CSCI 333 Data Structures

1. CSCI 333Data Structures I/O with C++ 20 October, 2003

2. C++ Stream I/O hierarchy fstream ifstream ofstream multiple inheritance iostream istream ostream virtual base class virtual base class ios

3. ios class • Formatting • Width of field, base of numbers • State • Open, closed, end-of-file, failed • Constants • Open for read/write/append • Buffering • Usingstreambufclass

4. ANSI C++ios • To support internationalization • iosis a template of • basic_ios • Specialized for character set • But western programmers don’t worry • Except when looking at the documentation

5. ios flags for opening files

6. ios state methods

7. ios formatting methods

8. iosflags for moving in files

9. istream class • Stream input class • Read from files • to all sorts of variables • Seek to arbitrary file position • Templated in ANSI C++ • from basic_istream

10. Some istream methods

11. Some ostream methods

12. The iostream methods • Multiple inheritence • istream • ostream • Single ios subclass • Since ios is a virtual subclass

13. The standard streams

14. The fstream methods • Most inherited from *stream methods • fstream F ; • fstream F(filename, flags) ; • F.open(filename, flags) ; • F.close() ;

15. // Opening and closing with ifstream and ofstream #include <fstream> using namespace std ; int main(int argc, char *argv[]) { ifstream RStream ; ofstream WStream ; RStream.open(argv[1]) ; if (RStream.bad()) cerr << "Unable to read " << argv[1] << endl ; RStream.close() ; WStream.open(argv[1]) ; if (WStream.bad()) cerr << "Unable to write " << argv[1] << endl ; WStream.close() ; }

16. // Opening and closing with fstream #include <fstream> using namespace std ; int main(int argc, char *argv[]) { fstream RWStream ; RWStream.open(argv[1], ios::in) ; if (RWStream.bad()) cerr << "Unable to read " << argv[1] << endl ; RWStream.close() ; RWStream.open(argv[1], ios::out) ; if (RWStream.bad()) cerr << "Unable to write " << argv[1] << endl ; RWStream.close() ; }

17. // Silly file updates #include <fstream> using namespace std ; int main(int argc, char *argv[]) { fstream RWStream ; RWStream.open(argv[1], ios::in | ios::out | ios::binary) ; if (RWStream.bad()) cerr << "Unable to read or write" << argv[1] << endl ; else { char buff[7] ; // Read from characters 7 to 13 RWStream.seekg(7, ios::beg) ; RWStream.read(buff, 7) ; // Write to characters 14 to 20 RWStream.seekp(14, ios::beg) ; RWStream.write(buff, 7) ; RWStream.close() ; } }

18. // Reverse a file #include <fstream> using namespace std ; int main(int argc, char *argv[]) { fstream RWStream ; RWStream.open(argv[1], ios::in | ios::out | ios::binary) ; if (RWStream.bad()) cerr << "Unable to read or write" << argv[1] << endl ; else { char buffFront[1] ; // extremely inefficient char buffRear[1] ; RWStream.seekp(0, ios::end) ; int fileSize = RWStream.tellp() ; for (int i=0; i<fileSize/2; ++i) { RWStream.seekg(i, ios::beg) ; RWStream.read(buffFront, 1) ; RWStream.seekg(fileSize-i-1, ios::beg) ; RWStream.read(buffRear, 1) ; RWStream.seekp(i, ios::beg) ; RWStream.write(buffRear, 1) ; RWStream.seekp(fileSize-i-1, ios::beg) ; RWStream.write(buffFront, 1) ; } } RWStream.close() ; }

19. // writing numbers in ASCII and binary #include <fstream> using namespace std ; int main(int argc, char *argv[]) { ofstream WStream ; WStream.open(argv[1], ios::binary) ; if (WStream.bad()) cerr << "Unable to write" << argv[1] << endl ; else { for (int i=333; i<343; ++i) WStream << i ; for (int i=333; i<343; ++i) WStream.write((char *)&i, sizeof(i)) ; } WStream.close() ; }

20. // formatted I/O with ios methods #include <iostream> using namespace std ; int main(int argc, char *argv[]) { cout.fill('0') ; for (int i=0; i<100; ++i) { cout.width(2) ; cout << i ; cout.width(4) ; cout << i*i << endl ; } }

21. // formatting with io manipulators #include <iostream> #include <iomanip> using namespace std ; int main(int argc, char *argv[]) { cout.fill('0') ; for (int i=0; i<100; ++i) cout << setw(2) << i << " " << setw(4) << i*i << endl ; }

22. // Reading integers or characters #include <iostream> using namespace std ; int main(int argc, char *argv[]) { int i ; cin >> i ; if (cin.fail()) { cin.clear() ; char c ; cin >> c ; if (cin.fail()) cout << "Failure on I/O" ; else cout << "Read character '" << c << "'" << endl ; } else cout << "Read integer " << i << endl ; }

23. // Summing integers #include <iostream> using namespace std ; int main(int argc, char *argv[]) { int i ; int sum = 0 ; while(cin >> i && cin.good()) sum += i ; cout << "Total = " << sum << endl ; }

24. #include <iostream> #include <sstream> using namespace std ; #define INBUFFSIZE 4096 int main(int argc, char *argv[]) { int sum = 0 ; char inLine[INBUFFSIZE+1] ; while (cin.getline(inLine, INBUFFSIZE) && cin.gcount()) { int lineSum = 0 ; int i ; istringstream lineStream(inLine) ; while (lineStream>>i && lineStream.good()) lineSum += i ; if (lineStream.eof()) sum += lineSum ; else cerr << "Ignoring bad input line: " << inLine << endl ; } cout << "Sum = " << sum << endl; }