File Processing

File processing function

Function	Description
fopen()	open a new or existing file
fprintf()	write data to file
fscanf()	read data from a file
fputc()	write a character to file
fgetc()	read a character from a file
fclose()	close the file
fseek()	set the file pointer to the given position
fputw()	Write an integer to a file
fgetw()	read an integer from a file
ftell()	returns the current position
rewind()	set the file pointer to the beginning of the file

There are many functions in the C library to open/read/write/search and close files

Open mode parameter

Mode	Description
r	Open a text file in read mode, allowing the file to be read
w	Open a text file in write mode, allowing writing to the file
a	Open a text file in append mode If the file does not exist, a new one will be created
r+	Open a text file in read-write mode, allowing reading and writing of the file
w+	Open a text file in read-write mode, allowing reading and writing of the file
a+	Open a text file in read-write mode, allowing reading and writing of the file
rb	Open a binary file in read mode
wb	Open binary file in write mode
ab	Open a binary file in append mode
rb+	open binary file in read-write mode
wb+	Open binary file in read-write mode
ab+	open binary file in read-write mode

Open the file: fopen()

#include <stdio.h>

void main() {
  FILE *fp;
  char ch;

  fp = fopen("file_handle.c", "r");

  while (1) {
    ch = fgetc(fp);
    if (ch == EOF)
      break;
    printf("%c", ch);
  }
  fclose(fp);
}

After performing all operations on the file, the file must be closed with fclose()

Write to file: fprintf()

#include <stdio.h>

void main() {
  FILE *fp;
  fp = fopen("file.txt", "w"); // open the file

  // write data to file
  fprintf(fp, "Hello file for fprintf..\n");
  fclose(fp); // close the file
}

Read the file: fscanf()

#include <stdio.h>

void main() {
  FILE *fp;

  char buff[255]; // Create a char array to store file data
  fp = fopen("file.txt", "r");

  while(fscanf(fp, "%s", buff) != EOF) {
    printf("%s ", buff);
  }
  fclose(fp);
}

Write to file: fputc()

#include <stdio.h>

void main() {
  FILE *fp;
  fp = fopen("file1.txt", "w"); // open the file
  fputc('a',fp); // write a single character to the file
  fclose(fp); // close the file
}

Read the file: fgetc()

#include <stdio.h>
#include <conio.h>

void main() {
  FILE *fp;
  char c;

  clrscr();

  fp = fopen("myfile.txt", "r");

  while( (c = fgetc(fp) ) != EOF) {
    printf("%c", c);
  }
  fclose(fp);

  getch();
}

Write to file: fputs()

#include<stdio.h>
#include<conio.h>

void main() {
  FILE *fp;

  clrscr();

  fp = fopen("myfile2.txt","w");
  fputs("hello c programming",fp);
  fclose(fp);

  getch();
}

Read files: fgets()

#include<stdio.h>
#include<conio.h>

void main() {
  FILE *fp;
  char text[300];

  clrscr();

  fp = fopen("myfile2.txt", "r");
  printf("%s", fgets(text, 200, fp));
  fclose(fp);

  getch();
}

fseek()

#include <stdio.h>

void main(void) {
  FILE *fp;

  fp = fopen("myfile.txt","w+");
  fputs("This is Book", fp);

  // Set file pointer to the given position
  fseek(fp, 7, SEEK_SET);

  fputs("Kenny Wong", fp);
  fclose(fp);
}

Set the file pointer to the given position

rewind()

#include <stdio.h>
#include <conio.h>

void main() {
  FILE *fp;
  char c;

  clrscr();

  fp = fopen("file.txt", "r");

  while( (c = fgetc(fp) ) != EOF) {
    printf("%c", c);
  }

  rewind(fp); // move the file pointer to the beginning of the file

  while( (c = fgetc(fp) ) != EOF) {
    printf("%c", c);
  }
  fclose(fp);

  getch();
}
// output
// Hello World! Hello World!

ftell()

#include <stdio.h>
#include <conio.h>

void main () {
   FILE *fp;
   int length;

   clrscr();

   fp = fopen("file.txt", "r");

   fseek(fp, 0, SEEK_END);
   length = ftell(fp); // return current position
   fclose(fp);

   printf("File size: %d bytes", length);

   getch();
}
// output
// file size: 18 bytes

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