File Processing - File Operations MVNC1 Fundamental File Processing Operations C++ File Processing.

File Processing - File Operations MVNC 1

Fundamental File Processing Operations

C++

File Processing


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


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


File Access

IntroductionWriting 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


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.


Input/Output Redirection

prog2 < infile.dat > outfile.dat reads from ‘infile.dat’ and outputs to

'outfile.dat'.


File creation/replacement

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


File Appending

If you want to APPEND to the current 'outfile.dat', useprog >> outfile.dat

(>> means append).


C++ header files

Cstdio.h - types and operations used for C streams

C++ iostream.h - stream operationsfstream.h - file stream operations


C++ Stream classes

C++ streams are implemented as classesostream - output streamistream - input stream

cin, cout, and cerr are three predefined instances of streamscin - is an instance of istreamcout and cerr are instances of ostream

These streams are defined in iostream.h File manipulation methods are defined in

fstream.h


C++ Stream constructors

fstream ();leave the stream unopened

fstream (char * filename, int mode);open the file filename using mode modeMode 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:app - (for output) append to the end of file– ios:binary - opens in binary mode (text is default)


C++ Stream destructors

~fstream();destroys the fstream object. File is closed of

openned by the constructor or the open member function.


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


C++ Formatted Stream I/O operators

<<output to fstreamdefined for all built in data types

>>input from fstreamAlso defined for all built in data types

It is important to understand that these operators format based on the passes datatype

Many modi


fstream subclasses

ifstreamfor inputios:in implied

ofstreamfor outputios:out implied

All the fstream methods are inherited.


Example: C++ File listing program

#include <fstream.h>void main (){ char ch;

fstream file; // declare fstream unattachedchar filename[20];cout <<"Enter the name of the file: "

<<flush; // force outputcin >> 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();}


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);


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).


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.


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::begios:::curios::end


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


String Handling

string.h definitions char *strcat (char *dest,

const char *src); concatenate src to end of dest.


String Handling

char *strncat(char *dest, const char *src, size_t maxlen);

concatenate maxlen chars of src onto dest.


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, int c); return pointer to last c in s, NULL if not

present.


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.


String Handling

int strncmp(const char *s1, const char *s2, size_t maxlen);

same as strcmp, but only uses n chars.


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.


String Handling

size_t strlen (const char *s); returns length of s;


Strings examplemain(){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); strcpy(mixed,name1); strcat(mixed," "); strcat(mixed,name2); printf("Both names are %s\n",mixed);}

File Processing - File Operations MVNC1 Fundamental File Processing Operations C++ File Processing.

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