added 7.43~7.46

ch07/README.md

@@ -261,3 +261,19 @@ private:
   std::string pubdate_;
 };
 ```
+
+## [Exercise 7.43](ex7_43.cpp)
+## Exercise 7.44
+
+illegal, cause there are ten elements, each would be default initialized. But no default initializer for the temporary object.
+
+## Exercise 7.45
+
+No problem. cause `C` have the default constructor.
+
+## Exercise 7.46
+
+- a) A class must provide at least one constructor. (**unture**, "The compiler-generated constructor is known as the synthesized default constructor.")
+- b) A default constructor is a constructor with an empty parameter list. (**unture**,  A default constructor is a constructor that is used if no initializer is supplied)
+- c) If there are no meaningful default values for a class, the class should not provide a default constructor. (**unture**, the class should provide.)
+- d) If a class does not define a default constructor, the compiler generates one that initializes each data member to the default value of its associated type. (**unture**, only if our class does not explicitly define any constructors, the compiler will implicitly define the default constructor for us.)

ch07/ex7_43.cpp

@@ -0,0 +1,29 @@
+//
+//  ex7_43.cpp
+//  Exercise 7.43
+//
+//  Created by pezy on 11/20/14.
+//  Copyright (c) 2014 pezy. All rights reserved.
+//
+
+#include <vector> 
+
+class NoDefault {
+public:
+    NoDefault(int i) { }
+};
+
+class C {
+public:
+    C() : def(0) { } // define the constructor of C.
+private:
+    NoDefault def;
+};
+
+int main()
+{
+    C c;
+
+    std::vector<C> vec(10); 
+    return 0;
+}