Object Oriented Programming using C++: Ch12 Streams and Files.pptx

Object Oriented Programming using C++: Ch12 Streams and Files.pptx

1. Object Oriented Programming Streams and Files Engr . Rashid Farid Chishti [email protected] https://youtube.com/rfchishti https://sites.google.com/site/chishti 1 International Islamic University H-10, Islamabad, Pakistan http://www.iiu.edu.pk Video Lecture

2. Stream Classes A stream is a general name given to a flow of data. In C++ a stream is represented by an object of a particular class. So far we’ve used the cin and cout stream objects. Different streams are used to represent different kinds of data flow. For example, the ifstream class represents data flow from input disk files . Advantages of Streams One reason is simplicity. Another reason is that you can overload existing operators and functions, such as the insertion ( << ) and extraction ( >> ) operators, to work with classes that you create. You should know about C++ streams because they are the best way to write data to files and to format data in memory for later use in text input/output windows and other GUI elements. [ 2 ]

3. The Stream Class Hierarchy [ 3 ]

4. The Stream Class Hierarchy [ 4 ]

5. The Stream Class Hierarchy ios class is the base class for the hierarchy. It contains many constants and member functions common to input and output operations, such as the showpoint and fixed formatting flags The ios class also contains a pointer to the streambuf class, which contains the actual memory buffer into which data is read or written. The istream and ostream classes are derived from ios and are dedicated to input and output, respectively. The istream class contains such functions as get() , getline () , read() , and the overloaded extraction ( >> ) operators, while ostream contains put() and write() , and the overloaded insertion ( << ) operators. The iostream class is derived from both istream and ostream by multiple inheritance. Classes derived from it can be used with devices, such as disk files, that may be opened for both input and output at the same time. [ 5 ]

6. The Stream Class Hierarchy Three classes istream_withassign , ostream_withassign , and iostream_withassign are inherited from istream , ostream , and iostream , respectively. They add assignment operators to these classes. The cout object, is a predefined object of the ostream_withassign class Similarly, the cin is an object of the istream_withassign class The classes used for input and output to the video display and keyboard are declared in the header file IOSTREAM . The classes used specifically for disk file I/O are declared in the file FSTREAM . [ 6 ]

7. Disk File I/O with Streams Most programs need to save data to disk files and read it back in. Working with disk files requires another set of classes: ifstream for input fstream for both input and output and ofstream for output . Objects of these classes can be associated with disk files, and we can use their member functions to read and write to the files . These three classes are declared in the FSTREAM file. [ 7 ]

8. Formatted File I/O In formatted I/O, numbers are stored on disk as a series of characters. Thus 6.02, rather than being stored as a 4-byte type float or an 8-byte type double, is stored as the characters ‘6 ’, ‘.’, ‘0’, and ‘2 ’. This can be inefficient for numbers with many digits, but it’s appropriate in many situations and easy to implement . [ 8 ]

9. // writes formatted output to a file // using << operator #include < fstream > // for file I/O #include < iostream > #include <string> #include < stdlib.h > using namespace std ; int main() { char ch = 'x' ; int j = 77; double d = 6.02; // strings without embedded spaces string str1 = "Rashid" ; string str2 = " Farid " ; // create ofstream object ofstream outfile ( "data.txt" ); 9 Example 1: Writing Data to a File outfile << ch // insert (write) data << j << ' ' // needs space between numbers << d << str1 << ' ' //needs spaces between strings << str2; cout << "File written\n" ; system( "pause" ); return 0; } 1 2 [ 9 ]

10. Example 1: Writing Data to a File If the file doesn’t exist, it is created. If it does exist, it is truncated and the new data replaces the old. The outfile object acts much as cout did in previous programs, so we can use the insertion operator ( << ) to output variables of any basic type to the file. This works because the insertion operator is appropriately overloaded in ostream , from which ofstream is derived. When the program terminates, the outfile object goes out of scope. This calls its destructor, which closes the file, so we don’t need to close the file explicitly There are several potential formatting glitches. First, you must separate numbers (such as 77 and 6.02) with nonnumeric characters . As numbers are stored as a sequence of characters, this is the only way the extraction operator will know, when the data is read back from the file, where one number stops and the next one begins . [ 10 ]

11. Example 1: Writing Data to a File Second, strings must be separated with whitespace for the same reason. This implies that strings cannot contain imbedded blanks . In this example we use the space character (‘ ‘) for both kinds of delimiters . Characters need no delimiters, since they have a fixed length. You can verify that program has indeed written the data by examining the DATA.TXT file with the Windows NOTEPAD accessory or the DOS command TYPE. [ 11 ]

12. // reads formatted output from a file // using >> operator #include < fstream > // for file I/O #include < iostream > #include <string> #include < stdlib.h > using namespace std ; int main() { char ch ; int j; double d; string str1, str2 ; // create ifstream object ifstream infile ( "data.txt " ); //extract (read) data from it infile >> ch >> j >> d >> str1 >> str2 ; 12 Example 2: Reading Data from a File cout << ch << endl // display the data << j << endl << d << endl << str1 << endl << str2 << endl ; system( "pause" ); return 0; } 1 2 [ 12 ]

13. If you’ve ever used MS-DOS, you are probably familiar with command-line arguments, used when invoking a program. They are typically used to pass the name of a data file to an application. For example, you can invoke a word processor application and the document it will work on at the same time: C> wordproc afile.doc Here afile.doc is a command-line argument. How can we get a C++ program to read the command-line arguments? Here’s an example 13 Example 3: Command-Line Arguments #include < iostream > using namespace std ; int main( int argc , char * argv [] ) { // number of arguments cout << " argc = " << argc << endl ; // display arguments for ( int j=0; j< argc ; j ++ ) cout << "Argument " << j << " = " << argv [j] << endl ; return 0; } [ 13 ]

14. Command-Line Arguments And here’s a sample interaction with the program: To read command-line arguments, the main() function (don’t forget it’s a function!) must itself be given two arguments. The first, argc (for argument count), represents the total number of command-line arguments. The first command-line argument is always the pathname of the current program . The remaining command-line arguments are those typed by the user; they are delimited by the space character. In the preceding example they are uno , dos, and tres . [ 14 ]

15. #include < fstream > // for file #include < iostream > #include < process.h > //for exit() using namespace std ; int main( int argc , char * argv [] ) { if ( argc != 2 ) { cerr << "Format: oop filename" << endl ; exit (-1); } char ch ; //character to read ifstream infile ; // to read a file infile.open ( argv [1] ); // open file 15 Example 4: Command-Line Arguments if ( ! infile ) { // check for errors cerr << "\ nCan't open " << argv [1]; exit(-1); } while ( infile.get ( ch ) != 0 ) //read a character cout << ch ; //display the character return 0; } 1 2 [ 15 ]

16. Strings with Embedded Blanks The technique of our last examples won’t work with char* strings containing embedded blanks. To handle such strings, you need to write a specific delimiter character after each string , and use the getline () function, rather than the extraction operator, to read them in. Our next program, outputs some strings with blanks embedded in them . [ 16 ]

17. // file output with strings #include < fstream > // for file I/O #include < iostream > #include < stdlib.h > using namespace std ; int main() { // create file for output ofstream outfile ( "data.txt" ); //send text to file outfile << "I fear thee, ancient!\ n" ; outfile << "I fear thy skinny hand\n" ; outfile << "And thou art long brown ,\n" ; system( "pause" ); return 0; } 17 Example 5 , 6 : Writing and Reading String in a File // file input with strings #include < fstream > // for file I/O #include < iostream > #include < stdlib.h > using namespace std ; int main() { const int MAX = 80; // size of buffer char buffer[MAX]; // character buffer // create file for input ifstream infile ( "data.txt" ); while (! infile.eof ()){ // until end-of-file // read a line of text infile.getline (buffer , MAX); // display it cout << buffer << endl ; } system( "pause" ); return 0; } 1 2 [ 17 ]

18. Writing and Reading String in a File This program requires all the text lines to terminate with the ‘\n’ character, and if you encounter a file in which this is not the case, the program will hang. The program continues to read one string at a time until it encounters an end-of-file ( EOF ) condition. The EOF is a signal sent to the program from the operating system when there is no more data to read. However , checking specifically for an eofbit means that we won’t detect the other error flags, such as the failbit and badbit , which may also occur, although more rarely. To do this, we can change our loop condition: while ( infile.good ()){ // until any error encountered You can also test the stream directly. If everything is going well, the object infile returns a nonzero value which is a pointer. Thus we can rewrite our while loop again: while ( infile ){ // until any error encountered [ 18 ]

19. // file output with characters #include < fstream > // for file I/O #include < iostream > #include < stdlib.h > using namespace std ; int main() { string str = "Time is a great teacher ," " but unfortunately it kills all its" " pupils. Berlioz " ; // create file for output ofstream outfile ( "data.txt" ); for ( unsigned int j = 0; j < str.size (); j++ ) // write it to file outfile.put ( str [ j ] ); cout << "File written\n" ; system( "pause" ); return 0; } 19 Example 7 , 8 : Character I/O // file input with characters #include < fstream > // for file I/O #include < iostream > #include < stdlib.h > using namespace std ; int main() { char ch ; // character to read // create file for output ifstream infile ( "data.txt" ); // read until the EOF is reached // or an error occurs while ( infile ){ infile.get ( ch ); // read a character cout << ch ; // display it } cout << endl ; system ( "pause" ); return 0; } 1 2 [ 19 ]

20. Binary I/O You can write a few numbers to disk using formatted I/O, but if you’re storing a large amount of numerical data it’s more efficient to use binary I/O, in which numbers are stored as they are in the computer’s RAM memory, rather than as strings of characters. In binary I/O an int is stored in 4 bytes, whereas its text version might be “12345”, requiring 5 bytes. Similarly, a float is always stored in 4 bytes, while its formatted version might be “6.02314e13”, requiring 10 bytes . example shows how an array of integers is written to disk and then read back into memory , using binary format. We use write () , a member of ofstream ; and read () , a member of ifstream . These functions think about data in terms of bytes (type char ). They don’t care how the data is formatted, they simply transfer a buffer full of bytes from and to a disk file. [ 20 ]

21. // binary input and output with integers #include < fstream > //for file streams #include < iostream > #include < stdlib.h > using namespace std ; const int MAX = 100; //size of buffer int buff[MAX]; //buffer for integers int main () { int i ; for ( i = 0; i < MAX; i ++) // fill buffer with data { 0, 1, 2, ... ,99} buff[ i ] = i ; ofstream os ( "numbers.txt" , ios ::binary ); // create output stream os.write (( char *)buff, MAX * sizeof ( int )); // write to it os.close (); // must close it for ( i =0; i < MAX; i ++) // erase buffer buff[ i ] = 0; ifstream is( "numbers.txt" , ios ::binary ); // create input stream is.read (( char *)buff, MAX * sizeof ( int )); // read from it Example 9: Binary I/O with integers (1/2) [ 21 ]

22. for ( i = 0; i < MAX; i ++) // check data if (buff[ i ] != i ){ cerr << i << " Data is incorrect\n" ; return 1; } cout << "Data is correct\n" ; system( "pause" ); return 0; } Example 9: Binary I/O with integers (2/2 ) [ 22 ]

23. Object I/O Since C++ is an object-oriented language, it’s reasonable to wonder how objects can be written to and read from disk. The next examples show the process When writing an object, we generally want to use binary mode. This writes the same bit configuration to disk that was stored in memory, and ensures that numerical data contained in objects is handled properly. Here’s the listing for OPERS, which asks the user for information about an object of class person, and then writes this object to the disk file PERSON.DAT [ 23 ]

24. #include < fstream > // for file streams #include < iostream > using namespace std ; class person { // class of persons protected : char name[80]; // person’s name short age; // person’s age public : void getData () { //get person’s data cout << "Enter name : " ; cin.get (name,80); cout << "Enter age : " ; cin >> age; } }; int main() { person pr1; // create a person pr1.getData(); // get data for person 1 ofstream outfile ( "PERSON.DAT" , ios ::binary); // create ofstream object outfile.write (( char *) &pr1, sizeof (pr1)); // write to it return 0; } Example 10: Writing Object to a File [ 24 ]

25. // saves person object to disk #include < fstream > // for file streams #include < iostream > using namespace std ; class person { protected : char name[80]; // person’s name short age; // person’s age public : void showData () { // display person’s data cout << "Name: " << name << endl ; cout << " Age : " << age << endl ; } }; int main() { person pr1; // create a person ifstream infile ( "PERSON.DAT" , ios ::binary); infile.read (( char *) &pr1, sizeof (pr1 )); // read from file pr1.showData(); return 0; } Example 10: Reading Object from a File [ 25 ]

26. i stream Functions [ 26 ] Function Purpose >> Formatted extraction for all basic (and overloaded) types. get( ch ) Extract one character into ch . getline ( str , MAX ) Extract one line into array str , until MAX characters or the ‘\n’ character getline ( str , MAX , DELIM ) Extract characters into array str , until MAX characters or the DELIM character. putback ( ch ) Insert last character read back into input stream. ignore( MAX , ‘\n’ ) Extract and discard up to MAX characters until (and including) the specified delimiter ‘\n’ . ch = stream.peek ( ) Read one character, leave it in stream. read( str , MAX ) For files , extract up to MAX characters into str , until EOF. seekg ( n ) Set distance ( n bytes) of file pointer from start of file. e.g. infile.seekg (0, ios ::end); // go to 0 bytes from end seekg ( pos , seek_dir ) Set distance (in bytes) of file pointer from specified place in file. seek_dir can be ios ::beg, ios ::cur, ios ::end. tellg ( ) Return position (in bytes) of file pointer from start of file. e.g. int endposition = infile.tellg ();

27. ostream Functions [ 27 ] Function Purpose << Formatted insertion for all basic (and overloaded) types. put( ch ) Insert one character ch into stream. flush() Flush buffer contents and Insert newline. write( str , SIZE ) Insert SIZE characters from array str into file. seekp ( n ) Set distance in n bytes of file pointer from start of file. seekp ( pos , seek_dir ) Set distance (in bytes) of file pointer from specified place in file. seek_dir can be ios ::beg, ios ::cur, ios ::end. tellgp ( ) Return position (in bytes) of file pointer from start of file. e.g. int endposition = outfile.tellg ();

28. #include < fstream > // for file streams #include < iostream > using namespace std ; class Book { protected : char title[80]; char auther [80 ]; double price ; public : void Add_Record (); void Read_All (); void Search(); void Delete(); }; Example 11: Books Management System (1/8) [ 28 ]

29. void Book :: Add_Record () { cout << "Enter title : " ; // eat chars, including newline cin.ignore (80 , '\n' ); cin.getline (title , 80); cout << "Enter Auther : " ; cin.getline ( auther , 80); cout << "Enter Price : " ; cin >> price; cout << "Title = " << title << endl ; cout << " Auther = " << auther << endl ; cout << "Price = " << price << endl ; ofstream outfile ; outfile.open ( "books.txt" , std :: ios_base ::app); outfile << title << "\\" << auther << "\\" << price << endl ; system( "pause" ); } Example 11: Books Management System (2/8) [ 29 ]

30. void Book :: Read_All () { system( "CLS" ); const int MAX = 240; int S_No = 0; char buffer[MAX]; // character buffer ifstream infile ( "books.txt" ); while ( infile ) { infile.getline (buffer, MAX); if ( strlen (buffer) > 0) { const char * delim = "\\" ; char * next_token ; char * title = strtok_s (buffer, delim , & next_token ); char * auther = strtok_s ( NULL , delim , & next_token ); char * prc = strtok_s ( NULL , delim , & next_token ); cout << "#" << ++ S_No << endl ; cout << " Title = " << title << endl ; cout << " Auther = " << auther << endl ; cout << " Price = " << prc << endl ; } } } Example 11: Books Management System (3/8) [ 30 ]

31. void Book ::Search() { int S_No = 0; cout << "Enter title to Search: " ; // eat chars, including newline cin.ignore (80 , '\n' ); cin.getline ( this - >title, 80); system( "CLS" ); const int MAX = 240; // size of buffer char buffer[MAX]; // character buffer ifstream infile ( "books.txt " ); while ( infile ) { infile.getline (buffer, MAX ); if ( strlen (buffer) > 0) { const char * delim = "\\" ; char * next_token ; char * title = strtok_s (buffer, delim , & next_token ); char * auther = strtok_s ( NULL , delim , & next_token ); char * prc = strtok_s ( NULL , delim , & next_token ); char * output = strstr (title, this ->title ); Example 11: Books Management System (4/8) [ 31 ]

32. S_No ++; if (output) { cout << "#" << S_No << endl ; cout << "Title = " << title << endl ; cout << " Auther = " << auther << endl ; cout << "Price = " << prc << endl ; cout << "_________________________________" << endl ; } } } } void Book ::Delete() { system( "CLS" ); const int MAX = 240; // size of buffer int R_No = 0, S_No = 0; cout << "Please Enter Record Number: " ; cin >> R_No ; char buffer[MAX]; // character buffer ifstream infile ( "books.txt" ); ofstream outfile ( "temp.txt" ); Example 11: Books Management System (5/8) [ 32 ]

33. while ( infile ) { infile.getline (buffer, MAX); if ( strlen (buffer) > 0) { const char * delim = "\\" ; char * next_token ; char * title = strtok_s (buffer, delim , & next_token ); char * auther = strtok_s ( NULL , delim , & next_token ); char * prc = strtok_s ( NULL , delim , & next_token ); S_No ++; if ( S_No == R_No ) { char choice; cout << "#" << S_No << endl ; cout << " Title = " << title << endl ; cout << " Auther = " << auther << endl ; cout << " Price = " << prc << endl ; cout << "Do you want to Delete this Record [y/n]?: " ; cin >> choice; if (choice == 'y' ) continue ; Example 11: Books Management System (6/8) [ 33 ]

34. else outfile << title << "\\" << auther << "\\" << prc << endl ; } else outfile << title << "\\" << auther << "\\" << prc << endl ; } } infile.close (); outfile.close (); remove( "books.txt" ); rename( "temp.txt" , "books.txt" ); } int main() { Book b; while (1) { char choice; cout << "[Operations]" << endl ; cout << "A - Add" << endl ; cout << "D - Delete" << endl ; Example 11: Books Management System (7/8) [ 34 ]

35. cout << "R - Read All" << endl ; cout << "S - Search Title" << endl ; cout << "Q - Quit " << endl ; cin >> choice; switch (choice) { case 'A' : case 'a' : b.Add_Record (); break ; case 'D' : case 'd' : b.Delete (); break ; case 'R' : case 'r' : b.Read_All (); break ; case 'S' : case 's' : b.Search (); break ; case 'Q' : case 'q' : exit(0); default : cout << "Wrong Choice" << endl ; } } return 0; } Example 11: Books Management System (8/8) [ 35 ]