(Text File)

File connection

(Text File)

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■ File types

■ Opening files

■ Closing files

■ Reading from files

■ Writing to files

■ File pointer manipulations

■ Files deletion and rename

Topics

Why programming with files

■ Files can save all information once the program terminated

■ Results from your program can easily saved into files

■ Input bulk data from keyboard input can be the

most tedious job to do

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■ Streams are flows of information

■ File is one type of stream to either receive or send information

■ Stream type

■ Text Streams

■ Binary Streams

Streams

■ Text Streams

■ Storing data in a form of ASCII

■ New line can be stored using additional ASCII codes

■ Carriage-return

■ Linefeed

■ Example files are .c, .txt, .bat

■ Binary Streams

■ Storing each data in 1 byte

■ Example files type are .exe, .com, .obj

■ EOF is used to end the files which can be checked

Streams

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File manipulation

■ Orders of manipulation

■ Open the files

■ Files read/write/etc.

■ Closing the files

■ A pointer will be used to identify a file to be used for

reading/writing.

File declaration

■ FILE data type similar to int, char

■ *fp a variable name of a file

FILE *fp;

Since C is case sensitive, all letter of the word “FILE “ are required to be capitalised.

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Opening the file

■ fp the name of a file pointer (after declaring FILE *fp;)

■ fopen A file opening command

■ file name Name (and extension) of a file you will use

■ mode Mode in which to used the file for, e.g. read, write

fp = fopen(“file name”,“mode”);

■ fopen() in stdio.h usage

FILE *fopen(char *fname,char *mode);

Example

FILE *fp;

if ((fp = fopen("myfile","r")) == NULL) { printf("Error opening file \n");

exit(1);

}

Managing a File

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Mode How it works

r Opening the text file for reading only

w Opening the text file for writing. If the file exists, the will be replaced.

a Appending(add to the end) the text file. The file will be created if not exist.

r+ Opening the text file for reading and writing

w+ Opening the text file for writing. If the file exists, the will be replaced.

a+ Appending(add to the end) the text file. The file will be created if not exist.

Managing a File

For Text File, the letter“t” เพิมเข้าไปใน mode ด้วย (rt, w+t เป็นต้น)

สําหรับการทํางานกับ Binary File เราต้องใส่อักษร “b” เพิมเข้าไปใน mode ด้วย (wb, a+b เป็นต้น)

■ NULL will be returned if the file cannot be opened

■ fclose() is used for closing the file (stdio.h)

int fclose(FILE *fp)

■ remove() is used for deleting the file

int remove(char *file-name)

■ rename() is used for changing the file name

int rename(char *oldname, char *newname)

Managing a File

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Commands for text files

■ Read/Write 1 Byte at a time to a file

int fgetc(FILE *fp)

int fputc(int ch, FILE *fp)

■ Read/write more than 1 Byte

char *fgets(char *str, int num, FILE *fp) int fputs(char *str, FILE *fp)

int fprintf(FILE *fp, char *cont_string,..)

int fscanf(FILE *fp, char *cont_string,..)

Example

char name[20];

■ mode "r"

name[0]=fgetc(fp);

fgets(name,19,fp);

fscanf(fp,"%s",name);

■ mode "w" ,"a"

fputc(name[0],fp);

fputs(name,fp);

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Reading from a text file

■ fscanf Command

■ fp File pointer

■ fname The first string will be strored in the variable

■ lname The second string(after a white space) will be stored here

fscanf (fp, "%s %s", fname, lname);

Reading from a text file

■ Jakkapan will be in fname

■ Madeetrakul will be in lname

fscanf (fp, "%s %s", fname, lname);

In this case, strings from an example file will be stored as followed

Jakkapan Madeetrakul

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Writing a Text File

fprintf (fp, "%s %d", name, age);

Writing to a Text File

fprintf (fp, "%s %d", name, age);

In this example if name is having the value “Teera” while age is 30 A text file will be

Teera 30

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Writing to a Text File

After writing to a text file all data types(int,float) will becom strings

fprintf (fp, "%s\t%d", name, age);

For example

Text file will become

Teera 30

*****Reading and writing requires the same format type*****

Experiment of writing a text file

■ An example program can be done by

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■ Entering a text file by inserting name,age,gpa in a text file

■ Run a program again to see the result

Writing a data on a text file

Reading a text file and print on the

screen

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#include "stdio.h"

#include "stdlib.h"

char str[80] = "This is a file system test"; /* text for writing*/

void main() {

FILE *fp;

char *p;

if ((fp = fopen("myfile.txt","w"))==NULL) { /* opening myfile for writing*/

printf("Can not open file.");

exit(1);

}

p = str; /* p points to str*/

while (*p) { /* loop for writing*/

if (fputc(*p,fp)==EOF) { /* Write each Byte to the file */

printf("Error writing file\n");

exit(2);

}

p++; /* move Pointer p one position at a time*/

}

fclose(fp); /* closing file*/

}

Example Using fputc to write"This is a file system test" to myfile

#include "stdio.h"

#include "stdlib.h"

void main() {

FILE *fp;

int i;

if ((fp = fopen("myfile.txt","r"))==NULL) { /* opening myfile for reading */

printf("Can not open file.");

exit(1);

}

for(;;) { /* loop*/

i = fgetc(fp); /* read each byte to i*/

if(i==EOF) break; /* read till the end*/

putchar(i); /* Print to the screen*/

ต ัวอย่าง Using fgetc to read myfile

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#include "stdlib.h"

#include "stdio.h"

void main(void) {

int i;

FILE *fp;

if ((fp = fopen("test.txt", "w"))==NULL) { printf("File could not be opened.");

exit(1);

}

for (i=1;i<=10;i++)

fprintf(fp, "this is a test %d * %d = %d\n", i, i, i*i);

fclose(fp);

}

ต ัวอย่าง Writing to test

Writing to a file

■ 1

■ 3

■ 6

■ 10

■ 15

■ …

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#include "stdlib.h"

#include "stdio.h"

void main(void) { char str[81];

FILE *fp;

if ((fp = fopen("test.txt","r"))==NULL) { printf("File could not be opened.");

exit(1);

}

while (!feof(fp)) {

if (fgets(str,80,fp)) printf("%s", str);

}

fclose(fp);

}

Example Reading from a file test.txt and print to the screen

#include "stdio.h"

void main() {

int account;

charname[30];

float balance;

FILE *cfPtr;

if ((cfPtr = fopen("client.dat","w"))==NULL) { printf("File could not be opened.");

} else {

printf("Enter the account ,name and balance \n ctrl+z for exit.\n");

printf("? ");

scanf("%d%s%f", &account, name, &balance);

while (!feof(stdin)) { /* stdin คือแปมพิมพ

และ ctrl+z คือบอกสิ้นสุดการปอนขอมูล*/

fprintf(cfPtr,"%d %s %.2f\n", account, name, balance);

printf("? ");

scanf("%d%s%f", &account, name, &balance);

}

fclose(cfPtr);

Example reading from the screen and put in a text file

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#include "stdio.h"

void main() {

int account;

char name[30];

float balance;

FILE *cfPtr;

if ((cfPtr = fopen("client.dat","r"))==NULL) { printf("File could not be opened.");

} else {

printf("%-10s %-13s %s\n", "Account", "Name", "Balance");

fscanf(cfPtr,"%d%s%f", &account, name, &balance);

while (!feof(cfPtr)) {

printf("%-10d %-13s %7.2f\n", account, name, balance);

fscanf(cfPtr, "%d%s%f", &account, name, &balance);

}

fclose(cfPtr);

}

return;

}

ต ัวอย่าง Read file from client

Question ?