1. Fundamental File Processing Operations C++

2. C++ Standard Input and Output
The stream model of text input/output.
A text stream consists of a sequence of lines;
A line consists of zero or more characters terminated with a newline ('\n') character.
Even if the computer system does not conform to that model, the library must hide the deviations

3. C++ Standard Input and Output
C++ has three pre-opened streams as well:
cin
standard input
connected to keyboard
cout
standard output
connected to screen
cerr
standard output for error messages
to screen

4. File Access Introduction
Writing cout (stdout) and reading from cin (stdin is) very similar to file I/O;
C++ (C) treats cin (stdin) and cout (stdout) as files.
The major difference is that cxxx (stdxxx) are already connected to the program (and opened) by the system

5. Input/Output Redirection
On MS-DOS and UNIX systems,
prog > outfile.dat
redirects all cin (stdout) output to 'outfile.dat'.
Likewise, input redirection
prog1 < infile.dat
reads from 'infile.dat', for every cin (stdin) input.

6. Input/Output Redirection
prog2 < infile.dat > outfile.dat
reads from ‘infile.dat’ and outputs to 'outfile.dat'.

7. File creation/replacement
In the previous examples:
if 'outfile.dat' exists, it is deleted and replaced,
if it does not exist, it is created.

8. File Appending If you want to APPEND to the current 'outfile.dat', use
prog >> outfile.dat
(>> means append).

9. C++ header files C
stdio.h - types and operations used for C streams
C++
iostream.h - stream operations
fstream.h - file stream operations

10. C++ Stream classes C++ streams are implemented as classes
ostream - output stream
istream - input stream
cin, cout, and cerr are three predefined instances of streams
cin - is an instance of istream
cout and cerr are instances of ostream
These streams are defined in iostream.h
File manipulation methods are defined in fstream.h

11. C++ Stream constructors
fstream ();
leave the stream unopened
fstream (char * filename, int mode);
open the file filename using mode mode
Mode integer defined as ios enumerators:
ios::in - open for input
ios:out - open for output
ios:trunc - (for output) discard contents
ios:app - (for output) append to the end of file
ios:nocreate - causes open to fail if file does not exist
ios:binary - opens in binary mode (text is default)

12. C++ Stream destructors
~fstream();
destroys the fstream object. File is closed of openned by the constructor or the open member function.

13. C++ Stream Methods int open(char * filename, int mode);
int read(unsigned char * dest_addr, int size);
int write(unsigned char * source addr, int size)
Read and write allow for unformatted (raw) I/O

14. C++ Formatted Stream I/O operators
<<
output to fstream
defined for all built in data types
>>
input from fstream
Also defined for all built in data types
It is important to understand that these operators format based on the passes datatype
Many modi

15. fstream subclasses ifstream ofstream
for input
ios:in implied
ofstream
for output
ios:out implied
All the fstream methods are inherited.

16. Example: C++ File listing program
#include <fstream.h>
void main ()
{ char ch;
fstream file; // declare fstream unattached
char filename[20];
cout <<"Enter the name of the file: "
<<flush; // force output
cin >> filename;
file.open(filename, ios::in);
file.unsetf(ios::skipws); // include white space in read
while (1)
{ file >> ch;
if (file.fail()) break;
cout << ch; }
file.close(); }

17. fstream Format manipulators
Stream I/O can be modified with the format manipulators setf and unsetf.
These functions set and clear bits in the format flags.
ios::setf(long iFlags);
ios::unsetf(lond iFlags);
Flags may be “or”ed together with the “|” operator
Example:
myfile.setf(ios::hex | ios::left);

18. fstream Format Flags ios::skipws - Skip white space on input.
ios::left - Left align values; pad on the right with the fill character.
ios::right - Right align values; pad on the left with the fill character (default alignment).
ios::internal - Add fill characters after any leading sign or base indication, but before the value.
ios::dec - Format numeric values as base 10 (decimal) (default radix).
ios::oct - Format numeric values as base 8 (octal).
ios::hex - Format numeric values as base 16 (hexadecimal).

19. fstream Format Flags
ios::showbase - Display numeric constants in a format that can be read by the C++ compiler.
ios::showpoint - Show decimal point and trailing zeros for floating-point values.
ios::uppercase - Display uppercase A through F for hexadecimal values and E for scientific values.
ios::showpos - Show plus signs (+) for positive values.
ios::scientific - Display floating-point numbers in scientific format.
ios::fixed - Display floating-point numbers in fixed format.
ios::unitbuf - Cause ostream::osfx to flush the stream after each insertion. By default, cerr is unit buffered.
ios::stdio - Cause ostream::osfx to flush stdout and stderr after each insertion.

20. Seeking with C++ stream classes
Two forms:
file.seekg(long position);
file.seekg(long offset, origin);
position - position in file
offset - byte offset from origin
origin
ios::beg
ios:::cur
ios::end

21. C Command Line Parameters
Two values passed to main:
int argc - Number of command line arguments (including command)
char *argv[] - Array of pointers to parameter strings.
argc >=1
*argv[0] is always a string containing the file name
*argv[1] is the first argument, and so on

22. String Handling string.h definitions
char *strcat (char *dest, const char *src);
concatenate src to end of dest.

23. String Handling
char *strncat(char *dest, const char *src, size_t maxlen);
concatenate maxlen chars of src onto dest.

24. String Handling char * strchr(const char *s, int c);
return pointer to first c in s, NULL if not present.
char *strrchr(const char *s,
return pointer to last c in s, NULL if not present.

25. String Handling int strcmp(const char *s1, const char *s2);
return negative if s1 lexically less than s2
return 0 if s1==s2;
return positive if s1>s2.

26. String Handling int strncmp(const char *s1,
const char *s2, size_t maxlen);
same as strcmp, but only uses n chars.

27. String Handling char *strcpy (char *dest, const char *src);
copy src to dest.
char *strncpy(char *dest, const char *src, size_t maxlen);
same as strcpy, only n chars.

28. String Handling
size_t strlen (const char *s);
returns length of s;

29. Strings example main() { char name1[12],name2[12],mixed[25];
char title[20];
strcpy(name1,"Rosalinda");
strcpy(name2,"Zeke");
strcpy(title,"This is the title.");
printf(" %s\n\n",title);
printf("Name 1 is %s\n",name1);
printf("Name 2 is %s\n",name2);
if(strcmp(name1,name2)>0) /* returns 1 if name1 > name2 */
strcpy(mixed,name1);
else
strcpy(mixed,name2);
printf("The biggest name alpabetically is %s\n",mixed);
strcat(mixed," ");
strcat(mixed,name2);
printf("Both names are %s\n",mixed); }