Department of Computer and Information Science, School of Science, IUPUI

1. Department of Computer and Information Science,School of Science, IUPUI Input/Output Streams, Part 2 Dale Roberts, Lecturer Computer Science, IUPUI E-mail: droberts@cs.iupui.edu

2. Stream Manipulators • C++ provides various stream manipulators that perform formatting tasks: • setting widths, precision, filling, flushing streams, skipping white spaces, inserting new line, inserting a null character, etc.…..

3. Integral Stream Base • Integers are normally represented as base 10 values. • To change the base in which integers are interpreted on a stream, insert different manipulators – hex, oct – to reset the stream to decimal insert dec. • The base of a stream may also be changed by the stream manipulator setbase, which takes one integer argument of 10, 8 or 16 to set the base. • As setbase takes an argument, it is called a parameterized stream manipulator – requires the inclusion of <iomanip.h> file

4. Floating Point Precision • Controlling of the floating point precision (i.e., number of digits to the right side of the decimal point) is done by setprecision (manipulator) or precision (member function). • A call to these, sets the precision for all subsequent output operations until the next precision-setting call is made. • A call to precision without arguments returns the current precision setting.

5. Field Width • The ios width member function sets the field width (i.e., the number of character positions in which a value should be output or the number of characters that should be input) and returns the previous width. • If values processed are smaller than the field width, fill characters are inserted as padding. • A value wider than the designated width will not be truncated – the full number is printed.

6. Other Manipulators • User-defined • Stream Format State Flags (specifies the kind of formatting to be performed during stream I/O operations) • trailing zeros, justification, padding, stream base, scientific notation, upper/lower cases, setting/resetting format flags, etc.

7. File Streams • Provides high level support for file operations in C++ • Consists of three components: • fstream - allows both input and output • ifstream - allows only input • ofstream - allows only output

8. Files -- fstream class • Inherits from fstreambase and iostream classes • fstreambase inherits from ios class • iostream – inherits from istream and ostream classes • ifstream – inherits from fstreambase and istream classes • ofstream – inherits from fstreambase and ostream classes

9. File Stream Functions • Contains the following functions: • open() - opens the stream • close() - closes the stream • attach() - attaches the stream to file descriptor • setbuf() - set the stream buffer • rdbuf() - returns the pointer to stream buffer • str() - returns a pointer to the buffer array

10. File Streams - Syntax • Syntax fstream(); fstream(const char *sFileName, int nMode, int nProt = 0664); fstream(filedesc fdif);

11. File Processing Modes • nMode can be any of the following: • ios::in - input processing • ios::out - output processing • ios::trunc - discard the file contents • ios::nocreate - the file must exist in order to write • ios::noreplace - cannot rewrite to an existing file • ios::binay - open the file in binary mode • ios::app - append the new data to the contents of the file • ios::ate - open the file for output and move to the end • ios::in|ios::out - both input and output

12. File Protection Modes • nProt can be one of the following: • filbuf::shcompat - compatibility share mode • filebuf::sh_none - no sharing • filebuf::sh_read - read sharing • filebuf::sh_write - write sharing • filebuf::sh_read|filebuf::sh_write - both read and write sharing

13. File Streams - Example • fstream my_file; • fstream myfile(“cs265.txt”, ios::in) • fstream myfile(“cs265.txt”, ios::out) • const int nMAX_SIZE = 256; char buf[nMAX_SIZE]; • filedesc fdesc = my_file.fd(); • fstream fs(fdesc);

14. File Streams - open() • Opens a file as a stream • Syntax void open(const char *sfile, int nMode, int nProt = 0664); • Usage fstream my_file; my_file.open(“cs265.txt”, ios::out);

15. File Streams - close() • Close the opened file. • The stream’s error flag is cleared unless the close fails. • Syntax void close() • Usage my_file.close();

16. File I/O - Example • #include<iostream.h> #include<fstream.h> • main() { // fIn and fOut are objects of class fstream fstream fIn, fOut; int nCnt = 0; //for byte count; char cCh; • //Open the file copy.in for reading fIn.open("copy.in", ios::in); • //Open the file copy.out for writing fOut.open("copy.out", ios::out);

17. File I/O – Example contd… • //Until the end of file is reached, read from //the file and write it to the out file and echo on the screen. while(fIn.get(cCh)) { fOut.put(cCh); cout.put(cCh); //echo on terminal ++nCnt; } • //Write the final byte count cout << "[ " << nCnt << " ]" << endl; fOut << nCnt; • //Close the files fIn.close(); fOut.close(); • return 0;}

18. File I/O - Files • copy.in abcd efg hi j • copy.out abcd efg hi j 14