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Class 15 Honors. Objectives. Understand some common file I/O functions Set up a program for writing to a file Read information from a file. 3 Steps to Use a File. The file must be opened. If the file does not exist, opening it means creating it.

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objectives
Objectives
  • Understand some common file I/O functions
  • Set up a program for writing to a file
  • Read information from a file
3 steps to use a file
3 Steps to Use a File
  • The file must be opened. If the file does not exist, opening it means creating it.
  • Information is then saved to the file, read from the file, or both.
  • When the program is finished using the file, the file must be closed.

P. 701

file name and

P. 706

Table 12-4

File Name and

Extension File Contents

MYPROG.BAS BASIC Program

MENU.BAT DOS Batch File

INSTALL.DOC Documentation File

CRUNCH.EXE Executable File

GAMES.GRP Windows Group File

BOB.HTML HTML

3DMODEL. JAVA java prog. or applet

INVENT.OBJ Object File

PROG1.PRJ Borland C++ Porj. File

ANSI.SYS Sys. Device Driver

README.TXT Text File

CLIENTS.DAT

writing information to a file
Writing Information to a File

File:

In Memory

Variables:

25

40

10

10

X

Y

25

Z

40

Data is copied from variables

into the file

reading information from a file
Reading Information from a File

File:

In Memory

Variables:

25

40

10

10

X

Y

25

Z

40

Data is copied from the file

into variables

file stream

P. 700Table 12-1

File Stream

Data Type

ofstream

Description

Output File Stream. This data type can be used to create files and write information to them. With the ofstream data type, information may only be copied from variables to the file, but not vice-versa.

file stream1

P. 700Table 12-1

File Stream

Data Type

ifstream

Description

Input File Stream. This data type can be used to read information from files into memory. With the ifstream data type, information may only be copied from the file into variables, not but vice-versa.

file stream2
File Stream

P. 700Table 12-1

Data Type

fstream

Description

File Stream. This data type can be used to create files, write information to them, and read information from them. With the fstream data type, information may be copied from variables into a file, or from a file into variables.

slide10
ofstream outClientFile(“clients.dat”, ios::out);

if (!outClientFile) {

cerr<<“File could not be opened”

<< endl;

exit (1); // prototype in stdlib

}

slide11

ofstream outclientFile(“clients.dat”, ios::out);ofstream outclientFile;outclientFile.open(“clients.dat”, ios::out);

slide12

Opening Modes for Files

  • ios::app- Write all output to the end of the file
  • ios::ate- Move to the end of the original file when file is opened. Enable data to be written anywhere in the file

Table 12- 2p. 701

slide13

Opening Modes for Files (Cont’d)

  • ios::in- Open a file for input.
  • ios::out- Open a file for output.
  • ios::trunc- Discard the file’s contents if it exists (this is also the default action for ios::out)

Table 12- 2p. 701

slide14

Opening Modes for Files (Cont’d)

  • ios::nocreate- If the file does not exist, the open operation fails.
  • ios::noreplace- If the file exists, the open operation fails.
  • ios::binary- Information read or written in pure binary format
slide15

#include <fstream>

using namespace std;

int main()

{ fstream DataFile;

char FileName[81];

cout << “Enter the name of the file you wish to open\n”;

cout << “or create:”;

cin.getline(FileName);

DataFile.open(FileName, ios::out);

cout << “The file ” << FileName <<

”was opened.\n”;

}

P. 702Pgrm. 12-1

slide16

#include <fstream> using namespace std;

int main()

{ fstream DataFile;

char FileName[81];

cout << “Enter the name of the file you wish to open\n”;

cout << “or create:”;

cin.getline(FileName);

DataFile.open(FileName, ios::out);

cout << “The file ” << FileName <<

”was opened.\n”;

}

slide17

#include <fstream.h>

void main(void)

{ fstream DataFile;

DataFile.open(“demofile.txt”, ios::out);

if (DataFile == 0)

{ cout << “File open error!” ,, endl;

return; }

cout << “File opened successfully.\n”;

cout << “Now writing information to the file.\n”;

DataFile << “Jones\n”;

DataFile << “Smith\n”;

DataFile <<“Willis\n”;

DataFile << “Davis\n”;

DataFile.close( ); }

P. 702Pgrm. 12-1

program screen output
Program Screen Output

P. 702

File opened successfully

Now writing information to the file.

Done.

Output to File DEMOFILE.TXT

Jones

Smith

Wilis

Davis

slide19

S

m

i

t

\n

n

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h

i

l

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s

\n

W

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v

s

a

\n

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<EOF>

P. 702

slide20

#include <fstream>

int main()

{ fstream DataFile;

DataFile.open(“demofile.txt”, ios::out);

DataFile << “Jones\n”;

DataFile << “Smith\n”;

DataFile.close( );

DataFile.open(“demofile.txt”, ios::app);

DataFile << “Willis\n”;

DataFile << “Davis\n”;

DataFile.close( );

}

P. 703Pgrm. 12-2

slide21

Output to File DEMOFILE.TXT

Jones

Smith

Wilis

Davis

Pg. 703

slide22

S

m

i

t

\n

n

e

h

i

l

o

J

s

\n

W

i

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D

l

\n

v

s

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\n

i

<EOF>

P. 704Fig. 12- 3

this program writes three rows of numbers to a file
//This program writes three rows of//numbers to a file.

P. 709Pgrm. 12-4

#include <fstream>

# include <iomanip>#include <iostream>using namespace std;

int main ()

{ fstream OutFile(“table.txt, ios::out);

int Nums[3] [3] = { 2897, 5, 837,

34, 7, 1623,

390, 3456, 12 };

write three rows of numbers
//Write three rows of numbers

for (int Row = 0; row < 3; Row++)

{

for (int Col = 0; Col < 3; Col++)

{

OutFile << setw(4)<< Nums[Row] [Col]<<“ ”;

}

OutFile << endl;

}

OutFile.close( );

}

P. 709Pgrm. 12-4

slide25

Contents of File TABLE.TXT

2897 5 837

34 7 1623

390 3456 12

Pg. 709

slide26

#include <fstream>#include <iostream> using namespace std;

bool openFileIn(fstream &, char [51]);void showContents(fstream &);

int main()

{ fstream dataFile;

if (!openFileIn(dataFile,”demofile.txt);

{ cout << “File open error!<< endl;

return 0; }

P. 710-711Pgrm. 12-5

slide27

cout << “File opened successfully.\n”;

cout << “Now reading information from the file.\n\n”; showContents(dataFile);

cout << “done” ; return 0; // end of main}bool openFileIn(fstream &file, char *name){ bool status; file.open(name,ios::in);

if (file.fail())

status = false; else status = true;

return status; }

P. 711Pgrm. 12-5

slide28

void ShowContents(fstream &File)

{ char Name [81];

while (!File.eof( )) {

File >> Name;

cout << Name << endl;

}

P. 711Pgrm. 12-5

slide29

r

u

M

p

y

y

n

h

4

7

a

J

e

\n

C

i

r

l

o

n

c

A

J

e

e

s

\n

N

C

2

o

n

7

0

m

l

d

,

8

P. 712

2

\n

<EOF>

slide30

#include <fstream> #include <iostream>using namespace std;

int main()

{ fstream NameFile;

char Input[81];

NameFile.open(“murphy.txt”, ios::in);

if (NameFile == 0)

{

cout << “File open error!” << endl;

return 0;

} nameFile.getline(input,81); while (!NameFile.eof( ))

{ cout << Input; nameFile.getline(input,81); }

NameFile.close( );

}

P. 717Pgrm. 12-8

exercise
Exercise
  • Write a program that will read all the data in a file and write all the data to a new file removing the blanks.Modify page 730
slide32

#include <fstream> #include <iostream> int main()

{ fstream inFile;

ostream outFile(“out.dat”, ios:: out);

char Ch, FileName [51];

cout << “Enter the name of the file”;

cin >> FileName;

inFile.open(FileName, ios::in);

if (!inFile)

{ cout << FileName << “could not” << “be opened.\n”;

return 0;}

P. 723-724Pgrm. 12-12

slide33

// prime read inFile.get(ch); while (!inFile.eof( ))

{ if(Ch! = ‘ ‘ ) // change from textbook

outFile.put(Ch); inFile.get(Ch);

}

File.close( );

return 0;}

P. 723-724Pgrm. 12-12

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