Hi I have just started to program in Rust. Here is my build.rs use std::fs::{File, self}; use std::io::Write; use std::os::unix::prelude::PermissionsExt; use std::env; use std::path::{Path, PathBuf}; fn main() { let out_dir = env::var_os("CARGO_MANIFEST_DIR").unwrap(); let dest_path: PathBuf = Path::new(&out_dir).join("target/release/Settings.toml"); println!("{:?}", dest_path.as_os_str()); let f = File::create(dest_path); f.as_ref() .unwrap() .write_all("largest_number = 7".as_bytes()) .unwrap(); set_permissions(f); } fn set_permissions(f: Result<File, std::io::Error>)… Read More Unable to set permissions in RUST

what’s different let and const in rust ? for example if use let without mut, is not possible change value fn main(){ let MYINT = 1; MYINT = 2; // error const MYINT_ = 1; MYINT_ = 1; //error } >Solution : const indicates a compile-time constant which means it can only be set to… Read More What is different let ( without mut ) with const

Is there a nice way of creating an array (that already has elements) and copy the elements of another slice into it? I thought of maybe sort-of destructuring it? fn main() { let cmd: u8 = 1; let config: &[u8; 2] = &[2, 3]; let bytes = &[cmd, ..config]; } Playground (does not work –… Read More Copying elements of a slice into a new array

let mut foo: [u8; 6] = &[0, 0, 0, 0, 0, 0] let mut bar: &[u8] = &[1, 2, 3] I want the desired result: &[1, 2, 3, 0, 0, 0] The obvious way: let foo: [u8; 6] = [bar, vec![0; 6 – bar.len()].as_slice()].concat().try_into()… It causes a lot of overhead. It’s not practical Perhaps there… Read More How do I shove a slice into an array?

let mut foo: [u8; 6] = &[0, 0, 0, 0, 0, 0] let mut bar: &[u8] = &[1, 2, 3] I want the desired result: &[1, 2, 3, 0, 0, 0] The obvious way: let foo: [u8; 6] = [bar, vec![0; 6 – bar.len()].as_slice()].concat().try_into()… It causes a lot of overhead. It’s not practical Perhaps there… Read More How do I shove a slice into an array?

I was trying to trace the error in my Rust API code. When I ran it, it showed the following in the terminal: Server running on localhost:3000 auth auth err1 … Notice auth err1 was printed from inside .ok_or() in my code below, but the StatusCode::BAD_REQUEST was not triggered as I got 200 OK back.… Read More Why did error not trigger when println was run?

I would like to get a global variable with BufWriter. This code is executed without errors, but writing to the file is not carried out: lazy_static! { static ref WRITER: Mutex<BufWriter<File>> = { let file = File::create("test.bin").unwrap(); BufWriter::new(file).into() } } WRITER.lock().unwrap().write_all(&vec![1, 2, 3, 4]).unwrap(); >Solution : Two things come into play: A BufWriter absorbes writes… Read More static variable with BufWriter in Rust

I’m new to Rust, so this may be a naive question, but I was looking at the TrustedLen trait and was confused. It describes that a TrustedLen iterator "reports a size hint where it is either exact (lower bound is equal to upper bound), or the upper bound is None." I was curious about the… Read More TrustedLen Iterator from an Iterator that is not implementing TrustedLen

According to my understanding, next needs a &mut Test, but create_test() returns a Test. Why can this be compiled? My guess is that . will implicitly convert Test to &mut Test, I am not sure. Can somebody explain more about this? pub struct Test { t: u64, } fn create_test() -> Test { Test {… Read More Convert T to &mut T with `.`?

Here’s my src/main.rs file: use chrono_tz::Tz; use chrono::FixedOffset; use chrono::{NaiveDateTime, TimeZone, NaiveDate}; fn my_func(from_tz: Tz, ndt: NaiveDateTime){ let res = from_tz.from_local_datetime(&ndt); println!("res: {:?}", res); } fn main() { let area_location: Tz = "UTC".parse().unwrap(); let hour = 3600; let fixed_offset: FixedOffset = FixedOffset::east_opt(5 * hour).unwrap(); let ndt = NaiveDate::from_ymd_opt(2038, 1, 19).unwrap().and_hms_opt(3, 14, 08).unwrap(); my_func(area_location, ndt) }… Read More Write function that accepts two argument types but does the same thing