Question

****NOTE YOU MUST USE SYSTEM CALL I/O, meaning STANDARD I/O IS NOT ALLOWED THIS MEANS THAT YOU CANT USE fopen, fclose , etc

*******You are ONLY ALLOWED TO USE SYSTEM CALL I/O such as read, write, open and close (System I/O functions)

Write a C program using system call I/O to determine how many lines there are in a text file.

Answer 1

Here, we are using system calls I/O to determine the total number of lines in a text file.

Steps to be followed:

• First of all check the value of file descriptor(fd), if the value is -1 then it means there is some problem with the file. In general, in our case, the value of "fd" will be 3, it means we are good to go.
• Now, read the file and store it in a character array.
• Initialize a lineCounter variable to 0.
• Now traverse the array from the beginning and increase the lineCounter if we get any new line ('\n')
• Finally, print the value of lineCounter when the full traversal is complete.

Please refer to the comments of the program for more clarity.

#include<unistd.h>
#include<stdio.h>
#include<fcntl.h>

int main()
{
    int fd,i;  // Initialized the variables which we will be using throughout the program
    fd = open("calls.txt", O_RDWR); // Opening the file
    int lineCount = 0;   // Initialized the lineCount or the lineCounter to 0
    char msg[1000];  // Initialized the char array to store the contents of the text file
    /*
     When fd == -1, it means file is invalid and in our cases the value of fd will be 3 since the value 1 and 2 is already reserved..
    */
    if(fd != -1)
    {
        read(fd, msg, sizeof(msg));  // Reading the file
        for(i=0;i<sizeof(msg);i++)
        {
            if(msg[i]=='\n')   // Checking the new line in the file.
                lineCount++;   // Increasing the counter if we find any new line
        }

        printf("Total number of lines: %d",lineCount);  // Finally, printing the lineCount.
    }
    return ;
}

Sample Input-Output/Code-run:

Random file:

Output:

Note:

Please choose the file which you will be reading in the program carefully. I mean please make sure that the text file is not having any unwanted new lines, line spaces.

Please let me know in the comments in case of any confusion. Also, please upvote if you like.