added stdio example

Author: BartMassey

README.md

@@ -41,3 +41,4 @@ in a controlled repository now.
 * `charcast.rs`: character / number casting examples
 * `lower.rs`: boring character lowercase example
 * `stringchars.rs`: string ←→ chars conversion examples
+* `stdio.rs`: stdio usage example

stdio.rs

@@ -0,0 +1,26 @@
+/// Use `Write` so that `writeln!()` and `write!()` work.
+/// Use `BufRead` so that `stdin.read_line()` works.
+use std::io::{self, Write, BufRead};
+
+fn main() {
+    // Get a handle to stdout. Note that we are not bothering to lock it, because we don't care
+    // about performance and there's no `BufWrite` trait.
+    let mut stdout = io::stdout();
+    // This could just as easily have been `println!()`.
+    writeln!(stdout, "Trying some stuff").unwrap();
+    // Print a prompt and leave the cursor there.
+    write!(stdout, "> ").unwrap();
+    // Without this the prompt won't appear until way late.
+    stdout.flush().unwrap();
+    // Get a handle to stdin. Note that this must be a separate step from locking, because the
+    // locking borrows the handle.
+    let stdin = io::stdin();
+    // Get a locked `StdinLocked` guard. This obeys `BufRead`.
+    let mut stdin = stdin.lock();
+    // Make a placeholder to read a line of text into.
+    let mut msg = String::new();
+    // Read a line of text as a side effect in `msg`.
+    let _ = stdin.read_line(&mut msg).unwrap();
+    // Show the line, trimming off the line ending (and any whitespace).
+    eprintln!("Got {}", msg.trim_end());
+}