Applied C Fri

Transcription

1 Applied C Fri

2 Outline Introduction Auto-Type Inference Lambda Functions Threading Compiling

3 C++11 C++11 (formerly known as C++0x) is the most recent version of the standard of the C++ Approved by ISO(International Organization for Standardization) on 12 August 2011 Includes several additions to the core language and extends the C++ standard library

4 Core language usability enhancements: Primary purpose is to make the language easier to use Improve type safety Minimize code repetition Make erroneous code less likely

5 Auto Type Inference The compiler can infer the type of a variable at the point of declaration: i n t x = 5 ; auto x = 4 ; Very helpful when working with templates and iterators: v e c t o r <i n t > vec ; auto i t r = vec. i t e r a t o r ( ) ; // i n s t e a d o f v e c t o r <i n t > : : i t e r a t o r i t r

6 Study Case t e m p l a t e <typename BuiltType, typename B u i l d e r > void makeandprocessobject ( const B u i l d e r& b u i l d e r ) { B u i l t T y p e v a l = b u i l d e r. makeobject ( ) ; // do s t u f f w i t h v a l two necessary template parameters type of the builder object type of the object being built MyObjBuilder b u i l d e r ; makeandprocessobject<myobj>( b u i l d e r ) ;

7 Study Case (cont.) By using `auto' no longer need to write the specic type of the built object t e m p l a t e <typename B u i l d e r > void makeandprocessobject ( const B u i l d e r& b u i l d e r ) { auto v a l = b u i l d e r. makeobject ( ) ; // do s t u f f w i t h v a l MyObjBuilder b u i l d e r ; makeandprocessobject ( b u i l d e r ) ;

8 Lambda Functions Lambda Function: is a function dened, and possibly called, without being bound to an identier you can write inline in your source code convenient to pass as an argument to a higher-order function allow to create entirely new ways of writing programs

9 Basic Lambda Syntax #i n c l u d e <i o s t r e a m > u s i n g namespace s t d ; i n t main ( ) { [ ] ( ) { cout << " H e l l o, World! " ; ( ) ; []: capture specier, species for the compiler creation of a lambda function (): argument list What about return values?

10 More on the Lambda Syntax If there is no return statement, uses void as default If you have a simple return expression, the compiler will deduce the type of the return value // c o m p i l e r knows t h i s r e t u r n s an i n t e g e r [ ] ( ) { r e t u r n 1 ; specify the return value explicitly // now we ' r e t e l l i n g t h e c o m p i l e r what we want [ ] ( ) > i n t { r e t u r n 1 ;

11 Example: Sorting a list We create a list of cities. // D e f i n e a c l a s s f o r a c i t y c l a s s C i t y { p u b l i c : i n t p o p u l a t i o n ; i n t f o u n d a t i o n _ y e a r ; i n t s u r f a c e _ a r e a ; ; i n t main ( ) { s t d : : l i s t <C i t y > c i t i e s ; // F i l l t h e l i s t w i t h d a t a To sort a set of objects, we have to dene a comparison function.

12 Example: Sorting a list (cont.) In the STL, comparison functions have two arguments, and return true if the rst argument goes before the second. To sort by population, we can dene a compare function: b o o l compare ( C i t y a, C i t y b ) { r e t u r n a. p o p u l a t i o n < b. p o p u l a t i o n ;... c i t i e s. s o r t ( compare ) ; Alternatively, we can use a lambda function: c i t i e s. s o r t ( [ ] ( C i t y a, C i t y b) >b o o l { r e t u r n a. p u p u l a t i o n < b. p o p u l a t i o n ; ) ;

13 Multithreading C++11 threads are more convenient than directly using Posix threads. #i n c l u d e <t h r e a d > i n t main ( ) {... // D e c l a r i n g t h r e a d s s t d : : t h r e a d t ; // A s s i g n a f u n c t i o n t = s t d : : t h r e a d ( f u n c t i o n, a r g u m e n t s ) ;... // F i n a l i z i n g t. j o i n ( ) ; Compile with the ag -pthread

14 Multithreading example: Dot product // D e f i n i t i o n o f a c l a s s t o s t o r e t h e v a l u e s c l a s s P a r t i a l D P { p u b l i c : double d o t p r o d u c t ; double * x ; double * y ; i n t f i r s t ; // F i r s t i n d e x o f a r r a y i n t l e n g t h ; // Count o f e l e m e n t s P a r t i a l D P ( ) : d o t p r o d u c t ( 0 ) { s e t ( double * x i n, double * y i n, i n t f, i n t l ) { x = x i n ; y = y i n ; f i r s t = f ; l e n g t h = l ; ; o p e r a t o r ( ) ( ) { f o r ( i n t i = f i r s t ; i < f i r s t + l e n g t h ; i ++) { d o t p r o d u c t += x [ i ] + y [ i ] ;

15 Multithreading example (cont.) #i n c l u d e <t h r e a d > const i n t s i z e = , n t h r e a d s = 4 ; i n t main ( ) { s t d : : t h r e a d t [ n t h r e a d s ] ; double x [ s i z e ], y [ s i z e ] ; i n t s u b s i z e = s i z e / n t h r e a d s ; // Assume no r e m a i n d e r P a r t i a l D P dp [ n t h r e a d s ] ; f o r ( i n t i = 0 ; i < n t h r e a d s ; i ++){ dp [ i ]. s e t ( x, y, i * s u b s i z e, s u b s i z e ) ; t [ i ] = s t d : : t h r e a d ( dp [ i ] ) ; // Compute f o r ( i n t i = 0 ; i < n t h r e a d s ; i ++) t [ i ]. j o i n ( ) ; // A c cumulate t h e p r o d u c t double r e s u l t = 0 ; f o r ( i n t i = 0 ; i < n t h r e a d s ; i ++) r e s u l t += dp [ i ]. d o t p r o d u c t ;

16 Compiling C++11 With gcc, C++11 features can be compiled by using g++ -std=c++11 <args>