From dd7b707acf711fa453838538e77ee75e0fbb8a2d Mon Sep 17 00:00:00 2001
From: gliangbupt <gliangjlu@163.com>
Date: Sun, 17 Jul 2022 18:42:17 +0800
Subject: [PATCH] book: add missing header file (#233)

---
 book/en-us/02-usability.md | 2 ++
 book/zh-cn/02-usability.md | 2 ++
 2 files changed, 4 insertions(+)

diff --git a/book/en-us/02-usability.md b/book/en-us/02-usability.md
index ee90837..79a754f 100644
--- a/book/en-us/02-usability.md
+++ b/book/en-us/02-usability.md
@@ -285,6 +285,8 @@ such as:
 ```cpp
 #include <initializer_list>
 #include <vector>
+#include <iostream>
+
 class MagicFoo {
 public:
     std::vector<int> vec;
diff --git a/book/zh-cn/02-usability.md b/book/zh-cn/02-usability.md
index a12bacb..8b1731c 100644
--- a/book/zh-cn/02-usability.md
+++ b/book/zh-cn/02-usability.md
@@ -233,6 +233,8 @@ int main() {
 ```cpp
 #include <initializer_list>
 #include <vector>
+#include <iostream>
+
 class MagicFoo {
 public:
     std::vector<int> vec;