update

basic_content/const/extern_const/file2.cpp

@@ -0,0 +1,11 @@
+#include<iostream>
+/**
+ * by 光城
+ * compile: g++ -o file file2.cpp file1.cpp
+ * execute: ./file
+ */
+extern int ext;
+int main(){
+
+    std::cout<<(ext+10)<<std::endl;
+}