fmt: add example for Fscanln

Updates golang/go#27376.

Change-Id: I9f33233f1aafa10941a63fcb4e49d351ea7ee246
Reviewed-on: https://go-review.googlesource.com/132675
Reviewed-by: Kevin Burke <kev@inburke.com>
Run-TryBot: Kevin Burke <kev@inburke.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/fmt/example_test.go

@@ -6,6 +6,7 @@ package fmt_test
 
 import (
 	"fmt"
+	"io"
 	"os"
 	"strings"
 )
@@ -77,3 +78,25 @@ func ExampleFprintln() {
 	// there are 99 gophers
 	// 21
 }
+
+func ExampleFscanln() {
+	s := `dmr 1771 1.61803398875
+	ken 271828 3.14159`
+	r := strings.NewReader(s)
+	var a string
+	var b int
+	var c float64
+	for {
+		n, err := fmt.Fscanln(r, &a, &b, &c)
+		if err == io.EOF {
+			break
+		}
+		if err != nil {
+			panic(err)
+		}
+		fmt.Printf("%d: %s, %d, %f\n", n, a, b, c)
+	}
+	// Output:
+	// 3: dmr, 1771, 1.618034
+	// 3: ken, 271828, 3.141590
+}