Some other issues in C++

1. Some other issues in C++ 蔡文能 tsaiwn@csie.nctu.edu.tw tsaiwn@cs.nctu.edu.tw 交通大學資訊工程學系 2006/08/23 交通大學資訓工程學系 蔡文能

2. http://tsaiwn.net/cpp/ Agenda http://www.csie.nctu.edu.tw/~tsaiwn/cpp • Namespace • static ? • const ? • cast in C++ • C++ Class Library • STL – Standard Template Library • Exception handling 交通大學資訓工程學系 蔡文能

3. Namespaces • variables with same name and different scopes can overlap • need to distinguish them • a namespace defines a scope for local and global identifiers. • body delimited by braces {} • use (::) to access namespace members: namespace_name::member • or, a using statement must occur before name is used using namespace namespace_name; -members of thenamespace do not need a prefix • not guaranteed to be unique • can be nested 例如 std::cout • using namespace std; //for STL 交通大學資訓工程學系 蔡文能

4. 神奇的 “static” • On a global variable or a function static long myData[38]; //information hiding static void myFunction(float); • Tells the linker not to export the variable or function. • Makes the identifier “file scope,” as the linker will not use it fulfill dependencies from other files. • On a local variable in a function void someFunc(void) { static int array[4000]; } Places the variable off the stack. This has the side-effect that it retains it value across calls. It is often used when a variable is too large to be put on the stack. (auto變數則在 stack) • On a class member data or member function (next slide) 交通大學資訓工程學系 蔡文能

5. Static Global 變數 參考K&R課本4.6節 #include <stdio.h> #define BUFSIZE 100 static char buf[BUFSIZE]; int bufp = 0; int getch( ) { /* . . . */ } void ungetch(int c) { /* . . . */ } 別的檔案中任何function都看不見這個 static 的變數 也參考stack的push和pop寫在同一獨立 file 中, push和pop共享 data 交通大學資訓工程學系 蔡文能

6. 再談Static Global 變數 參考K&R課本4.6節 #include <stdio.h> #define RAND_MAX 65535 static unsigned long seed=0; int rand( ) { seed = seed * 1103515245 + 12345; return seed % (RAND_MAX+1); } void srand(int newseed) { seed = newseed; } Pseudo random number 交通大學資訓工程學系 蔡文能

7. (1/2) Static Local變數 #include <iostream.h> int fa( ) { int x = 1; return x++; /*先取其值, 再做 ++ */ } int fb( ) {static int x = 1; /*注意 static int x = 1; */ return x++; } int main( ) { cout << "fa( )=" << fa( )<<fa( )<<fa( ) << endl; cout << "fb( )=" << fb( )<<fb( )<<fb( ) << endl; return 0; /* 0 in main( ) means OK */ } return x++; 和return ++x;不同! 交通大學資訓工程學系 蔡文能

8. (2/2) Static Local變數 int fa( ) { int x = 1; return x++; /*先取其值, 再做 ++ */ } int fb( ) { static // 把 static 寫在下列左方也一樣 int x = 1; // 注意 static int x = 1; return x++; } 交通大學資訓工程學系 蔡文能

9. Static Local變數 , evaluation 順序 #include <stdio.h> int fa( ); /*宣告*/ int fb( ); int main( ) { /* 不同系統可能不同答案*/ printf( "fa( )=%d %d %d \n", fa( ), fa( ), fa( ) ); printf( "fb( )=%d %d %d \n", fb( ), fb( ), fb( ) ); return 0; /* 0 in main( ) means OK */ } // int fa( ) … 也可以寫在另一個檔案內 交通大學資訓工程學系 蔡文能

10. Static class member • static member不需要透過任何的object存取，在無任何object時可透過member selection operators (就是 ::或Java仍用 . )來存取. • Static member functions • Also known as class function(class methods) • Can be called without any instance, for example: m = Mankind::howmany( ); • Can NOT access instance variables • Static member data • Also known as class variable • All objects of a class share one copy of a static data member (non-static member data = instance variable) • Usage example: x = Mankind::data_which_is_static; • They are not global variables; they have class scope • All member functions are shared between objects, even the non-static member functions 交通大學資訓工程學系 蔡文能

11. 神奇的 “const” • Const object isNOT modifiable • const x = 3.14159; // 在 C 與較舊C++ compile會過;問題在哪裡? • Const parameter can NOT be modified in the function ReturnType FunctionName(long x, const Student y){ /*… to modify y is NOT allowed! 即 y 不可當左值 */ }; • Const member function can NOT modify the object ReturnType FunctionName(param1,param2…)const; ReturnType FunctionName(param1,param2…)const{ /*… */}; • Constructors / Destructors cannot be const • They need to initialize variables (therefore modifying them) const 是不准變的變數! 也佔一塊記憶體! 那 #define nsize 99呢? 交通大學資訓工程學系 蔡文能

12. Review: Constants 常數 • #define MAX_LOOP 500 • 此稱 define macro 巨集 • 是C的前處理器之句子, 結尾不必有分號 • 之後用到 MAX_LOOP 會被換成 500 • const double delta = 0.0001; ^^^^^^^^^^^^^^^^ 不可變的變數叫const • const PI = 3.14159;/* Error result? PI為 3*/ 交通大學資訓工程學系 蔡文能

13. Character Literal • 單引號夾住是 char • 'A' 相當於 65 (assume using ASCII) • 'a' 相當於 97 (assume using ASCII) • '0' 相當於 48 (assume using ASCII) • Wide character ? • Escape Sequence 逃脫序列串 • '\n' == '\012 ' • '\101' == 'A' • '\x41' == 'A' 交通大學資訓工程學系 蔡文能

14. Escape Sequence 逃脫序列串 • '\a' == '\007' == CTRL_G == Alert (Bell) • '\b' == '\010' == CTRL_H == BackSpace • '\f' == '\014' == CTRL_L == FormFeed • '\n' == '\012' == CTRL_J == NewLine • '\r' == '\015' == CTRL_M == Carriage RETURN • '\t' == '\011' == CTRL_I == TAB (Horizontal Tab) • '\v' == == Vertical Tab • ' \\' == == backslash 反斜線 • '\?' == == question mark • '\' ' == == single quote ( apostrophe ) • '\" ' == == double quote (quote) '\060' '\x30' 參考K&R課本2.3節 交通大學資訓工程學系 蔡文能

15. Cast in C++ • C++ has 4 more separate, specific casts • Conventional static cast (C-Style): (type)expression • static_cast - conversion between types • type checking at compile time • standard conversions: void* to char*, int to float, etc. • base class pointers to derived class pointers • Format: static_cast<type to convert to>(object to convert) • const_cast - cast away const or volatile • cannot be used directly to cast away const-ness; use pointers • dynamic_cast – for safe navigationof an inheritance hierarchy. • Can be used only for pointer or reference types • reinterpret_cast - for nonstandard casts • one pointer type to another pointer type, void* to int*, etc. • cannot be used for standard casts (int to double, etc.). 交通大學資訓工程學系 蔡文能

16. C ++ class Library <algorithm> <bitset> <complex> <deque> <exception> <fstream> <functional> <iomanip> <ios> <iosfwd> <iostream> <istream> <iterator> <list> <locate> <limits> <map> <memory> <new> <numeric> <ostream> <queue> <streambuf> <string> <set> <sstream> <stack> <stdexcept> <typeinfo> <utility> <valarray> <vector> <cmath> 交通大學資訓工程學系 蔡文能

17. C++ classes for I/O 交通大學資訓工程學系 蔡文能

18. 再談 C Language 程式庫 • 程式庫裡除了 sqrt (double); 之外, 還有許多常用的函數(函式), 有許多其實都很簡單 • printf, scanf, getchar, fopen, … 這些與 I/O有關的函數被宣告在 stdio.h, 所以要在程式中 #include<stdio.h> 用 < > 夾起來表示在系統某個目錄之下, 例如/usr/include/ • 所有 Library function 參看 K&R 附錄B 交通大學資訓工程學系 蔡文能

19. Standard C Library <stdio.h> <math.h> <stdlib.h> <string.h> <ctype.h> <time.h> <assert.h> <float.h> <limits.h> <stdarg.h> <stddef.h> <errno.h> <locale.h> <signal.h> <setjmp.h> • open, read, write, close 等不是 standard C Library, 而是 system call • C Library 在 UNIX 手冊第三章, System call 在 UNIX 手冊 第二章( 用 man 會看到 (2) ) • 所有 Library function 參看 K&R 附錄B 交通大學資訓工程學系 蔡文能

20. The C++ String Class • The C-style strings (arrays of char) that you’ve been using are not the only way of managing character data. • C++ allows you to work with a string class that eases many of the problems you’ve encountered with C-style strings. • In particular, you don’t have to worry about managing memory for the string data. 交通大學資訓工程學系 蔡文能

21. C++ String Basics • The basic character template class is basic_string<>. • It has two specializations (generated using typedefs), string and wstring. • string corresponds to the C-style string (I.e., const *char). • wstring is an extension for languages that use characters. • You can copy, assign, and compare strings just like you would copy, assign, and compare primitive types (int, double) string a = “Hello”; string b = string(a); string c = a; bool d = (a==b); 交通大學資訓工程學系 蔡文能

22. using the String types • In the header file <string> • (Note, no .h) • All such functions and other names are in the namespace std. • The basic class name is a template class, basic_string<>. • String constructors string( ) // empty string(string s) // copy of s string(string s, int start) // substring string(string s, int start, int len) // substring string(char* a) // C-string string(int cnt, char c) // one or more chars string(char* beg, char* end) // [beg, end) 交通大學資訓工程學系 蔡文能

23. Accessing Individual Characters • It’s almost like for a C-string. string s = “Harry”; s[0] is ‘H’ s[1] is ‘a’ … s[5] is undefined!!!! – no ‘\0’ at the end 交通大學資訓工程學系 蔡文能

24. C++ string Operations • = is used to assign a value (char, C-string, or string) to a string. • += is used to append a string, character, or C-string to a string. • + is used to concatenate two strings or a string with something else • Boolean operations do a dictionary order comparison • << and >> are used for input and output. On input, leading whitespace is skipped, and the input terminates with whitespace or end of file. 交通大學資訓工程學系 蔡文能

25. Other C++ string Operations swap(a, b); // swap the guts of a with b s.append(s2); // append s2 to s s.c_str( ); // return a C-string s.push_back(c); // append a char s.erase(various); // erases substrings s.insert(various); // inserts substrings s.clear(); // removes all contents s.resize(cnt); // change the size of s to cnt s.replace(various); // replaces characters s.size(); // how many characters? s.length(); // how many characters? s.max_size(); // maximum number of char? s.empty(); // is s empty? s.capacity(); // size without reallocation s.reserve(cnt); // reserves memory 交通大學資訓工程學系 蔡文能

26. Using c++ string string s = "Harry "; s.data() // returns s as a data array, no '\0' . s.c_str() // returns s as a C-stringwith '\0' int i = atoi(s.c_str()); // conversion char *carray = new char[80]; s.copy(carray, 79); // copies up to 79 char 交通大學資訓工程學系 蔡文能

27. STL Algorithms - <algorithm> • binary_search • sort • count: count(list.begin(), list:end(), val, num); • equal: compares containers • for_each: applies ftn to each element • copy: copies container • reverse • min/max • Some in <numeric> 交通大學資訓工程學系 蔡文能

28. Vectors again 交通大學資訓工程學系 蔡文能

29. Using vector vector <int> v; v.reserve (100); // allocate space for 100 integers // capacity 100, size 0 int i; while (cin >> i) // read from the standard input v.push_back (i);// will expand v if needed for (i = 0; i < v.size (); ++i) cout << v[i]; try { // use checked access cout << v.at (100); // may throw } catch (std::out_of_range&) { cout << "doesn't have 101 elements" << endl; } for (int i = 0; i < v.size () / 2; ++i) v.pop_back ();// remove second half vector <int> v1 (v); // copy to v1 v1.insert (v1.begin ()+1, 117); // insert after first 交通大學資訓工程學系 蔡文能

30. Utilities: pair • a helper class template std::pair, used a lot by the standard library template <typename T1, typename T2> // simplified struct pair { T1 first; T2 second; pair () : first (T1()), second (T2()) {} // init pair (const T1&, const T2&); ... // etc. }; • provides a full range of comparison operations:==,<, etc. • a related helper function template to make pairs: std:pair <int, double> w = std::make_pair (1, 1.2); 交通大學資訓工程學系 蔡文能

31. Sequences • There are several kinds of sequences; choose • vectors when • there are random access operations, • most insertions and removals are at the end of the container • deques when • there are frequent insertions and deletions at either end, • there are random access operations • lists when • there are frequent insertions and deletions at positions other than at the end • there are few random access operations • want to guarantee iterators are valid after modifications 交通大學資訓工程學系 蔡文能

32. Deques • deques are similar to vectors • deque iterators are random access • additionally two operations to insert/remove elements in front: push_front () add new first element pop_front () remove the first element • deques do not have operations capacity () and reserve() 交通大學資訓工程學系 蔡文能

33. Linked Lists list <char> s; // empty list s.insert (s.end (), 'a'); s.insert (s.end (), 'b') // s has (a, b) list <char> s1; // empty list // copy sto s1: s1.insert (s1.end (), s.begin (), s.end ()); s.clear (); cout << s1.front (); s1.erase (s1.begin ()); // remove first element 交通大學資訓工程學系 蔡文能

34. Linked Lists (cont.) 交通大學資訓工程學系 蔡文能

35. Iterators again • an iterator provides access to objects stored in a container (points to an element); every iterator it has to support: *itto access the element currently pointed to by the iterator ++it to move to the next element of the container it == it1 to compare two iterators for pointer equality it != it1to compare two iterators for pointer inequality • every container type provides one or more iterators in a uniform way as standardized type names: std::vector <string>::iterator std::vector <string>::const_iterator begin ()returns an iterator pointing to the first element end () returns an iterator pointing past the end; serves as a sentinel, i.e., end marker. 交通大學資訓工程學系 蔡文能

36. Iterators again (cont.) • the iterator operations are sufficient for iterating over any Container: Container c; ... Container::iterator it; for (it = c.begin (); it != c.end (); ++it) { .. *it .. it->op () .. } • a sequence of consecutive values in the container is determined by an iterator range, defined by two iterators, [first, last) • last is assumed reachable from first by using the ++ operator, and all iterators, including first but excluding last can be dereferenced • two iterators can be compared for equality and inequality 交通大學資訓工程學系 蔡文能

37. Associative Containers • STL associative containers: • represent sorted collections • have keys, and are sorted on these keys • A map is a mapping from keys to values: • it stores pairs (key, value) • there may be at most one pair with the same key • e.g.: (123, "Bush")and (124, "Kerry") • A multimap: • may have more than one pair with the same key • e.g., (123, "Bush") and (123, "Kerry") 交通大學資訓工程學系 蔡文能

38. map usage // map: string to doubles map <string, double> salaries; // map: string to doubles sorted by greater <string> map <string, double, greater <string> > salaries1; • to access an element of a map, you can use an overloaded index operatoroperator [](key): salaries1 ["John"] = 10000; salaries1 ["Mary"] = 20000; • operator[] can not be used for multimaps; for example multimap <string, string> mm; mm ["color"] = "blue"; // compile-time error • instead, you have to useinsert (): mm.insert ("color", "blue"); mm.insert ("color", "green"); 交通大學資訓工程學系 蔡文能

39. STL e.g.: using map • Goal: store grades for group of students • ordered set of assignments • maybe students with same name • For each student, have grades • want fast access to each grade • use vector of chars • typedef vector<int> Grades; • First, create map of students: • map<string, Grades> roster; 交通大學資訓工程學系 蔡文能

40. Using map: add a student to map • map represents a function: key maps to value • map, basically: set of ordered pairs • pair<x,y> template • void Roster::addStudent(const string &name) { //check if already exists if (roster.find(name) != roster.end()) return; //check for room if (roster.size() == MAX) waitList.push_back(name); else { Grades grades; roster.insert( pair<string,Grades>(name,grades)); } 交通大學資訓工程學系 蔡文能

41. Using map: drop a student • void Roster::dropStudent(String &name) { if (roster.find(name) == roster.end()) return; roster.erase(name); if (waitList.size() > 0) { string wait = waitList.pop_front(); waitList.pop(); Grades grades; roster.insert( pair<string,Grades>(name,grades)); } } 交通大學資訓工程學系 蔡文能

42. Using map: set a grade • void Roster::setGrade(const &string name, const int assign, const char grade) { map<string,Grades> stud = roster.find(name); if (stud == roster.end()) { cerr << “not found\n”; return; } if (stud->second().size() <= assign) stud->second().resize(assign+1); stud->second[assign] = grade; } 交通大學資訓工程學系 蔡文能

43. Associative Containers (cont.) • set is a map for which the key and the value are identical - therefore it stores logically single elements rather than pairs • multisets are sometimes called bags; they are like sets except there may be more than one occurrence of an element with the same key • elements in associative containers are sorted by the value of a key • associative containers use a binary predicate less<Key>, which compares two Key elements, using Key::operator<. • thelesspredicate also determines the meaning of two keys being equivalent: two keys of an associative container are equivalent if neither is less than the other 交通大學資訓工程學系 蔡文能

44. Container Traits 交通大學資訓工程學系 蔡文能

45. Container Operations 交通大學資訓工程學系 蔡文能

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49. http://www.csie.nctu.edu.tw/~tsaiwn/cpp/ Thank You! 謝謝捧場 tsaiwn@csie.nctu.edu.tw 蔡文能 交通大學資訓工程學系 蔡文能