(Text File)

File connection

(Text File)

Topics

• File types

• Opening files

• Closing files

• Reading from files

• Writing to files

• File pointer manipulations

• Files deletion and rename

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

Streams

• Streams are flows of information

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

• Stream type

o Text Streams

o Binary Streams

Streams

• Text Streams

o Storing data in a form of ASCII

o New line can be stored using additional ASCII codes

• Carriage-return

• Linefeed

o Example files are .c, .txt, .bat

• Binary Streams

o Storing each data in 1 byte

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

• EOF is used to end the files which can be checked with an

File manipulation

• Orders of manipulation

o Open the files

o Files read/write/etc.

o 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.

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”);

Managing a File

• 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

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.

10

‘+’ mode can be used with rewind(fp);ter“t” เพิมเข้าไปใน mode ด้วย (rt, w+t เป็นต้น)

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

Managing a File

• 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)

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,..)

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

Reading numeric data will first be read as string and cast it to int/float later

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

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

• 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

typedef struct{

char name[20];

int age;

float gpa;

}stu;

void main(){

stu r[5];

FILE *fp;

char a[20];

fp = fopen("C:/Users/admin/Documents/1.txt","w");

for(int i=0;i<2;i++){

printf("Enter name:");

scanf("%s",r[i].name);

printf("Enter age:");

scanf("%d",&r[i].age);

printf("Enter gpa:");

scanf("%f",&r[i].gpa);

fprintf(fp,"%s %d %.2f\n",r[i].name,r[i].age,r[i].gpa);

}

Reading text from file and print on the screen

void main(){

stu r[5];

FILE *fp;

fp = fopen("C:/Users/admin/Documents/1.txt","r");

while(!feof(fp)){

fscanf(fp,"%s %d %f",r[0].name,&r[0].age,&r[0].gpa);

if(!feof(fp)) printf("%s %d %.2f\n",r[0].name,r[0].age,r[0].gpa);

}

Reading each character from file and print on the screen

void main(){

char a;

FILE *fp;

fp = fopen("C:/Users/admin/Documents/1.txt","r");

while(!feof(fp)){

a=fgetc(fp);

if(!feof(fp)) printf("%c”,a);

}

}

#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*/

Example Using fgetc to read myfile

Write each character to file

void main(){

char a[]=“Mahidol university”;

FILE *fp;

fp = fopen("C:/Users/admin/Documents/1.txt",“w");

for(int i=0;i<strlen(a);i++) fputc(a[i],fp);

}

#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 "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

• …

#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;

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

printf("? ");

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

}

Example reading from the screen and put in a text file

#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;

}

Example Read file from client

Question ?