libs/tree/master/sway_libs/src/string) use `Vec<u8>` my final try was with using `StorageVec<u8>`. The contract will look like that

```auto
contract;
use std::{storage::StorageVec};
abi MyContract {
    #[storage(read)]
    fn name() -> StorageVec<u8>;
    // todo
    // #[storage(write)]
    // fn set_name(name: StorageVec<u8>);
}

storage {
    name: StorageVec<u64> = StorageVec {}, 
}

impl MyContract for Contract {
    #[storage(read)]
    fn name() -> StorageVec<u8> {
        storage.name
    }

    // todo
    // #[storage(write)]
    // fn set_name(name: StorageVec<u8>){
    // storage.name = name;
    // }
}

```

and the test will look like tahat:

```auto
use fuels::{prelude::*, tx::ContractId};

abigen!(MyContract, "out/debug/name_contract-abi.json");

async fn get_contract_instance() -> (MyContract, ContractId) {
    let mut wallets = launch_custom_provider_and_get_wallets(
        WalletsConfig::new(
            Some(1),           
            Some(1),             
            Some(1_000_000_000), 
        ),
        None,
        None,
    )
    .await;
    let wallet = wallets.pop().unwrap();

    let id = Contract::deploy(
        "./out/debug/name_contract.bin",
        &wallet,
        TxParameters::default(),
        StorageConfiguration::with_storage_path(Some(
            "./out/debug/name_contract-storage_slots.json".to_string(),
        )),
    )
    .await
    .unwrap();

    let instance = MyContract::new(id.clone(), wallet);

    (instance, id.into())
}

#[tokio::test]
async fn can_get_contract_id() {
    let (_instance, _id) = get_contract_instance().await;
    // todo
    // _instance.methods().set_name("SWAY GANG".as_bytes()).call().await.unwrap()
}

```

But after  
`forc build` and `cargo test` it It’s falling with this error

```auto
error[E0392]: parameter `V` is never used
 --> tests/harness.rs:3:1
  |
3 | abigen!(MyContract, "out/debug/name_contract-abi.json");
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unused parameter
  |
  = help: consider removing `V`, referring to it in a field, or using a marker such as `PhantomData`
  = note: this error originates in the macro `abigen` (in Nightly builds, run with -Z macro-backtrace for more info)

For more information about this error, try `rustc --explain E0392`.
error: could not compile `name-contract` due to previous error

```

**So, can someone explain to me what I’m doing wrong and how I store and update the name in the dApp store?**

---

<div class="post-metadata">

**Author:** ![mohammadfawaz](https://avatars.discourse-cdn.com/v4/letter/m/e56c9b/32.png) [@mohammadfawaz](https://forum.fuel.network/u/mohammadfawaz)\
**Post date:** [December 21, 2022, 2:20pm UTC](https://forum.fuel.network/t/how-to-save-strings-in-the-storage-of-dapp/735/2 "2022-12-21T14:20:36Z")

</div>

Yeah unfortunately, `str[n]` is your only reasonable option at this point. This may change in the future as we make strings a bit more ergonomic.

Dynamic strings (i.e. `String) and `StorageVec` have various limitations that you ran into already.

---

<div class="post-metadata">

**Author:** ![fuel](https://sea2.discourse-cdn.com/flex022/user_avatar/forum.fuel.network/fuel/32/1677_2.png) [@fuel](https://forum.fuel.network/u/fuel)\
**Post date:** [December 21, 2022, 2:51pm UTC](https://forum.fuel.network/t/how-to-save-strings-in-the-storage-of-dapp/735/3 "2022-12-21T14:51:58Z")

</div>

I resolved this like that

```auto
...

pub struct Config {
    name: str[32],
    symbol: str[8],
    decimals: u8,
}

storage {
    config: Config = Config {
        name: " ",
        symbol: " ",
        decimals: 1u8,
    },
    owner: Address = Address {
        value: ZERO_B256,
    },
    mint_amount: u64 = 0,
    mint_list: StorageMap<Address, bool> = StorageMap {},
}

...

#[storage(read)]
    fn config() -> Config {
        storage.config
    }

...

```

---

<div class="post-metadata">

**Author:** ![system](https://us1.discourse-cdn.com/flex022/uploads/fuel/original/2X/5/57d5a345cc15a64b636e0d56e042857f8a0e80b1.png) [@system](https://forum.fuel.network/u/system)\
**Post date:** [January 30, 2023, 12:15pm UTC](https://forum.fuel.network/t/how-to-save-strings-in-the-storage-of-dapp/735/4 "2023-01-30T12:15:39Z")

</div>

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