C program to read a range of bytes from file and print it to console

Given a file F, the task is to write C program to print any range of bytes from the given file and print it to a console.

Functions Used:

1. fopen(): Creation of a new file. The file is opened with attributes as “a” or “a+” or “w” or “w++”.
2. fgetc(): Reading the characters from the file.
3. fclose(): For closing a file.

Approach:

• Initialize a file pointer, say File *fptr1.
• Initialize an array to store the bytes that will be read from the file.
• Open the file using the function fopen() as fptr1 = fopen(argv[1], “r”).
• Iterate a loop until the given file is read and stored, the characters are scanned in the variable, say C using the fgetc() function.
• Store each character C extracted in the above step, to a new string S and print that string using the printf() function.
• After completing the above steps, close the file using the fclose() function.

Below is the implementation of the above approach:

C

// C program to read particular bytes
// from the existing file
#include <stdio.h>
#include <stdlib.h>

// Maximum range of bytes
#define MAX 1000

// Filename given as the command
// line argument
int main(int argc, char* argv[])
{
    // Pointer to the file to be
    // read from
    FILE* fptr1;
    char c;

    // Stores the bytes to read
    char str[MAX];
    int i = 0, j, from, to;

    // If the file exists and has
    // read permission
    fptr1 = fopen(argv[1], "r");

    if (fptr1 == NULL) {
        return 1;
    }

    // Input from the user range of
    // bytes inclusive of from and to
    printf("Read bytes from: ");
    scanf("%d", &from);
    printf("Read bytes upto: ");
    scanf("%d", &to);

    // Loop to read required byte
    // of file
    for (i = 0, j = 0; i <= to
                       && c != EOF;
         i++) {

        // Skip the bytes not required
        if (i >= from) {
            str[j] = c;
            j++;
        }

        // Get the characters
        c = fgetc(fptr1);
    }

    // Print the bytes as string
    printf("%s", str);

    // Close the file
    fclose(fptr1);

    return 0;
}

Output: