1. GETTING STARTED WITH C++ ID1218 Lecture 072009-11-18 Christian Schulte cschulte@kth.se Software and Computer Systems School of Information and Communication Technology KTH – Royal Institute of Technology Stockholm, Sweden

2. L07, 2009-11-18ID1218, Christian Schulte 2 Overview  C++ Basics Basic types and control structures  Functions and Arrays  Pointers  Some pragmatics…

3. L07, 2009-11-18ID1218, Christian Schulte 3 Goals  Familiarize with programming in C/C++  Understand underlying programming model  Understand language constructs program structure data structures and common algorithms memory management development pragmatics difference between C and C++  For later courses using C/C++

4. L07, 2009-11-18ID1218, Christian Schulte 4 Approach  Not from scratch, build Java as programming language  Efficient approach focus on essential not comprehensive apply practically

5. L07, 2009-11-18ID1218, Christian Schulte 5 Textbook  C++ for Java Programmers, Mark Allen Weiss, Prentice Hall, 2004 good selection of issues and topic non-naïve: no repetition what you know concise (very important) valuable resource after course!!!

6. L07, 2009-11-18ID1218, Christian Schulte 6 Other Valuable Books: C++  Thick, verbose, but useful J. Lajoie and S. Lippmann, C++ Primer 3 rd edition, Addison-Wesley, 1998.  Reference from the designer B. Stroustrup, The C++ Programming Language 3 rd edition, Addison-Wesley, 1997.  Tips for advanced issues R. B. Murray, C++ Strategies and Tactics Addison-Wesley, 1993.  C++ Standard library N. M. Josuttis, The C++ Standard Library Addison-Wesley, 1999.

7. L07, 2009-11-18ID1218, Christian Schulte 7 Other Valuable Books: C  The classic B. W. Kernighan and D. M. Ritchie, The C Programming Language 2 nd edition, Prentice Hall, 1997  Great reference, portability, also useful for C++ S. P. Harbinson, G. L. Steele, C – A Reference Manual 5 th edition, Prentice Hall, 2002

8. L07, 2009-11-18ID1218, Christian Schulte 8 What?  C++ as main vehicle basic issues pointers and references classes, objects, inheritance overview: operator overloading, templates, exceptions, input/output, standard library  Contrast with main differences in C basic issues (arrays) memory management, input/output mixing C and C++

9. L07, 2009-11-18ID1218, Christian Schulte 9 Why?  Study radically different model of computation not type safe: how to get along explicit memory management: no garbage collection, how to manage memory successfully close to abstraction level of machines  Ideally, do it in Erlang… …but can't be done take the trouble and use C++/C can be used afterwards anyway

10. L07, 2009-11-18ID1218, Christian Schulte 10 How?  Differential approach in contrast to Java: Java is close in many aspects  Practical approach try most important aspects in labs/tutorials

11. L07, 2009-11-18ID1218, Christian Schulte 11 What Do I Expect?  You will not become C++ wizards  You will understand the basic issues characteristics of computation model characteristics of development pragmatics  You will know where to look for further information language pragmatics

12. L07, 2009-11-18ID1218, Christian Schulte 12 Pragmatics  How to organize programming projects automatize recompilationmake  How to install software use configure  How to develop how to find errors: debugging how to improve performance: profiling

13. L07, 2009-11-18ID1218, Christian Schulte 13 Labs  Labs warm-up:introduction to pragmatics sound processing:to be handed in Sudoku solver:to be handed in Hand in: show to TA

14. L07, 2009-11-18ID1218, Christian Schulte 14 Reading Suggestions  All of you thorough reading of chapters 0 to 3 take a peek at chapter 11 do it, the book is a great read! go through the exercises!

15. Getting Started in C++ L07, 2009-11-18 15 ID1218, Christian Schulte

16. L07, 2009-11-18ID1218, Christian Schulte 16 Our First C++ Program #include using namespace std; int main() { cout << "Hello world." << endl; return 0; }

17. L07, 2009-11-18ID1218, Christian Schulte 17 Hello World Explained  Execution starts with main integer return value is error code (0 is okay) is normal function (a global function) functions in classes (methods): member functions can take additional arguments (command-line): later  All C++ programs are preprocessed #include resolved by preprocessor refers to C++ system IO #include "my.h" includes local file my.h Other uses: multiply used files (declarations, headers)

18. L07, 2009-11-18ID1218, Christian Schulte 18 Hello World Explained…  Standard functionality in namespace std becomes available by using namespace std; here: cout (standard output), endl (end of line)  Input similarly: int x; cout << "Your age: "; cin >> x; cin refers to standard input also common: using C-style input/output

19. L07, 2009-11-18ID1218, Christian Schulte 19 In Java… public class Hello { public static void main(String[]) { System.out.println("Hello world"); }

20. L07, 2009-11-18ID1218, Christian Schulte 20 Compiling and Running  Edit file emacs hello.cpp other extensions:.cc,.cxx,.C  Invoke compiler to create executable g++ hello.cpp –o hello.exe we use the GNU C++ compiler (g++)  Run executable./hello.exe

21. Basic Types and Control Structures L07, 2009-11-18 21 ID1218, Christian Schulte

22. L07, 2009-11-18ID1218, Christian Schulte 22 Primitive Types  Integer types  Floating point types  Character types  Boolean type  Non-primitive types arrays, objects, pointers, references, …

23. L07, 2009-11-18ID1218, Christian Schulte 23 Integer Types  Basic integer type int few guarantees on range in C++ today, often 32 bits, anytime soon 64 bits, … depends on machine (think of embedded…)  Can be augmented with short or long int never shorter than short int (at least 16) int never longer than long int (at least 32)  Can be modified with signed (default) or unsigned short signed int -32768 … 32767 short unsigned int 0 … 65535 just for example!

24. L07, 2009-11-18ID1218, Christian Schulte 24 Floating Point Types  Single precision float often: 32 bits  Double precision double often: 64 bits  Again, few guarantees

25. L07, 2009-11-18ID1218, Christian Schulte 25 Character Type  Character type char no guarantee on size, often 8 bits (ASCII, not Unicode!) unspecified whether signed or unsigned  Character constants in single quotes 'a', '1' escape sequences: '\n' for newline, etc  Also available: wchar_t for wide characters

26. L07, 2009-11-18ID1218, Christian Schulte 26 Boolean Type  Boolean type bool constants true and false  Rather late addition! watch out for int with zero as false and any other value true!

27. L07, 2009-11-18ID1218, Christian Schulte 27 Constants  Variables taking an immutable value cannot be changed abbreviation for commonly used values  Use const modifier const double pi = 3.1415; assignment to pi not possible

28. L07, 2009-11-18ID1218, Christian Schulte 28 Operators, Expressions, Statements  Almost the same in C++ as in Java in general: C++ carries some historic weight, Java has cleaned up, so watch out for some gotchas  Almost the same operators and expressions, conditionals, loops, … assignment: no guarantee of initialization  Additionally casts: change/convert/ignore type type definitions

29. L07, 2009-11-18ID1218, Christian Schulte 29 Operators and Expressions  No left to right order readInt() – readInt() with input 2 and 3 can be either 1 or -1  Integer division not guaranteed to round towards zero (book uses down) 8/-5 can be either -1 or -2  Comma operator: a,b evaluates to b weird things possible!

30. L07, 2009-11-18ID1218, Christian Schulte 30 Operators and Expressions  No guarantee on shift a << b can be either arithmetic or logic arithmetic -1 << 1 remains negative logic -1 << 1 is positive

31. L07, 2009-11-18ID1218, Christian Schulte 31 Conditionals  Condition can be either of type int or bool if (i) { … } else { … } If i is different from zero, take then part If i is zero, take else part not recommended, write if (i != 0) …  Common mistake if (x = 0) … actually meant: if (x == 0) … assigns 0 to x, takes the else part write variable to the right, if possible: if (0 == x)

32. L07, 2009-11-18ID1218, Christian Schulte 32 Loops  As in Java, along with break and continue

33. L07, 2009-11-18ID1218, Christian Schulte 33 Unitialized Variables  Variables not by guarantee initialized unless global or static (later)  Always give initial value important for objects (later)

34. L07, 2009-11-18ID1218, Christian Schulte 34 Typecasts for Primitive Types  Automatic conversion double x = 6.0; int y; y=x;  Typecasting can be essential int x=6; int y=10; double z = x/y; results in 0.0 rather than 0.6

35. L07, 2009-11-18ID1218, Christian Schulte 35 Static Casts  Cast at least one into double static_cast (x)/y;  Other casts dynamic_cast casting objects, later const_cast later reinterpret_cast just do it as size fits… C-style cast ((double) x) dangerous, combines everything, don't use!

36. L07, 2009-11-18ID1218, Christian Schulte 36 Type Definitions  Give names to types  Example: define implementation dependent integer type uint32 machine A: typedef unsigned long int uint32; machine B: typedef unsigned int uint32; rest of program can use uint32, does not require modification when being ported to machine C

37. Functions L07, 2009-11-18 37 ID1218, Christian Schulte

38. L07, 2009-11-18ID1218, Christian Schulte 38 Function Definition  Function definition contains return type function name parameter list body  Function can be called given function name and appropriate parameters  Function can only be defined once

39. L07, 2009-11-18ID1218, Christian Schulte 39 Function Example int maxx(int x, int y) { return (x > y) ? x : y; }

40. L07, 2009-11-18ID1218, Christian Schulte 40 Function Invocation  Print maximum of two numbers cout << maxx(43,27) << endl;  Uses call-by-value  Parameters need not be of type int automatic cast long int possibly with warning

41. L07, 2009-11-18ID1218, Christian Schulte 41 Function Overloading  The same function name can be used multiply with different types in parameter list double maxx(double x, double y) { return (x>y) ? x : y; }  Complicated set of rules describe which definition is chosen  Overloading with different return type only not allowed

42. L07, 2009-11-18ID1218, Christian Schulte 42 Function Declarations  Every function needs to be declared prior to invocation declared, but not defined! can be declared multiply  A function declaration is done by giving a function prototype int maxx(int, int); or int maxx(int a, int b);

43. L07, 2009-11-18ID1218, Christian Schulte 43 Default Parameters  Default values can be given for formal parameters if function has declaration, in declaration if function has only definition, in definition only allowed as last formal parameters  Assume that maxx is often used with 0 as second argument int maxx(int, int = 0); Then the following invocation is legal int z = maxx(-45); In this case, definition remains unchanged

44. L07, 2009-11-18ID1218, Christian Schulte 44 Inline Functions  Overhead of function call be significant: maxx is good example  Give function definition an inline directive inline int maxx(int x, int y) { … } Invocation of function is replaced by body Definition must be textually before first invocation  Compilers will also inline other, small functions

45. L07, 2009-11-18ID1218, Christian Schulte 45 Separate Compilation  Structure larger programs into separate files each file contains some functions: better structure each file can be compiled independently: save compilation time during development  Header file contains declarations and definitions of inline functions file name extensions:.h,.hh  Implementation file contains definition of functions (implementation)

46. L07, 2009-11-18ID1218, Christian Schulte 46 Header File maxx.h /* * Declaration of maximum function */ int maxx(int, int);

47. L07, 2009-11-18ID1218, Christian Schulte 47 Implementation File maxx.cpp #include "maxx.h" int maxx(int x, int y) { return (x > y) ? x : y; }

48. L07, 2009-11-18ID1218, Christian Schulte 48 Main File main.cpp #include #include "maxx.h" int main() { std::cout << maxx(47,23) << std::endl; return 0; }

49. L07, 2009-11-18ID1218, Christian Schulte 49 Putting Everything Together  Compile each implementation file independently g++ -c main.cpp g++ -c maxx.cpp creates the files main.o and maxx.o contain object code but require linking  Put everything together (linking) g++ main.o maxx.o –o main.exe

50. L07, 2009-11-18ID1218, Christian Schulte 50 Include Each Header at Most Once  Remember: inline functions must be defined not only declared before usage  Remember: at most one definition! what if header is included from other header files possibly having multiple definitions of same function also: why read same header more than once?  Use preprocessor (also macro processor) to guarantee at- most-once inclusion define a preprocessor variable when included test whether preprocessor variable not already defined choose reasonably unique name

51. L07, 2009-11-18ID1218, Christian Schulte 51 Fixed Header File maxx.h /* * Declaration of maximum function */ #ifndef __MAXX_H__ #define __MAXX_H__ int maxx(int, int); #endif

52. L07, 2009-11-18ID1218, Christian Schulte 52 Organizing Compilation  How to organize compilation recompilation needed if included header file changes compilation can be time-consuming: > 1000 files? only recompile what is needed  Use make: express dependencies among files files only recompiled, if dependencies change rules for how to perform compilation.cpp .o.o .exe later (first lab session) more

53. Arrays L07, 2009-11-18 53 ID1218, Christian Schulte

54. L07, 2009-11-18ID1218, Christian Schulte 54 C-style Arrays  C-style arrays int a[42]; creates an array of 42 integers access cout << a[1]; assignment a[1] = a[2]+a[3]; ranges from a[0] to a[41]  Dimension of array must be constant can be evaluated at compile time to constant (eg 2*4 ) illegal int a[n] where n is variable!

55. L07, 2009-11-18ID1218, Christian Schulte 55 Using Arrays as Parameters int find_max(int a[], int n) { int m = a[0]; for (int i = 1; i<n; i++) if (a[i] > m) m=a[i]; return m; }  Array of arbitrary size int a[] requires to pass size as extra parameter int n

56. L07, 2009-11-18ID1218, Christian Schulte 56 Using Arrays as Parameters int find_max(int a[42]) { int m = a[0]; for (int i = 1; i<42; i++) if (a[i] > m) m=a[i]; return m; }  Supports only arrays statically known to have size 42!

57. L07, 2009-11-18ID1218, Christian Schulte 57 Allocating Arrays  What if size is not known statically memory for array must be allocated from heap after use, memory must be explicitly freed  C++ style memory management use new [] and delete [] special versions for arrays normal versions to be used later for objects

58. L07, 2009-11-18ID1218, Christian Schulte 58 Allocating Arrays  Allocate an array of integers with size n new int[n];  Free memory array (no matter its size or type) delete [] a;  The following does not work int a[] = new int[n]; a must have know size, or used as parameter use pointers rather than arrays (a little later)

59. L07, 2009-11-18ID1218, Christian Schulte 59 Primitive Arrays of Constants  Initialize arrays in declaration declare array to be not assignable const int DIM[] = {31,28,31,30,31,30, 31,31,30,31,30,31}; declares array of size 12

60. L07, 2009-11-18ID1218, Christian Schulte 60 C-Style Strings  Use arrays of chars!  Often const char s[] = "A C-string."; contains all letters given plus 0 at the end (end-of-string marker) has size 12 (additional 0)

61. L07, 2009-11-18ID1218, Christian Schulte 61 Vectors and C++ Strings  Vectors are C++ arrays #include automatic resize automatic memory management copied when passed as parameters  Strings #include same advantages as above support for comparison, copying on assignment, …  Please read book about both vectors and strings

62. Parameter Passing L07, 2009-11-18 62 ID1218, Christian Schulte

63. L07, 2009-11-18ID1218, Christian Schulte 63 Call By-value  Default mechanism already seen works by copying: straightforward for primitive types but copying also for objects: to be discussed later!  What if one return value is not enough? use call by-reference

64. L07, 2009-11-18ID1218, Christian Schulte 64 Call By-reference  Function to exchange to values, first attempt (wrong): void exc(int a, int b) { int t=a; a=b; b=t; } just works on copies passed to exc need to pass references instead

65. L07, 2009-11-18ID1218, Christian Schulte 65 Call By-reference  Function to exchange to values (correct): void exc(int &a, int &b) { int t=a; a=b; b=t; } a and b are passed by reference effect is on actual parameters int x = 4; int y = 5; exc(x,y); constants are not allowed as actual parameters exc(x,5);

66. Pointers: Outlook L07, 2009-11-18 66 ID1218, Christian Schulte

67. L07, 2009-11-18ID1218, Christian Schulte 67 Pointers  Are a consequence that memory management is not abstracted away Erlang and Java: all variables hold references to values, operations are performed implicitly on value  C and C++ distinguish objects (also primitive values) pointers: values which point to memory address of objects

68. L07, 2009-11-18ID1218, Christian Schulte 68 Pointers  Declaring a pointer to an integer int* p;  Let p point to address of x int x = 5; p = &x; & is called unary address-of operator  Read value at pointer: prints 5 cout << *p; * is called unary dereference operator  Store value at memory referenced at p: prints 7 *p = 7; cout << x;

69. L07, 2009-11-18ID1218, Christian Schulte 69 Pointers Illustrated…  After declaration int x = 10; int y = 7; int* p; p points somewhere (unitialized) (&x) 100 x = 10 (&y) 104 y = 7…… (&p) 200 p = ????…

70. L07, 2009-11-18ID1218, Christian Schulte 70 Segmentation Fault or Bus Error…  Assign object pointed to by p a value *p = 124; but: not necessarily, p can also point to some other location (overrides other variables contents…) (&x) 100 x = 10 (&y) 104 y = 7…… (&p) 200 p = ????…

71. L07, 2009-11-18ID1218, Christian Schulte 71 Redirecting…  Let p point to location of x p = &x; (&x) 100 x = 10 (&y) 104 y = 7…… (&p) 200 p = &x = 100…

72. L07, 2009-11-18ID1218, Christian Schulte 72 Assigning…  Assign object pointed to by p a value *p = 5; (&x) 100 x = 5 (&y) 104 y = 7…… (&p) 200 p = &x = 100…

73. L07, 2009-11-18ID1218, Christian Schulte 73 Redirecting…  Let p point to location of y p = &y; (&x) 100 x = 5 (&y) 104 y = 7…… (&p) 200 p = &y = 104…

74. L07, 2009-11-18ID1218, Christian Schulte 74 Assigning…  Assign object pointed to by p a value *p = 99; (&x) 100 x = 5 (&y) 104 y = 99…… (&p) 200 p = &y = 104…

75. L07, 2009-11-18ID1218, Christian Schulte 75 Common Idioms  Testing that pointers refer to same location p1 == p2  Testing that objects pointed to have same value *p1 == *p2  Use NULL for ptr not pointing anywhere const int NULL = 0; use in initialization, tests, etc

76. L07, 2009-11-18ID1218, Christian Schulte 76 Heap Memory Management  Get memory from heap int* p = new int; allocate memory block big enough for one int  After use, release delete p;

77. L07, 2009-11-18ID1218, Christian Schulte 77 Getting It Wrong  Forget to delete program crashes when running out of memory  Delete to early lucky case: program crashes due to OS knowing that memory has been freed unlucky case: already reused, arbitrary things can happen!  Delete twice runtime error

78. L07, 2009-11-18ID1218, Christian Schulte 78 What Is Next?  Storage classes automatic and static variables  Arrays are pointers int* a = new int[n];

79. Summary L07, 2009-11-18 79 ID1218, Christian Schulte

80. L07, 2009-11-18ID1218, Christian Schulte 80 Summary  Radically new computation model not type safe explicit memory management  Few guarantees primitive types and their operations  Memory management is very difficult!