File to create, write, read and append in c

File handling in c:

• So far, to write programs are done on command prompt or terminal (i.e. ubuntu os of cmd) which is not stored anywhere and most of the time we want to rewrite those programs.
• But now a day we are using GUI level so we can easily store data in files, write also can be open and read.
• If needs to store and fetched data in the file on your system, different operations are required to store by using ‘C’ language.

*Creation of a new file (fopen )

*Opening an existing file (fopen).

*Reading from file (fscanf or fgets).

*Writing to a file (fprintf or fputs).

*Moving to a specific location in a file (fseek, rewind).

*Closing a file (fclose).

• C provides the number of functions that help to perform basic file operations.
• File functions are,

• Also, need modes for writing or read a file:

How to Create a File:

• fopen is the standard function that is used to open a file.
• If the file is not present on the system, then it is created and then opened.
• If a file is already present on the system, then it is directly opened using this function.

Syntax:

 FILE *fp;

fp = fopen ("file_name", "mode");

where, fp is a pointer variable.

Example:

#include <stdio.h>

#include<conio.h>

int main() {

                      FILE *fp;

                      clrscr();

                      fp  = fopen ("welcome.txt", "w");//create new file

                      printf("\n File welcome.txt has been created");

                      getch();

                      return 0;

} 

Output:

 How to close the file:

• The close file is used to close the opened file.

Syntax:

 fclose (file_pointer);

Example:

FILE *fp;

fp  = fopen ("file1.txt", "r");

fclose (fp);

How to writing to a File:

• The write mode is used to write a given content into the file.
• fputc(char, file_pointer): It writes a character to the file pointed to by file pointer.
• fputs(str, file_pointer): It writes a string to the file pointed to by file pointer.
• fprintf(file_pointer, str, variable_lists): It prints a string to the file pointed to by file pointer. The string can optionally include format specifiers and a list of variables variable lists.

Syntax:

pointer_variable =fopen(“file_name.txt”,”w”);

fputc(array_variable, pointer_variable);//if using loop

fputs("text or string", pointer_variable);//without loop

Example program for create the file and write data into the file:

#include <stdio.h>

#include<conio.h>

int main() {

        int i;

        FILE * fptr;//declare pointer variable to file

        char fn[50];

        char str[] = "C file hadling\n";

        fptr = fopen("file1.txt", "w"); // "w" defines "writing mode"

        for (i = 0; str[i] != '\n'; i++) {

            //write to file using fputc() function

            fputc(str[i], fptr);

        }

        fclose(fptr);//close the file

        return 0;

    }

Output:

Example program for w+ mode:

#include <stdio.h>

int main() {

        FILE * fp;

        fp = fopen("FILE1.txt", "w+");

        fputs("w+ is used to read and write operations.", fp);

        fputs("We don't need to use for loop\n", fp);

        fputs("Easier than fputc function\n", fp);

        fclose(fp);

        return (0);

Output:

How to read file:

• Reading file is nothing but, it is used to show on the output screen to know what content inside the file.

Syntax:

 pointer_variable =fopen(“file_name.extention”,”r”);

while( variable_name  != EOF)

  {

    variable_name  = fgetc(pointer_variable);

  }

Example program for read file mode:

#include <stdio.h>

#include<conio.h>

int main()

{

  FILE *fr;

  char c;

  clrscr();

  fr = fopen("f2.c", "r");

  while( c != EOF)

  {

    c = fgetc(fr); // read from file

    printf("%c",c); //display on screen

  }

  getch();

  fclose(fr);

  return 0;

}

Output:

Example program for write and read program:

#include<stdio.h>

#include<conio.h>

int main()

{

   FILE *fp;

   char s[30];

   int n;

   clrscr();

   fp = fopen("output.txt", "w");

   printf("\n Enter a string and a number:\n");

   scanf("%s %d", s, &n); //read from keyboard

   fprintf(fp, "%s %d", s, n); // write to file

   fclose(fp);

   fp = fopen("output.txt", "r");

   printf("\n Read data from output.txt file..... \n");

   fscanf(fr, "%s\n%d", s, &n); //read from file

   printf("%s %d", s, n); //display on screen

  getch();

   fclose(fp);

   return 0;

}

Output:

How to append text into an existing file:

• An append mode is nothing but, it similar to the write mode but it is used to concatenate the text already existing content.
• Write mode is used to write new content into the file.

Syntax:

pointer_variable =fopen(file_name_stored_variable,’a’);

fprintf(fp, "%s\n", content_store_variable);// Write content to file

fclose(fp);//after write the content then close the file

Example:

#include <stdio.h>

#include<conio.h>

int main()

{

   FILE *fp;

   char ch;

   char *filename = "file1.txt";

   char *content = "This text is appended in file1 using C programming.";

   clrscr();

   fp = fopen(filename, "r");//first open and read file for display purpose

   printf("\n Before append text into the file : %s \n", filename);

   while ((ch = fgetc(fp) )!= EOF)

   {

      printf ("%c", ch);

   }

   fclose(fp);//closed after read

   fp = fopen(filename, "a");//again open for append

   fprintf(fp, "%s\n", content);// Write content to file

   fclose(fp);//after write the content then close the file

   fp = fopen(filename, "r");//again file open for read to check 

                                                                                    append or not

   printf("\n After append the text into the file %s \n", filename);

   while ((ch = fgetc(fp) )!= EOF)

   {

      printf ("%c", ch);

   }

   fclose(fp);//closed file

   getch();

   return 0;

}

Output:

Before running the program:

After running the program:

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