Transcript File Handling - Gadjah Mada University

File Handling
Pemrograman File
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Membuat suatu file baru
Membuka suatu file
Menutup suatu file
Membaca suatu file
Menutup suatu file
Lingkup file
• Secara umum pada C, semua piranti
komputer bisa dianggap sebagai ‘file’
• Lingkup file yang akan dibahas pada
materi ini:
– Kumpulan data yang disimpan pada media
penyimpan (disk)
Text & Binary File
• Text file  hanya berisi teks, terdiri dari
karakter-karakter ascii, tanpa ada formatting.
Contoh: file teks(dibuat pakai notepad), file
source code
• Binary file  berisi data biner, baik berupa data
ascii maupun formatting. Contoh : file MS word
(ada teks dan formatting:cetak tebal,cetak
miring,tabel dsb)
• Cara menentukan file teks/biner: buka file tsb
pakai notepad(teks editor),kalau file tsb bisa
dibaca, berarti file teks. kalau tidak(tidak
beraturan), berarti file biner
Bagaimana kita memperlakukan
file di C:
DISK
Proses open file:
Membuat link antara
File dgn pointer to file
link
File yg tersimpan
di disk
MEMORI
Pointer to File :
Alokasi
Memori komputer
Utk memproses
file
Proses close file:
Memutus link file - pointer
File handling in C
• In C we use FILE * to represent a pointer to a
file.
• fopen is used to open a file. It returns the
special value NULL to indicate that it couldn't
open the file.
FILE *fptr;
char filename[]= "file2.dat";
fptr= fopen (filename,"w");
if (fptr == NULL) {
fprintf (stderr,
“ERROR”);
/* DO SOMETHING */
}
Opening a File
• A file must be “opened” before it can be used.
FILE *fp;
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:
fp = fopen (filename, mode);
fp is declared as a pointer to the data type FILE.
filename is a string - specifies the name of the file.
fopen returns a pointer to the file which is used in all
subsequent file operations.
mode is a string which specifies the purpose of
opening the file:
“r” :: open the file for reading only
“w” :: open the file for writing only
“a” :: open the file for appending data to it
Fungsi fopen
• Berfungsi membuat link antara file (umumnya di
disk) dengan memori (pointer to file)
• Format: pointer_to file = fopen(namafile,mode) ;
• Jika namafile sudah ada, maka komputer tinggal
membuat link saja
• Jika namafile belum ada, maka komputer akan
membuat (create) file tersebut dahulu
Modes for opening text files
• The second argument of fopen is the
mode in which we open the text file.
There are three
• "r" opens a file for reading(read only!)
• "w" creates a file for writing - and writes
over all previous contents (deletes the file
so be careful! previous contents are
erased)
• "a" opens a file for appending - writing on
the end of the file
Other modes
• “r+” : open text file for read/write
• “w+” : create text file for read/write
• “a+” : append to or create a text file for
read/write
Gambaran efek masing2 mode
pada suatu file teks
Sebelum fopen
abcdefghi
Sebelum fopen
abcdefghi
w,w+
(ada isinya)
a,a+
Setelah fopen
abcdefghi
(kosong)
Sebelum fopen
abcdefghi
Setelah fopen
r,r+
Setelah fopen
abcdefghi
Pointer file
Ada disini
Pointer file
Ada disini
Closing a File
• After all operations on a file have been
completed, it must be closed.
– Ensures that all file data stored in memory buffers are
properly written to the file.
• General format: fclose (file_pointer) ;
FILE *xyz ;
xyz = fopen (“test”, “w”) ;
…….
fclose (xyz) ;
Writing to a file using fprintf
• fprintf works just like printf and sprintf
except that its first argument is a file
pointer.
FILE *fptr;
fptr= fopen ("file.dat","w");
/* Check it's open */
fprintf (fptr,"Hello World!\n");
fclose(fptr);
Percobaan
• Buat sembarang file teks dengan notepad dan
namai file tsb dengan nama “file.dat”
• Isilah file tsb dengan sembarang karakter
misalnya “abcbdef……”
• Buatlah program seperti pada slide sebelumnya
• Letakkan file teks tsb satu folder dengan
program
• Eksekusi program tsb, buka file.dat dengan
notepad apa yg terjadi dengan isi file nya?
• Gantilah dengan mode yang lain, amati hasilnya
Reading from a file using fgets
• fgets is a better way to read from a file
• We can read into a string using fgets
FILE *fptr;
char line [1000];
/* Open file and check it is open */
while (fgets(line,1000,fptr) != NULL) {
printf ("Read line %s\n",line);
}
fgets takes 3 arguments, a string, a maximum
number of characters to read and a file pointer.
It returns NULL if there is an error (such as EOF)
fscanf and fprintf
• We can also use the file versions of scanf
and printf, called fscanf and fprintf.
• General format:
fscanf (file_pointer, control_string, list) ;
fprintf (file_pointer, control_string, list) ;
• Examples:
fscanf (fp, “%d %s %f”, &roll, dept_code, &cgpa) ;
fprintf (out, “\nThe result is: %d”, xyz) ;
Other Read/Write Operations on
Files
• The simplest file input-output (I/O) function are getc and
putc.
• getc is used to read a character from a file and return it.
char ch; FILE *fp;
…..
ch = getc (fp) ;
– getc will return an end-of-file marker EOF, when the end of the
file has been reached.
• putc is used to write a character to a file.
char ch; FILE *fp;
……
putc (c, fp) ;
Contoh soal
• Buatlah program untuk meng-convert
huruf-huruf pada suatu text file menjadi
uppercase!
Example :: convert a text file to all
UPPERCASE
main() {
FILE *in, *out ;
char c ;
in = fopen (“infile.dat”, “r”) ;
out = fopen (“outfile.dat”, “w”) ;
while ((c = getc (in)) != EOF)
putc (toupper (c), out);
fclose (in) ;
fclose (out) ;
}
Checking EOF (end of file)
• How to check EOF condition when using
fscanf?
– Use the function feof
if (feof (fp))
printf (“\n Reached end of file”) ;
• How to check successful open?
– For opening in “r” mode, the file must exist.
if (fp == NULL)
printf (“\n Unable to open file”) ;
Contoh soal
• Buatlah program untuk menampung datadata mhs di suatu file teks. Data mhs
dibuat dalam bentuk struct yang terdiri
dari:
– Roll (kelas)
– Dept_code (NIM)
– GPA (IP)
Contoh soal
• Suatu file teks berisi data mahasiswa yang
merupakan suatu struktur data yang berisi:
– Roll (kelas)
– Dept_code (NIM)
– GPA (IP)
Buatlah program untuk menghitung IP rerata
dari data-data yang ada di file tsb!
Jawab
typedef struct {
int roll;
char dept_code[6];
float cgpa;
} STUD;
main() {
FILE *stud;
STUD s;
float sum = 0.0;
int count = 0;
stud = fopen (“stud.dat”, “r”) ;
while (1) {
if (feof (stud)) break;
fscanf (stud, “%d %s %f”, &s.roll,
s.dept_code, &s.cgpa);
count ++;
sum += s.cgpa;
}
printf (“\nThe average cgpa is %f”,
sum/count);
fclose (stud);
}
Binary File
• Binary files can not be created by an editor
(as with text files)
• A binary file is created by writing on it from
a C-program
Binary file fopen modes
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“rb” : open binary file for read
“wb” : create binary file for write
“ab” : append to a binary file
“r+b” : open binary file for read/write
“w+b” : create binary file for read/write
“a+b” : append to or create a binary file for
read/write
example
• Membuat suatu file biner untuk menampung
array bilangan integer kemudian membacanya
FILE *binaryp, *inbinp;
int i, list[255];
binaryp = fopen("nums.bin", "wb");//create file nums.bin
for (i = 2; i <= 500; i += 2)
fwrite(&i, sizeof (int), 1, binaryp);
fclose(binaryp);
/* read 250 integers into a vector */
inbinp = fopen(”nums.bin”,”rb”);//buka file nums.bin
fread(list, sizeof(int), 250, inbinp);
fclose(inbinp);