[hcheng] chapter 1.4.12 Default and Value initialization

dev0 · dev0 · commit 9ad248495df7 · 2018-03-27T04:20:49.000-04:00
diff --git a/meta_program/chapter_1_specializtion_and_deduction/default_and_value_initialization.h b/meta_program/chapter_1_specializtion_and_deduction/default_and_value_initialization.h
@@ -0,0 +1,24 @@
+// 1.4.12 Default and Value Initialization
+#include<string>
+class A {
+public:
+	std::string s_;
+	int i_;
+	A(){} // this will default-construct s_ but leave i_ uninitialized
+		  // ch: in c++11, still be this?
+};	
+
+/*Good as following*/
+/*
+ * if T is as class with a default constructor, that will be used
+ * otherwise, the storage for T will be set to 0
+ * if T is an array, each element will be recursively initialized
+ */
+template<typename T>
+struct initialized_value {
+	T result;
+	initialized_value() : result() {
+	}
+};
+
+
diff --git a/meta_program/chapter_1_specializtion_and_deduction/main.cc b/meta_program/chapter_1_specializtion_and_deduction/main.cc
@@ -2,9 +2,22 @@
 //#include "specialization_and_overload.h"
 //#include "specialization_in_class.h"
 #include "tempalte_argument_deduction.h"
+#include "default_and_value_initialization.h"
 using namespace std;
 
 int main(int argc, char** argv) {
+	A a;
+	cout << "a.i_=" << a.i_ << "\n";
+	initialized_value<double> x;
+	cout << "x.result=" << x.result << "\n";
+	initialized_value<double [5]> y;
+	cout << "y.result= ";
+	for (int i = 0;i < 5;++i) {
+		cout << y.result[i] << " ";
+	} 
+	cout << "\n";
+	initialized_value<std::string> z;
+	cout << "z.result = " << z.result << "\n";
 	return 0;
 }
 
