My thoughts on new things in C++11

1. New in C++11
Trần Duy Quang – May 2014

2. Agenda
1. Automatic variables
2. Decltype
3. Rvalue reference
4. Lambda function
5. Variadic template
6. Concurrency library
2

3. Compiler support
3
VS 2010
Automatic
variables
Decltype
Rvalue
reference
Lambda
function
VS 2012
Concurrency
library
Memory
model
VS 2013
Variadic
template
Custom
literal
Delegating
constructor
VS 13: Some C++14 features!

4. auto Variables
 Implicit variable declaration
 Keyword: auto
Note: cbegin to iterate constant, no change in content 4

5. Careful: auto default
 By-value for references
 Use auto& or decltype for desired result!
5
int f, not int& f!

6. More mindblow
 int&: auto is int (only, no &)
 But int*: auto is int* !
6

7. std::bind
 Placeholder objects _1, _2, .., _N
 C# alike
7
1. May cause runtime error, but when?
2. What about _10 rather than _2?

8. Range-based for loop
8
Better? auto&!

9. decltype
 Query the type of an expression
 Primary use in generic programming1
Why do we have to use auto & decltype here?
1Algorithms are written in terms of to-be-specified-later types that are then instantiated when needed for specific types provided as parameters 9

10. auto without decltype
 Compile error
10

11. Why auto & decltype?
11

12. Parenthesized variable
 Always a reference!
12

13. decltype vs auto
 decltype of a variable
 returns the type of that variable, including top-level
const and references
 decltype depends on its form of variable
 Parenthesis always yield a reference
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C++ Primer 2014:

14. What do we have?
14
Type of x
Type of y
Why?
decltype(x) y auto y = x
const int const int int Strips top-level cv-qualifiers
int[100] int[100] int* Performs array to pointer conversion
int f (int) int f (int) int (*) (int) Performs function to function pointer
conversion
int& int& int Auto remove references
int&& int&& int
Don’t forget the reference with parenthesis from decltype! decltype( (x) )

15. auto vs decltype conclustion
 auto
 Everyday use
 Assign the value of some expression to a new variable
 decltype
 Template & generic programming (library code)
 a new variable with precisely the same type
15

16. More mindblow (again)
 decltype(auto) f = expression; // C++14
 C++17 will go further? No ideas!
16

17. Lambda function
17

18. Lambda function
 []: capture list
 [] () -> return type
18

19. Lambda capture
 Capture by value
 42
 Capture by reference
 43
 43
 (Can be modify
inside, but not affect
outside)
19

20. Types of capture
 [=]: automatic capture all by value
 [&]: automatic capture all by reference
 [this]: capture this pointer by value
 [a, &b]: capture a by value and b by reference
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21. Recursive lambda
21

22. Stateless lambda
 Convertible to function pointer!
 Used with C-style API (e.g. Win32)
22

23. High-order function
 Takes one or more functions as an input
 Outputs a function
23
Sắp xếp tăng dần

24. Generic lambda
 Take a deep breath! (C++14 only)
 We can write
 auto auto (auto auto) { auto; };
 Compiler infers the rest from the context
 Actually, this is NOT a type deduction
 This is a template!
24

25. Let’s see one generic lambda
25 Did I tell you about functor?

26. Lambda physiology
 For each lambda compiler generate a class
 Specifying lambda instantiate an object
 Invoking lambda call the object’s operator()
26

27. Rvalue reference
27

28. Rvalue definition
 lvalue: can appear on the left and right
 rvalue: can only appear on the right
28

29. Move semantics
 What do we need from the last line?
 Destruct the resource held by hello first
 Clone resource from temp returned
 Destruct temp & release its resources
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 More efficient?
 Swap resources pointers
 Let temp destructor destruct hello’s original resources

30. Obvious solution
 Overload operator= ! (Copy assignment)
 Right hand side should be passed by reference
 rvalue references!
 MyString&&: rvalue reference to MyString&
30

31. Function overload resolution
 “Am I being called on an lvalue or rvalue?”
31

32. Achieving move semantics
 Should occur only for copy constructor and
assignment operator!
32

33. Forcing move semantics
 std::move help
 Type with no move semantics implementation?
 Swap like old times!
33

34. Funny jokes
34

35. Smart pointers
35

36. Three types of smart pointer
 unique_ptr<T> - Single ownership
 Deleted when pointer dies
 shared_ptr<T> - Shared ownership
 Reference pointer counting
 weak_ptr<T> - Cycle breaking
 auto_ptr deprecated!
36

37. Before we go on
 Resource Acquisition Is Initialization (RAII)
37

38.  RAII in C++ has been around for over a decade
 C++11 encourages its use as default
 Smart pointers help building RAII around legacy
interfaces
 Move semantics makes passing resources around
cheap
38

39. unique_ptr
39

40. shared_ptr
 Last pointer dies, object is deleted
40

41. weak_ptr
 Does not affect reference count
 Break cycles between shared_ptrs
41

42. Some other things
42

43. Threads & Async
43

44. Variadic template
44

45. Rules of expansion
45

46. Initializer list
46

47. using
47

48. Raw string literals
48

49. Other examples of raw string literals
49

50. Tuple
50

51. Default & delete
51

52. The last coffee drop
52

53. C++ Accelerated Massive
Parallelism
53

54. Simple example
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Normal version AMP version

55. Basic elements of AMP
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Code run on
each thread
Thread id
running the
lambda
Check if code can run
with AMP / Direct3D

56. Reference 1
 Slide C++11
 Slide What’s new in C++11
 Slide The future of C++
 Slide The style of C++11
 Slide C++11
 Slide C++11 idioms
 Slide What’s new in Visual C++11
 Slide C++11 – Feel the new language
 Slide C++11 Talk
56

57. Reference 2
 Slide C++11 – A change in style
 Slide New C++ Standard – C++11
 Slide Advanced C++ runtime improvement
techniques
 Slide Hot C+11 Rvalue references and Move
semantics
 Slide C++ usage experience
57

58. Reference 3
 Ebook C++11 for programmers 2014
 Ebook C++ Primer 5th Edition 2013
 Ebook C Primer Plus 2014
 Ebook Effective C++ 3rd Ed 55 Specific Ways to
Improve Your Programs and Designs 2005
 Ebook Effective C++ & More effective C++
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