Streams, Files, and Formatting

1. Streams, Files, and Formatting Chapter 8

2. 8.1 Standard Input/Output Streams • Stream is a sequence of characters • Working with cin and cout • Streams convert internal representations to character streams • >> input operator (extractor) • << output operator (inserter) • Streams have no fixed size

3. Reading Data >> • Leading white space skipped • <nwln> also skipped • Until first character is located cin >> ch; • Also read character plus white space as a character • get and put functions

4. CountChars.cpp // File: CountChars.cpp // Counts the number of characters and lines in // a file #include <iostream> #include <string> using namespace std; #define ENDFILE "CTRL-D" // CTRL-Z for DOS

5. CountChars.cpp int main() { const char NWLN = '\n'; // newline character char next; int charCount; int totalChars; int lineCount; lineCount = 0; totalChars = 0;

6. CountChars.cpp cout << "Enter a line or press " << ENDFILE << ": "; while (cin.get(next)) { charCount = 0; while (next != NWLN && !cin.eof()) { cout.put(next); charCount++; totalChars++; cin.get(next); } // end inner while

7. CountChars.cpp cout.put(NWLN); lineCount++; cout << "Number of characters in line " << lineCount << " is " << charCount << endl; cout << "Enter a line or press " << ENDFILE << ": "; } // end outer while cout << endl << endl << "Number of lines processed is " << lineCount << endl;

8. CountChars.cpp cout << "Total number of characters is " << totalChars << endl; return 0; } Example of a user session: Enter a line or press CTRL-D: line one. Line one. Number of characters is 9 Enter a line or press CTRL-D: line four. Line four. Number of characters is 10 Enter a line or press CTRL-D: CTRL-D Number of lines processed is 2 Total number of characters is 19

9. Stream Functions • stream.open(fname): opens a file stream • stream.get(ch): extracts one character from stream • stream.put(ch): inserts one character into stream • stream.close(): closes an opened file stream • stream.eof(): return true if end of stream is reached and false otherwise • stream.fail(): returns true if a precedent open has failed and false otherwise

10. 8.2 External Files • Batch processing • Read data from a file (not from keyboard) •  data can be examined •  don’t need to retype data when you rerun program • Requires use of data files (save to disk) • Batch can be run during off peak use • allows things to be complete at start of day • Helpful is to echo-print (on the screen) read data • Interactive processing • Real time systems • Ok for smaller programs • Programs that complete quickly

11. Files • Naming (system-dependent) • Directory name e.g. /Myfiles/ • File name e.g. Payroll.txt • Extensions: .cc .dat .out .in .txt • How to attach files to the stream • stream object • external file name • internal name • open • Additional functions as part of fstream class

12. Files • Declare the stream to be processed need to #include <fstream> ifstream ins; // input stream ofstream outs; // output stream • Need to open the files ins.open (inFileName); outs.open (outFileName);

13. Files • #define associates the name of the stream with the actual file name  You can directly give file names • fail() function - returns true (nonzero) if file fails to open • Program CopyFile.cpp demonstrates the use of the other fstream functions • get , put, close and eof

14. CopyFile.cpp // File: CopyFile.cpp // Copies file InData.txt to file OutData.txt #include <cstdlib> #include <fstream> using namespace std; // Associate stream objects with external file // names #define inFile "InData.txt" #define outFile "OutData.txt"

15. CopyFile.cpp // Functions used ... // Copies one line of text int copyLine(ifstream&, ofstream&); int main() { // Local data ... int lineCount; ifstream ins; ofstream outs;

16. CopyFile.cpp // Open input and output file, exit on any // error. ins.open(inFile); if (ins.fail ()) { cerr << "*** ERROR: Cannot open " << inFile << " for input." << endl; return EXIT_FAILURE; // failure return } // end if

17. CopyFile.cpp outs.open(outFile); if (outs.fail()) { cerr << "*** ERROR: Cannot open " << outFile << " for output." << endl; return EXIT_FAILURE; // failure return } // end if // Copy each character from inData to outData. lineCount = 0; do {

18. CopyFile.cpp if (copyLine(ins, outs) != 0) lineCount++; } while (!ins.eof()); // Display a message on the screen. cout << "Input file copied to output file." << endl; cout << lineCount << " lines copied." << endl; ins.close(); outs.close(); return 0; // successful return }

19. CopyFile.cpp // Copy one line of text from one file to another // Pre: ins is opened for input and outs for // output. // Post: Next line of ins is written to outs. // The last character processed from // ins is <nwln>; // the last character written to outs // is <nwln>. // Returns: The number of characters copied. int copyLine (ifstream& ins, ofstream& outs) {

20. CopyFile.cpp // Local data ... const char NWLN = '\n'; char nextCh; int charCount = 0; // Copy all data characters from stream ins to // stream outs. ins.get(nextCh); while ((nextCh != NWLN) && !ins.eof()) { outs.put(nextCh); charCount++;

21. CopyFile.cpp ins.get (nextCh); } // end while // If last character read was NWLN write it // to outs. if (!ins.eof()) { outs.put(NWLN); charCount++; } return charCount; } // end copyLine

22. CopyFile.cpp Program Output Input file copied to output file. 37 lines copied.

23. File Processing • Newline character eof() function returns a False if file is not empty while ( ! ins.eof()) { do stuff } • Could have used getline(): string line; linCount = 0; getline(ins, line); while(line.lentgh() != 0) { lineCount++; outs << line << endl; getline(ins, line); }

24. 8.3 Using External File Functions • Payroll Case Study Program 1: computes salary using hours and rate Input file: e.g. Adam Smith 35.5 7.25<nwln> Thomas New 40.0 6.50 <nwln> Ayisha Martin 20.0 8.00 <nwln><eof> Output file: e.g. Adam Smith $257.38<nwln> Thomas New $260.00<nwln> Ayisha Martin $160.00<nwln><eof> Program 2: (not handled here) Does further processing on output file of program 1

25. Payroll Case Structure Chart processEmp

26. ProcessEmp Structure Chart

27. Payroll.cpp // File: Payroll.cpp // Creates a company employee payroll file // computes total company payroll amount #include <fstream> #include <cstdlib> #include "money.h" #include "money.cpp" using namespace std;

28. Payroll.cpp // Associate streams with external file names #define inFile "EmpFile.txt" // employee file #define outFile "Salary.txt" // payroll file // Functions used ... // PROCESS ALL EMPLOYEES AND COMPUTE TOTAL money processEmp(istream&, ostream&); int main() { ifstream eds; ofstream pds; money totalPayroll;

29. Payroll.cpp // Prepare files. eds.open(inFile); if (eds.fail ()) { cerr << "*** ERROR: Cannot open " << inFile << " for input." << endl; return EXIT_FAILURE; // failure return } pds.open(outFile); if (pds.fail()) {

30. Payroll.cpp cerr << "***ERROR: Cannot open " << outFile << " for output." << endl; eds.close(); return EXIT_FAILURE; // failure return } // Process all employees and compute total // payroll. totalPayroll = processEmp(eds, pds); // Display result. cout << "Total payroll is " << totalPayroll << endl;

31. Payroll.cpp // Close files. eds.close(); pds.close(); return 0; }

32. Payroll.cpp // Insert processEmp here. // Process all employees and compute total // payroll amount // Pre: eds and pds are prepared for // input/output. // Post: Employee names and salaries are // written from eds to pds // and the sum of their salaries is returned. // Returns: Total company payroll money processEmp (istream& eds, ostream& pds) {

33. Payroll.cpp string firstName; string lastName; float hours; // input: hoursWorked money rate; // input: hourly rate money salary; // output: gross salary money payroll; // return value - total company payroll payroll = 0.0; // Read first employee's data record. eds >> firstName >> lastName >> hours >> rate;

34. Payroll.cpp while (!eds.eof()) { salary = hours * rate; pds << firstName << “ “ <<lastName << “ “ << salary << endl; payroll += salary; // Read next employee's data record. eds >> firstName >> lastName >> hours >> rate; } // end while return payroll; } // end processEmp

35. PayrollFile.cpp Program Output Total payroll is $677.38

36. 8.4 More on Reading String Data • Getline - could be used to process an entire line of data • Use # as a delimiter character getline (eds, name, ‘#’); • Advance the newline getline (eds, name, ‘\n’); • Use care when choosing cin, get or getline

37. Getline() and Ignore() • getline(istream& in, string& s) Reads a line from input stream in and stores it in s • getline(istream& in, string& s, char delimiter) Reads all characters up to ‘delimiter’ and stores them in s (delimiter is read but not stored in s!) • ins.ignore(int n, char delimiter) Extracts (but not store) up to n characters from input stream ins until the first ‘delimiter’ character is encountered. Delimiter is extracted but not stored

38. 8.5 Input/Output Manipulators • Chapter 5 covered setw width • Also endl has been introduced • boolalpha has been also used to get ‘true’ and ‘false’ from keyboard • Can be used with the cout and << • #include <iomanip> when using manipulators • Can be used with external files like cin and cout

39. I/O Manipulators • setw(int n): set the width of the next output • setprecesion(int n): sets the precision for (float) numbers (default is 6) • boolalpha: enables true/false for I/O • noboolalpha: disable previous operation • fixed: decimal notation of floats • scientific: scientific notation of floats • showpoint: display decimal point also for integers • noshowpoint: undo previous operation • left: left-adjust output in field • right: right-adjust (default) • skipws: skip white spaces on input (default) • noskipws: undo previous operation

40. Formatting with State Flags • Depending on the setiosflags or unsetiosflags • Output can be controlled by other format state flag • Flags are enumerated types • ios::flagname • Flags e.g.: • boolalpha, fixed, left, right, showpoint etc • Examples: cin.setf(ios::boolalpha); cout.setf(ios::boolalpha);

41. 8.6 Common Programming Errors • Connecting streams and external files • Declare stream object and open the file • Watch use of while loops when processing • Test values see what you actually have • Reading past the eof • White space • Newline character • Formatting via flags