ch7: add ch7-write123 example

ch7/ch7-write123/Cargo.toml

@@ -0,0 +1,8 @@
+[package]
+name = "write123"
+version = "0.1.0"
+authors = ["Tim McNamara <author@rustinaction.com>"]
+edition = "2018"
+
+[dependencies]
+byteorder = "1.2"

ch7/ch7-write123/src/main.rs

@@ -0,0 +1,36 @@
+use std::io::Cursor;
+use byteorder::{LittleEndian};
+use byteorder::{ReadBytesExt, WriteBytesExt};
+
+fn write_numbers_to_file() -> (u32, i8, f64) {
+    let mut w = vec![]; // slices implement Read and Write, and can thus act as mock files
+
+    let one: u32   = 1;
+    let two: i8    = 2;
+    let three: f64 = 3.0;
+
+    w.write_u32::<LittleEndian>(one).unwrap();
+    println!("{:?}", &w);
+
+    w.write_i8(two).unwrap(); // single byte methods don't take an endianness parameter
+    println!("{:?}", &w);
+
+    w.write_f64::<LittleEndian>(three).unwrap();
+    println!("{:?}", &w);
+
+    (one, two, three)
+}
+
+fn read_numbers_from_file() -> (u32, i8, f64) {
+    let mut r = Cursor::new(vec![1, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 8, 64]);
+    let one_ = r.read_u32::<LittleEndian>().unwrap();
+    let two_ = r.read_i8().unwrap();
+    let three_ = r.read_f64::<LittleEndian>().unwrap();
+
+    (one_, two_, three_)
+}
+
+fn main() {
+    write_numbers_to_file();
+    read_numbers_from_file();
+}