input file dalam c++

Input/Output with files

Rena Widita

C++ provides the following classes to perform

output and input of characters to/from files:

• ofstream: Stream class to write on files

• ifstream: Stream class to read from files

• fstream: Stream class to both read and

write from/to files.

• These classes are derived directly or

indirectly from the classes istream, and

ostream.

Baca Tulis File

Untuk dapat membaca atau menulis data dari/ke sebuah file maka

langkah yang perlu dilakukan adalah:

1. membuka file

- mendefinisikan variabel stream

- melakukan perintah open()

2. Melakukan pembacaan atau penulisan data

- menggunakan operand << atau >>

- menggunakan operand read() atau write()

perintah read() atau write() -> informasi ukuran data

yang akan dibaca atau ditulis sangat penting

3. Menutup file

- menggunakan perintah close()

This code creates a file called example.txt and inserts a sentence into it in the same

way we are used to do with cout, but using the file stream myfile instead.

All these flags can be combined using the bitwise operator OR (|). For example, if we want to

open the file example.bin in binary mode to add data we could do it by the following call to

member function open():

Each one of the open() member functions of the classes ofstream, ifstream and fstream has a

default mode that is used if the file is opened without a second argument:

Where filename is a null-terminated character sequence of type const char * (the same type that

string literals have) representing the name of the file to be opened, and mode is an optional

parameter with a combination of the following flags:

to open a file with a stream object we use its member function open():

open (filename, mode);

• For ifstream and ofstream classes, ios::in and ios::out are automatically and respectively assumed, even if a mode that does not include them is passed as second argument to the open() member function.

The default value is only applied if the function is called without specifying any value for the mode parameter. If the function is called with any value in that parameter the default mode is overridden, not combined.

File streams opened in binary mode perform input and output operations independently of any format considerations. Non-binary files are known as text files, and some translations may occur due to formatting of some special characters (like newline and carriage return characters).

Since the first task that is performed on a file stream object is generally to open a file, these three classes include a constructor that automatically calls the open() member function and has the exact same parameters as this member. Therefore, we could also have declared the previous myfile object and conducted the same opening operation in our previous example by writing:

ofstream myfile ("example.bin", ios::out | ios::app | ios::binary);

• Combining object construction and stream opening in a single statement. Both forms to open a file are valid and equivalent.

To check if a file stream was successful opening a file, you can do it by calling to member is_open() with no arguments. This member function returns a bool value of true in the case that indeed the stream object is associated with an open file, or false otherwise:

if (myfile.is_open()) { /* ok, proceed with output */ }

Closing a file

• When we are finished with our input and output operations on a file we shall close it so that its resources become available again.

• We have to call the stream's member function close(). This member function takes no parameters, and what it does is to flush the associated buffers and close the file:

myfile.close();

Once this member function is called, the stream object can be used to open another file, and the file is available again to be opened by other processes.

In case that an object is destructed while still associated with an open file, the destructor automatically calls the member function close().

Text files

• Text file streams are those where we do not include the ios::binary flag in their opening mode.

• These files are designed to store text and thus all values that we input or output from/to them can suffer some formatting transformations, which do not necessarily correspond to their literal binary value.

Data output operations on text files are performed in the same way we operated with cout:

Data input from a file can also be performed in the same way that we did with cin:

This last example reads a text file and prints out its content on the screen. Notice

how we have used a new member function, called eof() that returns true in the case

that the end of the file has been reached. We have created a while loop that finishes

when indeed myfile.eof() becomes true (i.e., the end of the file has been reached).

Checking state flags

• In addition to eof(), which checks if the end of file has been reached, other member functions exist to check the state of a stream (all of them return a bool value):

• bad()– Returns true if a reading or writing operation fails. For example in the case that we try to write

to a file that is not open for writing or if the device where we try to write has no space left.

• fail()– Returns true in the same cases as bad(), but also in the case that a format error happens,

like when an alphabetical character is extracted when we are trying to read an integer number.

• eof()– Returns true if a file open for reading has reached the end.

• good()– It is the most generic state flag: it returns false in the same cases in which calling any of the

previous functions would return true.

•

In order to reset the state flags checked by any of these member functions we have just seen we can use the member function clear(), which takes no parameters.

get and put stream pointers

• All i/o streams objects have, at least, one internal stream pointer:

ifstream, like istream, has a pointer known as the get pointer that points to the element to be read in the next input operation.

ofstream, like ostream, has a pointer known as the put pointer that points to the location where the next element has to be written.

Finally, fstream, inherits both, the get and the put pointers, from iostream (which is itself derived from both istream and ostream).

These internal stream pointers that point to the reading or writing locations within a stream can be manipulated using the followingmember functions:

Contoh program membuka

dan menutup file:

#include <iostream>

#include <fstream>

using namespace std;

void main() {

// Mendeklarasikan stream untuk proses input

ifstream VarBaca;

// membuka file

VarBaca.open("COBA.TXT");

// Menutup file

VarBaca.close();

}

Baca Tulis File

Baca Tulis File

#include <iostream>

#include <fstream>


void main() {

// Mendeklarasikan stream untuk proses output

ofstream VarTulis;

// membuka file

VarTulis.open("COBA.TXT");

VarTulis << “C++ mudah Sekali” << endl;;

VarTulis << “Pemrograman Mudah “ << endl;

// Menutup file

VarTulis.close();

}

Contoh program menulis

data ke file:Data file yang bernama

“COBA.TXT” akan disimpan pada

folder di mana folder tempat

program file berada. Atau informasi

drive dan folder harus diinputkan,

contoh:

“C://DATA//COBA.TXT”

Jika file “Coba.txt” kita buka

dengan editor notepad, akan

tampak seperti:

Melakukan penulisan data ke dalam file

- menggunakan operand <<

Melakukan pembacaan data dari file

- menggunakan operand >>

Baca Tulis File

#include <iostream>

#include <fstream>


void main() {


ifstream VarBaca;

char Teks[80];

// membuka file


VarBaca >> Teks; // proses membaca data dr file (1 string/kata)

cout << Teks << “ “; // “ “ -> memisahkan dg teks berikutnya

VarBaca >> Teks; // proses baca data dr file (1 string/kata)

cout << Teks;

// Menutup file

VarBaca.close();

}

Contoh program membaca

data dari file:

Data file yang bernama

“COBA.TXT” harus sudah

ada di folder tempat program file

berada. Jika tidak maka informasi


contoh:


VarBaca >> Teks; menghasilkan

satu string/kata dibaca dari file.

Jika coba.txt hasil dari program slide

sebelumnya adalah sebagai input

file maka hasil dilayar adalah:

Baca Tulis File


- menggunakan operand >> dan while()

#include <iostream>

#include <fstream>


void main() {


ifstream VarBaca;

char Teks[80];

// membuka file


while(VarBaca.good()) // apakah berhasil membuka

{ // file atau tidak

VarBaca >> Teks; // proses membaca data dr file

cout << Teks;

}

// Menutup file

VarBaca.close();

}


data dari file:

Data file yang bernama

“COBA.TXT” harus sudah

ada di folder tempat program file

berada. Jika tidak maka informasi


contoh:


VarBaca.good() :

“true” jika berhasil membuka

file/membaca data file, “false” jika

tidak berhasil membuka

file/membaca data file.

Hasil:

Baca Tulis File

#include <iostream>

#include <fstream>


void main() {


ofstream VarTulis;

char Teks[80];

// membuka file

VarTulis.open("COBA.TXT");

strcpy(Teks, “Kalimat Pertama”);

VarTulis.write(Teks, 15); // proses menulis data ke file

cout << Teks;

strcpy(Teks,”Kalimat Kedua”);

VarTulis.write(Teks, 13); // proses tulis data ke file

cout << Teks;

// Menutup file

VarTulis.close();

}

Melakukan penulisan data ke dalam file

- menggunakan operand write()


data ke file:

VarTulis.write(Teks, 15); adalah

proses menulis data ke file berupa

string yang tersimpan dalam variabel

Teks sebanyak 15 byte. String

“Kalimat Pertama” terdiri dari 15

karakter.

Hasil:

Silahkan dicoba jika angka 15 diganti

dengan angka yang berbeda!

Sintaks: basic_istream::write (char * buffer, bytesize n);

Baca Tulis File

#include <iostream>

#include <fstream>


void main() {


ifstream VarBaca;

char Teks[80];

// membuka file


strcpy(Teks, " "); // mengosongkan variabel Teks

VarBaca.read(Teks, 15); // proses membaca data dr file

cout << Teks << endl;

strcpy(Teks, " "); // mengosongkan variabel Teks

VarBaca.read(Teks, 13); // proses baca data dr file

cout << Teks;

// Menutup file

VarBaca.close();

}


- menggunakan operand read()

Sintaks: basic_istream::read (char * buffer, bytesize n);


data ke file:

Jika coba.txt hasil dari program slide

sebelumnya adalah sebagai input file

maka hasil dilayar adalah:

Silahkan dicoba jika angka 15

atau 13 diganti dengan angka

yang berbeda!

Melakukan penulisan data berupa numerik

- menggunakan operand write()

Baca Tulis File

#include <iostream>

#include <fstream>


void main() {


ofstream VarTulis;

float angka = 23.3;

// membuka file

VarTulis.open("COBA.dat");

VarTulis.write((char *) &angka, sizeof(float));

// Menutup file

VarTulis.close();

}


data ke file:

Hasil penyimpanan data numerik ke

file adalah berupa data biner.

Jika file “Coba.dat” dibuka

menggunakan editor notepad, maka

akan tampak seperti:

Melakukan pembacaan data numerik

- menggunakan operand read()

Baca Tulis File

#include <iostream>

#include <fstream>


void main() {


ifstream VarBaca;

float angka;

// membuka file

VarBaca.open("COBA.dat");

VarBaca.read((char *) &angka, sizeof(float));

cout << angka << endl;

// Menutup file

VarBaca.close();

}


data dari file:

Jika file “coba.dat” hasil dari

program slide sebelumnya adalah

sebagai input file maka hasil

dilayar adalah:

Silahkan dicoba menyimpan

data berupa angka/numerik

lebih dari satu dengan jenis

tipe data yang berbeda (mis.

Int, long int, double) ! Dan

anda pikirkan bagaimana

cara membaca data yang

telah tersimpan tersebut. !!

Baca Tulis File

#include <iostream>

#include <fstream>

using namespace std;void main(void) {


ifstream VarBaca;


ofstream VarTulis;

char Teks[80];

// membuka file

VarTulis.open("COBI.TXT");

VarTulis << " C++ mudah Sekali " << endl; //menulis data ke file

VarTulis << " Pemrograman Mudah " << endl; //menulis data ke file

// Menutup file

VarTulis.close();

Contoh program menulis dan membaca data ke/dari file:

Contoh penggunaan property getline dan eof dlm pembacaan data

istream& getline( char* pch, int nCount, char delim = '\n' );

Hasil penyimpan di file:

Baca Tulis File

// membuka file

VarBaca.open("COBI.TXT");

//membaca seluruh data dari file, baris per baris

while (!VarBaca.eof()) {

VarBaca.getline(Teks,80, '\n'); //membaca data dari file


}

// Menutup file

VarBaca.close();

}

Lanjutan $

VarBaca.eof() memberikan harga “bukan nol” jika akhir suatu file

telah ditemukan.

VarBaca.getline(Teks,80, '\n'); membaca data karakter yang tersimpan pada file

sampai tanda delimiter ditemukan, delimited ‘\n‘ berarti membaca karakter sampai tanda

pindah baris ditemukan.

Coba tanda delimiter ‘\n’ anda ganti dengan tanda delimiter spcebar ‘ ‘. Perhatikan hasil

pada layar.

Hasil pembacaan dari file:

delimiter ‘\n’ diganti dengan spacebar ‘ ‘, hasil:

Baca Tulis File

#include <iostream>

#include <fstream>


void main(void) {


ifstream VarBaca;


ofstream VarTulis;

char Teks[80];

// membuka file

VarTulis.open("COBE.TXT");

VarTulis << "C++ sangat Sekali" << endl; //menulis data ke file

VarTulis << "Pemrograman Mudah" << endl; //menulis data ke file

// Menutup file

VarTulis.close();

Contoh program menulis dan membaca data ke/dari file dg fstream:

Contoh penggunaan property seekg dlm pembacaan data

Baca Tulis FileLanjutan $

// membuka file

VarBaca.open("COBI.TXT");

VarBaca.seekg(17, ios::beg); // set file pointer ke posisi

// 17byte dr awal file

Strcpy(Teks, “ “);


cout << Teks << “ “;


// 0byte dr awal file




VarBaca.seekg(28, ios::cur); // set file pointer ke posisi

// 28byte dr posisi saat itu





// 10byte dr posisi awal




// Menutup file

VarBaca.close();

}

Baca Tulis FileLanjutan $

Hasil:

Baca Tulis File

Membaca atau menulis data dari/ke sebuah file dapat dilakukan juga

dengan perintah fopen()

Untuk dapat membaca atau menulis data dari/ke sebuah file maka

langkah yang perlu dilakukan adalah:

1. membuka file

- mendefinisikan variabel stream

- melakukan perintah fopen()

2. Melakukan pembacaan atau penulisan data

- menggunakan operand fscanf() atau fprintf()

- menggunakan operand fread() atau fwrite()

perintah fread() atau fwrite() -> informasi ukuran data

yang akan dibaca atau ditulis sangat penting

3. Menutup file

- menggunakan perintah fclose() atau _fcloseall();

Contoh program membuka

dan menutup file:

Baca Tulis File

#include <iostream.h>

#include <stdio.h>

#include <stdlib.h>

void main() {

// Mendeklarasikan stream untuk proses inputFILE *VarBaca;

// membuka fileVarBaca = fopen("COBA.TXT", "r");

if(VarBaca==NULL){

cout << " Error buka file : " << "Coba.txt"

<< endl;

exit(-1); // keluar dari program}

// Menutup filefclose(VarBaca);

}

Baca Tulis File


#include <stdio.h>

#include <stdlib.h>

void main() {

// Mendeklarasikan stream untuk proses inputFILE *VarTulis;

// membuka fileVarTulis = fopen("COBA.TXT", "w");

if(VarTulis==NULL){

cout << " Error buka file : " << "Coba.txt“ << endl;

exit(-1);

}

fprintf(VarTulis,"C++ mudah Sekali\n");

fprintf(VarTulis,"Pemrograman Mudah");

// Menutup filefclose(VarTulis);

}

Contoh program

menulis data ke file:

Melakukan pembacaan atau penulisan data

- menggunakan operand fprintf() atau fscanf()

Baca Tulis File


#include <stdio.h>

#include <stdlib.h>

void main() {


FILE *VarBaca;

char Teks[80];

// membuka file

VarBaca = fopen("COBA.TXT", "r");

if(VarBaca==NULL){


exit(-1);

}

while(fscanf(VarBaca,"%s",Teks)!=EOF) {


}

// Menutup file

fclose(VarBaca);

}

Contoh program

membaca data ke

file:


- menggunakan operand fprintf() atau fscanf()

Baca Tulis File


- menggunakan operand fprintf() atau fscanf() dan fgets()


#include <stdio.h>

#include <stdlib.h>

#include <string.h>

void main() {


FILE *VarTulis, *VarBaca;

char Teks[80];

// membuka file

VarTulis = fopen("COBA.TXT", "w");

if(VarTulis==NULL){


<< endl;

exit(-1);

}

Baca Tulis File

strcpy(Teks, "Kalimat Pertama");

fprintf(VarTulis,"%20s", Teks); // proses menulis data ke file

cout << Teks;

strcpy(Teks, "Kalimat Kedua");


cout << Teks;

// Menutup file

fclose(VarTulis);

Lanjutan $



Baca Tulis File

// membuka file


if(VarBaca==NULL){


<< endl;

exit(-1);

}

while( fgets(Teks, 21, VarBaca) != NULL ) {


}

// Menutup file

fclose(VarBaca);

}

Lanjutan $



Baca Tulis File


#include <stdio.h>

#include <stdlib.h>

#include <string.h>

void main() {


FILE *VarTulis;

char Teks[80];

// membuka file


if(VarTulis==NULL){


<< endl;

exit(-1);

}




data ke file:

Sintaks: fwrite (char * buffer, size t, count n, iobuf *);

Baca Tulis File

// membuka file


fwrite(Teks,sizeof(char),20, VarTulis); // proses menulis data ke file

cout << Teks;


fwrite(Teks,sizeof(char),20, VarTulis); // proses menulis data ke file

cout << Teks;

// Menutup file

fclose(VarTulis);

}



Contoh program menulis data ke file:

Sintaks: fwrite (char * buffer, size t, count n, iobuf *);

Lanjutan$.

Baca Tulis File


#include <stdio.h>

#include <stdlib.h>

#include <string.h>

void main() {


FILE *VarBaca;

char Teks[80];

// membuka file


if(VarBaca==NULL){


<< endl;

exit(-1);

}



Contoh program

Membaca data ke file:

Sintaks: fread (char * buffer, size t, count n, iobuf *);

Baca Tulis File

fread(Teks,sizeof(char),20, VarBaca); // proses menulis data ke file


fread(Teks,sizeof(char),20, VarBaca); // proses menulis data ke file


// Menutup file

fclose(VarBaca);

}



Contoh program

Membaca data ke file:

Sintaks: fread (char * buffer, size t, count n, iobuf *);

Lanjutan$.


- menggunakan operand fwrite()

Baca Tulis File


#include <stdio.h>

#include <stdlib.h>

void main() {

// Mendeklarasikan stream untuk proses inputFILE *VarTulis;

float angka = 23.3;

// membuka fileVarTulis = fopen("COBA.DAT", "w");

if(VarTulis==NULL){


exit(-1);

}

fwrite(&angka,sizeof(float),1, VarTulis); // proses menulis data ke file


// Menutup file

fclose(VarTulis);

}

Contoh program

Menulis data ke file:


- menggunakan operand fwrite()

Baca Tulis File


#include <stdio.h>

#include <stdlib.h>

void main() {


FILE *VarBaca;

float angka;

// membuka file

VarBaca = fopen("COBA.DAT", "r");

if(VarBaca==NULL){

cout << " Error buka file : " << "Coba.txt" << endl;

exit(-1);

}

fread(&angka,sizeof(float),1, VarBaca); // proses menulis data ke file


// Menutup file

fclose(VarBaca);

}

Contoh program

Menulis data ke file:

Baca Tulis File


- menggunakan operand fread() atau fwrite() dan fungsi fseek()


#include <stdio.h>

#include <stdlib.h>

#include <string.h>

void main() {


FILE *VarTulis, *VarBaca;

char Teks[80];

// membuka file


if(VarTulis==NULL){


<< endl;

exit(-1);

}

Baca Tulis File





cout << Teks;



cout << Teks;

// Menutup file

fclose(VarTulis);

Lanjutan$.

// membuka file


if(VarBaca==NULL){


<< endl;

exit(-1);

}

while( fgets(Teks, 21, VarBaca) != NULL ) {


}

fseek(VarBaca, -40, SEEK_END);

fgets(Teks, 21, VarBaca);

// Menutup file

fclose(VarBaca);

}

Baca Tulis File



Lanjutan$.