Two structs InputReader and OutputWriter for fast and convenient IO in Rust.
The main use of these structs is in competitive programming or Kattis style problems. Reading particularly numbers via io::stdin() is not very convenient. In competitive programming you want to be able to easily get the next number or word in the stream since you know the exact format of the input before hand. The InputReader struct makes that trivial while also being fast.
Regular output in Rust via println!() can also be problematic since it is line buffered. This can make output can be surprisingly slow. The OutputWriter struct buffers all output which results in a much better performance.
To use these in competitive programming simply download input_reader.rs or output_reader.rs. Put them in the same folder as your solution and import it like below.
This was inspired by this amazing Java class but written completely separately.
```Rust // import it mod inputreader; use inputreader::InputReader;
fn main() { // Create a reader from stdin let mut input = InputReader::new();
// ... or from a file let mut input = InputReader::from_file("input.txt");
// ... or from any struct that implements the Read trait. // The reader needs to be wrapped in a Box. // In this example from a tcp stream: let tcpstream = Box::new( TcpStream::connect("127.0.0.1:34254") ); let mut input = InputReader::fromreader(tcp_stream);
// Read numbers and words from the input source simply like this. let x: usize = input.nextusize(); let y: i64 = input.nexti64(); let z: f32 = input.nextf32(); let word: String = input.nextword().tostring(); let line: String = input.nextline().to_string(); } ```
This struct sacrifices some functionality/correctness for performance and convenience:
- Results are unwrapped internally so that the API is much simpler. In competitive programming you will not recover from any IO error anyway.
- UTF8 strings are not supported. The InputReader will treat each byte in the input source as a separate character. This is a significant speed up and in competitive programming only ascii is almost always used anyway.
- It will not do any validation on the size of numbers before trying to fit them in a u8 for example. This is also fine for competitive programming since number bounds are usually given.
- Only parses decimal notation for numbers, not hexadecimal for example.
- It will not parse special float values like NaN or Infinity.
Rust
// Constructs an InputReader which reads from stdin.
InputReader::new() -> Self
Rust
// Constructs an InputReader which reads from the file at the given path.
InputReader::from_file(path: &str) -> Self
Rust
// Constructs an InputReader that reads from the given reader.
InputReader::from_reader(reader: Box<dyn Read>) -> Self
The following methods are pretty self-explanatory. They read the next thing from the input source.
```Rust InputReader::next_usize(&mut self) -> usize
InputReader::nextu8(&mut self) -> u8 InputReader::nextu16(&mut self) -> u16 InputReader::nextu32(&mut self) -> u32 InputReader::nextu64(&mut self) -> u64
InputReader::nexti8(&mut self) -> i8 InputReader::nexti16(&mut self) -> i16 InputReader::nexti32(&mut self) -> i32 InputReader::nexti64(&mut self) -> i64
InputReader::nextf32(&mut self) -> f32 InputReader::nextf64(&mut self) -> f64
// Note that it will not include the newline char InputReader::nextline(&mut self) -> &str InputReader::nextword(&mut self) -> &str ```
The two string methods return a &str instead of a String for optimization reasons. If you need a String that you own you can copy it by doing input.next_word().to_string().
```Rust // Returns true if there is more data to be read, false otherwise. InputReader::has_more(&mut self) -> bool
// Changes the internal buffer size. Default: 2^16 bytes // Will panic if shrinking the buffer would cause data loss. InputReader::setbufsize(&mut self, buf_size: usize) ```
```Rust // import it mod outputwriter; use outputwriter::OutputWriter;
fn main() -> std::io::Result<()> { // Create a writer from stdout let mut output = OutputWriter::new();
// ... or from a file let mut input = OutputWriter::from_file("output.txt");
// ... or from any struct that implements the Write trait. // The writer needs to be wrapped in a Box. // In this example from a tcp stream: let tcpstream = Box::new( TcpStream::connect("127.0.0.1:34254") ); let mut input = OutputWriter::fromwriter(tcp_stream);
// Write to the output source simply like this. output.println("Hello world!"); output.print(&format!("{} is a cool number.\n", 1337));
// It also implements the write trait, so you can do this: write!(output, "{} formatted!\n", "This is")?; writeln!(output, "{} is the answer.", 42)?;
// You can manually flush the writer but this will // be done automatically when the writer is dropped. output.flush()?; Ok() } ```
This class implements the Write trait. This is mostly so we can utilize the write! and writeln! macros but this means several more methods are available on the struct. See documentation here.
Rust
// Constructs an OutputWriter which writes to stdout.
OutputWriter::new() -> Self
Rust
// Constructs an OutputWriter which writes to the file at the given path.
OutputWriter::from_file(path: &str) -> Self
Rust
// Constructs an OutputWriter that writes to the given writer.
OutputWriter::from_writer(reader: Box<dyn Write>) -> Self
```Rust // Writes the string to the output source. OutputWriter::print(&mut self, s: &str)
// Convenience method for writing the given string with a newline appended. OutputWriter::println(&mut self, s: &str) ```