Writing Files

Writing files is a fundamental operation in Rust programming. The standard library provides several ways to write data to files, each suited for different use cases - from simple one-shot writes to buffered streaming writes for optimal performance.

Creating and Writing Files

The simplest way to write a file is using std::fs::write:

use std::fs;
 
fs::write("output.txt", "Hello, World!")?;

For more control, use File::create with Write trait methods:

use std::fs::File;
use std::io::Write;
 
let mut file = File::create("output.txt")?;
file.write_all(b"Hello, World!")?;

Buffered Writing with BufWriter

For many small writes, BufWriter provides efficient buffering:

use std::fs::File;
use std::io::{BufWriter, Write};
 
let file = File::create("output.txt")?;
let mut writer = BufWriter::new(file);
 
for i in 1..=1000 {
    writeln!(writer, "Line {}", i)?;
}
// Buffer is automatically flushed when writer is dropped

The BufWriter collects writes in memory and flushes them to disk in larger chunks, which is significantly more efficient for many small writes.

Appending to Files

To add content to an existing file without overwriting:

use std::fs::OpenOptions;
use std::io::Write;
 
let mut file = OpenOptions::new()
    .append(true)
    .create(true)
    .open("log.txt")?;
 
writeln!(file, "New log entry")?;

Your Task

Implement the following functions for writing file contents:

  1. write_string(path: &str, content: &str) -> Result<(), io::Error> - Write a string to a file, creating or overwriting it
  2. write_bytes(path: &str, data: &[u8]) -> Result<(), io::Error> - Write raw bytes to a file
  3. append_string(path: &str, content: &str) -> Result<(), io::Error> - Append a string to a file (create if it doesn't exist)
  4. write_lines(path: &str, lines: &[&str]) -> Result<(), io::Error> - Write multiple lines to a file (each followed by a newline)
  5. write_with_buffer(path: &str, chunks: &[&str]) -> Result<(), io::Error> - Write multiple chunks using buffered writing for efficiency

Examples

 
// Write a simple string
write_string("hello.txt", "Hello, World!")?;
// File now contains: Hello, World!
 
// Write raw bytes
write_bytes(
    "binary.dat",
    &[0x48, 0x65, 0x6c, 0x6c, 0x6f]
)?;
// File now contains: Hello (as bytes)
 
// Append to a file
write_string("log.txt", "First entry\n")?;
append_string("log.txt", "Second entry\n")?;
// File now contains:
// First entry
// Second entry
 
// Write multiple lines
write_lines(
    "list.txt",
    &["Apple", "Banana", "Cherry"]
)?;
// File now contains:
// Apple
// Banana
// Cherry
 
// Efficient buffered writing
write_with_buffer(
    "output.txt",
    &["Hello, ", "World", "!"]
)?;
// File now contains: Hello, World!

Hints
Click here for hints
  • Use std::fs::write for the simplest way to write a string or bytes to a file
  • Use OpenOptions::new().append(true).create(true) .open(path) to open a file for appending
  • Use BufWriter::new(File::create(path)?) to create a buffered writer
  • The writeln! macro writes a line followed by a newline character
  • Use write! or write_all for writing without a trailing newline
  • Remember to handle the Result type returned by all I/O operations
  • BufWriter automatically flushes when dropped, but you can call .flush() explicitly if needed