CSCI215-Lab 6 File I/O Solved

Question 1: Code analysis
Compile and run the following program:

#define _XOPEN_SOURCE 700

#include <stdio.h

#include <stdlib.h

#include <unistd.h

#include <fcntl.h

#include <string.h

#include <sys/types.h

#include <sys/wait.h

 

int main (void) {

   int fd1, fd2, fd3;

  

   if ((fd1 = open ("./file1", O_RDWR|O_CREAT|O_TRUNC,0600)) == ­1)

       return EXIT_FAILURE;

   if (write (fd1,"abcde", strlen ("abcde")) == ­1) /* A */

       return EXIT_FAILURE;

   if (fork () == 0) {

       if ((fd2 = open ("./file1", O_RDWR)) == ­1)

           return EXIT_FAILURE;

       if (write (fd1,"123", strlen ("123")) == ­1) /* B */

           return EXIT_FAILURE;

       if (write (fd2,"45", strlen ("45")) == ­1) /* C */

           return EXIT_FAILURE;

       close(fd2);

   } else {

       fd3 = dup(fd1);

       if (lseek (fd3,0,SEEK_SET) == ­1) /* D */

           return EXIT_FAILURE;

       if (write (fd3,"fg", strlen ("fg")) == ­1) /* E */

           return EXIT_FAILURE;

       if (write (fd1,"hi", strlen ("hi")) == ­1) /* F */

           return EXIT_FAILURE;

       wait (NULL);

       close (fd1);

       close(fd3);

   }

   return EXIT_SUCCESS;

}

 

Question: what are the possible contents of file file1?

Using signals, modify the program so that the file always contains exactly 8 characters.

 


 

Question 2: Custom file copy
Write a program mycp that takes two filenames as parameters:

$ ./mycp <file1 <file2

This program completely copies the contents of the file file1 into the file file2.

There are 2 conditions required for this program to work without returning an error:

1.  the file file1 must exist and be a regular file,

2.  The file file2 must not exist. 

Question 3: Value sharing via files
Write a program where the initial parent process creates a file, then creates N child processes and waits for their termination. Each child generates a random value random_val, stores it in the file and displays it before exiting. The random value is generated thus:

random_val = (int) (10 * (float) rand () / RAND_MAX);

Once all its children have terminated, the parent process reads all the values in the file, sums them up and then displays the result, and finally deletes the file.

 

Question 4: Extended grep function
 

Write a program extended­grep that searches a directory for files containing a given string.

 

The program will be called as follows:

$ extended­grep <expr <path

with expr the string of characters sought, and path the directory path that contains the files to scan

 

extended­grep reads the contents of all regular files in path, displays the name of each file that contains the search string, or displays "search unsuccessful" if expr is not present in any of the regular files in the directory.

 

N.B: You can use the strstr function of the <string.h library to find if a string is present in another string.