Developed By : Ms. K. M. Sanghavi

Transcription

1 Developed By : Ms. K. M. Sanghavi

2 Designing Our Own Manipulators We can design our own manipulators for certain special purpose.the general form for creating a manipulator without any arguments is: ostream & manipulator(ostream & output) { (code) return output } Here the manipulator is the name of the manipulator under creation.

3 The following function defines a manipulator called unit that dispalys inches : ostream & unit(ostream &output) { output<< inches ; return output; } The statement cout<<36<<unit; will produce the following output 36 inches

4 We can also create manipulators that could represent a sequence of operations. Example: ostream & show(ostream & output) { output.setf(ios::showpoint); output.setf(ios::showpos); output<<setw(10); return output; }

5 Program illustrates the creation and use of the user-defined manipulators. The program creates two manipulators called currency and form which are used in the main program.

6 #include<iostream.h> #include<iomanip.h> ostream & currency(ostream & output) { output<< Rs ; return output; }

7 ostream& form(ostream & output) { output.setf(ios::showpos); output.setf(ios::showpoint); output.fill( * ); output.precision(2); output<<setiosflags(ios::fixed)<<setw(10); return output; } int main() { cout<<currency <<form<<7864.5; return 0; }

8 The output of Program would be: Rs**

9 Stream Errors bool ios::good() : returns true if no error bool ios::bad() : returns true if invalid read/write bool ios::eof() : returns true if end of file reach bool ios::fail() : returns true if input operation fails void ios::clear() : clears all the flags

10 int main() { int num; bool valid = false; while (!valid) { valid = true; //Assume the cin will be an integer. } cout << "Enter an integer value: " << endl; cin >> num; if(cin.fail()) //cin.fail() checks to see if the value in the cin //stream is the correct type, if not it returns true, //false otherwise. { cin.clear(); //This corrects the stream. cin.ignore(); //This skips the left over stream data. cout << "Please enter an Integer only." << endl; valid = false; //The cin was not an integer so try again. }

11 cout << "You entered: " << num << endl; } system("pause"); return 0;

12 File I/O Streams Stream ifstream ofstream fstream Description Reads from files Writes on files Read & Write From/To files To perform File I/o We include <fstream.h> in the program

13 ifstream Input file stream Class open() is a member function of the class ifstream Inherited functions of ifstream class, from the class istream are get() getline() read() seekg() tellg()

14 ofstream Output file stream Class open() is a member function of the class ofstream Inherited functions of ofstream class, from the class ostream are put() write() seekp() tellp()

15 File Handling Classes

16 Opening a File Use method open() File Handling Classes Or immediately in the constructor (the natural and preferred way). copyrights Elhanan Borenstein

17 Opening a File Before data can be written to or read from a file, the file must be opened. ifstream inputfile; inputfile.open( customer.dat ); Another Syntax void open(const char* filename, int mode); filename file to open (full path or local) mode how to open (one or more of the following using ) 17

18 Modes can be File Handling Classes ios::app append ios::ate open with marker at the end of the file ios::in / ios::out (the defaults of ifstream and ofstream) ios:nocreate / ios::noreplace open only if the file exists / doesn t exist ios::trunc open an empty file ios::binary open a binary file (default is textual) Don t forget to close the file using the method close()

19 Opening a File at Declaration fstream f; f.open( names.dat, ios::in ios::out ios:app); 19

20 Testing for Open Errors datafile.open( cust.dat, ios::in); if (!datafile) { cout << Error opening file.\n ; } 20

21 Querying a File is_open() Checking whether the file was open correctly. (for compatibility with C, the operator! was overloaded). rd_state() returns a variable with one or more (check with AND) of the following options: ios::goodbit OK ios::eofbit marker on EOF File Handling Classes ios::failbit illegal action, but alright to continue ios:badbit corrupted file, cannot be used. We can also access the bit we wish to check with eof(), good(), fail(), bad(). clear() is used to clear the status bits (after they were checked). copyrights Elhanan Borenstein

22 Another way to Test for Open Errors f.open( cust.dat, ios::in); if (f.fail()) { cout << Error opening file.\n ; } 22

23 Detecting the End of a File The eof() member function reports when the end of a file has been encountered. if (f.eof()) f.close(); 23

24 Moving within the File seekg() / seekp() moving the reading (get) / writing (put) marker two parameters: offset and anchor File Handling Pointers tellg() / tellp() getting the position of the reading (get) / writing (put) marker copyrights Elhanan Borenstein

25 Reading /Writing from/to Textual Files To write: put() writing single character << operator writing an object To read: get() reading a single character of a buffer getline() reading a single line >> operator reading a object File Handling Classes #include <fstream.h> main() { // Writing to file ofstream OutFile("my_file.txt"); OutFile<<"Hello "<<5<<endl; OutFile.close(); int number; char dummy[15]; // Reading from file ifstream InFile("my_file.txt"); InFile>>dummy>>number; } InFile.seekg(0); InFile.getline(dummy, sizeof(dummy)); InFile.close();