Question

Write a C program called last10 that prints the last ten lines of a text file. The program can be used from the command line with:

last10 filename or

last10

If there is no filename, last10 processes standard input.

Answer 1

Here is the solution for above problem

1) In the solution below I am trying to first calculate the total number of lines in a file, after that I am reading the same file again till the last ten line. At the last ten lines I will use the previously calculated number of Lines to print the last ten lines . I have provided the necessary comments in the program below to understand it

C Code

#include<stdio.h>
#include<stdlib.h>
int main(int argc , char **argv)
{

    char *filename=(char *) malloc(sizeof(char) * 1000);
    // reading the input argument filename
    if(argc>1) {
        filename = argv[1];
    }
    else {
        //if input argument is not present taking the file name input from the console
        printf("Enter the file Name: ");
        scanf("%s", filename);
    }
    //for storing a single line from the file
    char *line= (char *) malloc(sizeof(char)*1000);
    int noOfLines=0;//calculating the number of lines in the file
    size_t length=0;// size of each line
    ssize_t read;
    FILE *ptr; // file pointer
    int count=0;
    //trying to open a file
    if((ptr= fopen(filename,"r"))==NULL)
    {
        printf("Cannot open the file");
    }
    //reading the file line by line and calculating the number of lines in the line
    while((read=getline(&line,&length,ptr))!=-1)
    {
        noOfLines++;
    }
// closing the file
    fclose(ptr);
    //trying to open the file
    if((ptr= fopen(filename,"r"))==NULL)
    {
        printf("Cannot open the file");
    }
    //reading the file line by line
    while((read=getline(&line,&length,ptr))!=-1)
    {
        if(count>=(noOfLines-10)) // this count variable is used to check if we are at the last 10 lines
            printf("%s\n",line);
        count++;
    }
   //closing the file again
    fclose(ptr);

    return 0;
}

INPUT FILE (It is from the sherlock holmes novel)

OUTPUT OF CODE

Screenshot of code