Merge branch 'master' of github.com:pezy/Cpp-Primer

ch02/README.md

@@ -104,7 +104,12 @@ int month = 9, day = 7;
 int month = 09, day = 07;
 ```
 
-The first line's integer is decimal, the second line's integer is octal.
+The first line's integer is decimal.
+
+The second line:
+
+1. `int month = 09` is invalid, cause octal don't have digit `9`.
+2. `day` is octal.
 
 ##Exercise 2.7
 > What values do these literals represent? What type does each
@@ -158,7 +163,7 @@ int input_value = 0;
 std::cin >> input_value;
 ```
 
-(b):---when you compile the code without the argument "-std=c++11", you will get the warning below: 
+(b):---when you compile the code without the argument "-std=c++11", you will get the warning below:
     warning: implicit conversion from 'double' to 'int' changes value from 3.14 to 3.
 ---when you compile the code using "-std=c+11", you will get a error below:
     error: type 'double' cannot be narrowed to 'int' in initializer list
@@ -195,7 +200,7 @@ int main()
 `global_int` is global variable, so the value is zero.
 `local_int` is a local variable which is not uninitialized, so it has a undefined value.
 `local_str` is also a local variable which is not uninitialized, but it has a value that is defined by the class. So it is empty string.
-PS: please read P44 in the English version, P40 in Chinese version to get more. 
+PS: please read P44 in the English version, P40 in Chinese version to get more.
 The note: Uninitialized objects of built-in type defined inside a function body have a undifined value. Objects of class type that we do not explicitly inititalize have a value that is defined by class.
 
 ##Exercise 2.11

ch13/README.md

@@ -266,3 +266,40 @@ for_each(elements, first_free, [this](std::string &rhs){ alloc.destroy(&rhs); })
 The new version is better. Compared to the old one, it doesn't need to worry about the order and decrement.So more straightforward and handy. The only thing to do for using this approach is to add "&" to build the pointers to string pointers.
 
 ## Exercise 13.44 [hpp](ex13_44.h) | [cpp](ex13_44.cpp) | [Test](ex13_44_TEST.cpp)
+
+## Exercise 13.45:
+>Distinguish between an rvalue reference and an lvalue reference.
+
+Definition：
+
+- lvalue reference: reference that can bind to **an lvalue**. (Regular reference)
+- rvalue reference: reference **to an object that is about to be destroyed**.
+
+We can bind an rvalue reference to expression that require conversion, to literals, or to expressions that return an rvalue, but we cannot directly bind an rvalue reference to an lvalue.
+
+```cpp
+int i = 42;
+int &r = i; // lvalue reference
+int &&rr = i; // rvalue reference (Error: i is a lvalue)
+int &r2 = i*42; // lvalue reference (Error: i*42 is a rvalue)
+const int &r3 = i*42; // reference to const (bind to a rvalue)
+int &&rr2 = i*42; // rvalue reference
+```
+
+- lvalue : functions that return lvalue references, assignment, subscript, dereference, and prefix increment/decrement operator.
+- rvalue / const reference : functions that return a nonreferences, arithmetic, relational bitwise, postfix increment/decrement operators.
+
+## Exercise 13.46:
+>Which kind of reference can be bound to the following initializers?
+```cpp
+int f();
+vector<int> vi(100);
+int&& r1 = f();
+int& r2 = vi[0];
+int& r3 = r1;
+int&& r4 = vi[0] * f();
+```
+
+## Exercise 13.47 [hpp](ex13_47.h) | [cpp](ex13_47.cpp)
+
+## [Exercise 13.48](ex13_48.cpp)

ch13/ex13.47.48/string.cpp → ch13/ex13_47.cpp

@@ -5,7 +5,7 @@
  *  @remark
  ***************************************************************************/
 
-#include "string.h"
+#include "ex13_47.h"
 #include <algorithm>
 #include <iostream>
 

ch13/ex13.47.48/main.cpp → ch13/ex13_48.cpp

@@ -17,7 +17,7 @@
 //  std::vector<T> performs reallocation by calling String's copy constructor.
 //  In a word, it depends on the state of std::vector<String>.
 //!
-#include "string.h"
+#include "ex13_47.h"
 #include <vector>
 
 int main()