add file io sample

io/io.go

@@ -0,0 +1,44 @@
+package main
+
+import (
+	"bufio"
+	"io"
+	"os"
+)
+
+func main() {
+	fi, err := os.Open("input.txt")
+	if err != nil {
+		panic(err)
+	}
+	defer fi.Close()
+	r := bufio.NewReader(fi)
+
+	fo, err := os.Create("output.txt")
+	if err != nil {
+		panic(err)
+	}
+	defer fo.Close()
+	w := bufio.NewWriter(fo)
+
+	buf := make([]byte, 1024)
+	for {
+		n, err := r.Read(buf)
+		if err != nil && err != io.EOF {
+			panic(err)
+		}
+		if n == 0 {
+			break
+		}
+
+		if n2, err := w.Write(buf[:n]); err != nil {
+			panic(err)
+		} else if n2 != n {
+			panic("error in writing")
+		}
+	}
+
+	if err = w.Flush(); err != nil {
+		panic(err)
+	}
+}