Stream io C default io class C stream

Stream i/o C++ default i/o class

C++ stream i/o classes Template class character based class wide-character based class basic_ios wios basic_istream wistream basic_ostream wostream basic_iostream wiostream basic_fstream wfstream basic_ifstream wifstream basic_ofstream wofstream

Predefined stream objects cin standard input keyboard cout standard output monitor cerr standard error output monitor clog Buffered version of cerr monitor When a C++ program being execution, four built-in streams are automatically opend, corresponding to stdin, stdout, stderr in C.

Using stream i/o #include <iostream> using namespace std; int main() { int a = 2; float b = 3. 4; double c = 2. 717281828; char d = ‘t’, str[10]=“This is a string”; cout << a << b << c << d << str << endl; cout << "type c : " ; cin >> c; cout << "type a string : " ; cin >> str; cout << c << " " << str << endl; system("pause"); example } return 0;

cin -- an object of class basic_istream<char> cout -- an object of class basic_ostream<char> >> , << 為 class 的 operator>>, operator<<. cout << a; 也可以寫成 cout. operator<<(a); cin >> b; 也可以寫成 cin. operator>>(b); 在以 function overload 的方式處理不同 type 的 a 和 b. To format the stream i/o 1. Using format flags (members of basic_ios<char> class) 2. Member functions in iostream classes. 3. Using member functions in iomanip classes.

Set i/o flag in basic_ios adjustfield hex showbasefield internal showpoint boolalpha left showpos dec oct skipws fixed right unitbuf floatfield scientific uppercase Syntax: Set flags: cout. setf( ios: : flag 1 | ios: : flag 2 | ios: : flag 1, ios: : flag 2); Clear flags: cout. unsetf( ios: : flag 1 | ios: : flag 2 | ios: : flag 1, ios: : flag 2);

example int a = 100; double c = 2. 717; cout. setf(ios: : hex, ios: : basefield); cout << a << endl; // 64 cout. setf(ios: : showbase); cout << a << endl; // 0 x 64 cout. setf(ios: : uppercase | ios: : scientific); cout << c << endl; // 2. 717 E+000 cout. setf(ios: : showpos); cout << c << endl; // +2. 717 E+000 cout. unsetf(ios: : showpos | ios: : uppercase); cout << c << endl; // 2. 717 e+000

格式控制 (三) Manupilator #include <iomanip> left endl dec fixed showpos skipws internal right ends hex scientific noshowpos noskipws boolalpha cout cout << << << setw(n) flush oct showpoint setprecision(n) setfill(char) uppercase nouppercase showbase noshowpoint setiosflags(ios: : floag) (cin) noboolalpha unitbuf setprecision(10) << a << endl; setw(30) << a << endl; setfill('-'); left << setw(30) << a << endl; setw(30) << b << " "; setw(30) << c << endl; nounitbuf example

Overload cout << (binary operator) ostream &operator<< (ostream &stream, class_type object) { stream << object. member; . . return stream; } 1. 2. 3. 4. 5. Operator<< 必須宣告為 passed by reference Ostream 為一 basic_ios <char> 的 class. 第一個幅數 cout 也必須宣告為 pass by reference (連接到 stdout). 第二個幅數是要被列印的 class 物件. 若列印的內容有需要用到 class 的 protected member 必須將 << 宣告為 class 的 friend: friend ostream &operator<< (ostream &, class_type);

Overload cin >> (binary operator) istream &operator>> (istream &stream, class_type &object) { cout << “type member 1 : “; stream >> object. member 1; . . return stream; } 1. 2. 3. 4. 5. Operator>> 必須宣告為 passed by reference istream 為一 basic_ios <char> 的 class. 第一個幅數 cin 也必須宣告為 pass by reference (連接到 stdin). 第二個幅數是要被存放的 class 物件, 也必須 pass by reference. 若存放過程有需要用到 class 的 protected member 必須將 >> 宣告為 class 的 friend: friend istream &operator>> (istream &, class_type &);

練習. . 主程式範例 1 主程式範例 2 請寫 position class 的 cin >> 和 cout << 的 overload operators. position r 1, r 2; cin >> r 1; cin >> r 2; cout << (r 1*r 2) << endl; cout << (r 1+r 2) << endl; 並思考如何控制 cout 的格式: 因為 ostream operator<< 是寫 在 class 定義檔中 (假想你是 developer, 並不希望 programmer 去更動 class 的 code. ) 所以必須在 class 內加添一些 member 變數用以控制 cout 的格式 (e. g. width), 並加入適當的 member functions 讓 programmer 可以從外面改變格式參數. 請注意在 class 的 constructors 中也要 initial 此參數之值.

Text File stream Input text from a file: Output text to a file: #include <fstream> main() {. . . ; ifstream inf(“file_name”); main() {. . . ; ofstream outf(“file_name”); inf >> a >> b >> c; outf << a << b << c; for (i=0; i<10; i++) outf << aary[i]; for (i=0; i<10; i++) inf >> aary[i]; } inf. close(); . . . ; } outf. close(); . . . ;