What are various types of files? What are the various modes in which a file can be opened? Explain by giving examples.

The Random Access Memory is volatile and its content is lost once the program terminates. In order to persist the data format forever we use files.

A file is a data data stored in a storage device. A C program can talk to the file by reading content from it and writing content to it.

Types of Files :-

1. Text files (.ext, c)
2. Binary files (.jpg, .dat)

Let's discuss it -

1. Text Files - Text files are regular files that contain information readable by the user. This information is stored in ASCII. You can display and print these files. The lines of a text file must not contain NUL characters, and none can exceed {LINE_MAX} bytes in length, including the new-line character.

1. Binary files - Binary files are regular files that contain information readable by the computer. Binary files may be executable files that instruct the system to accomplish a job. Commands and programs are stored in executable, binary files. Special compiling programs translate ASCII text into binary code.

FILE pointer :- A 'FILE' is a structure which needs to be created for opening the file. A FILE pointer is a pointer to the structure of the file. A FILE pointer is needed for communication between the files and the program.

A FILE pointer can be crated as follows :-

FILE *ptr;
ptr = fopen("filename.txt", "mode");

Files opening modes in C :-

Some of the primarily used opening modes in C are -

1. "r" - Open for reading. If the file does not exist, fopen returns null.
2. "rb" - Open for reading in binary. If the file does not exist, fopen returns null.
3. "w" - Open for writing. If the file exists, the content will be overwritten.
4. "wb" - Open for writing in binary. If the file exists, the content will be overwritten.
5. "a" - Open for append. If the file does not exist, it will be created.

Reading a file : -

A file can be opened for reading as follows :-

FILE *ptr;
ptr = fopen("abc.txt", "r");
int num;

Let us assume that the "abc.txt" contains an integer. We can read that integer using -

fscanf(ptr, "%d", &num);

fscanf is file counterpart of scanf.

This will read an integer form file in num variable.

Closing the file : -

It is very very important to close the file after read or write.

This is achieved using fclose as follows -

fclose(ptr);

This will tell the compiler that we are done working with this file and the associated resource could be freed.

Writing to a file : -

We can write to a file in a very similar manner like we read the file.

FILE *ptr;
fptr = fopen("abc.txt", "w");

int num = 465;
fprintf(fptr, "%d", num);

fclose(fptr);

fgetc() and fputc() : -

fgetc and fputc are used to write and read a character to / from a file.

fgetc(ptr);    //Used to read a character from a file.

fputc('c', ptr);   //Used to write a character 'c' to a file.

EOF : End of the file : -

fgetc returns EOF when all the characters from a file have been read. So we can write a check like below to detect the end of the file.

while(1){
  ch = fgetc(ptr);
  if(ch == EOF){
  break;
  }
  //------
  //Code
  //------
}

When all the content of the file has been read, it will break the loop !

For better understanding, let's take an example.

Suppose, We have to write a program in C to create and store information in a text file.

The code for the same will be -

#include <stdio.h>
#include <stdlib.h>

int main()
{
   char str[1000];
   FILE *fptr;
   char fname[20]="test.txt";

    printf("\n\n Create a file (test.txt) and input text :\n");
    printf("----------------------------------------------\n"); 
   fptr=fopen(fname,"w");   
   if(fptr==NULL)
   {
      printf(" Error in opening file!");
      exit(1);
   }
   printf(" Input a sentence for the file : ");
   fgets(str, sizeof str, stdin);
   fprintf(fptr,"%s",str);
   fclose(fptr);
   printf("\n The file %s created successfully...!!\n\n",fname);
   return 0;
}