Concepts:
System calls opendir, readdir, stat, structure struct stat and structure struct dirent to manage with files and directories

Text:
Realize a program that reads the content of a direcoty and prints some information regarding the files contained in it. The name of the directory is the only parameter of the program.

The program must print:

• for any file contained in the directory: the name of the file and its dimension in bytes with the following format
  FILE: <file_name> <file_dimension_in_bytes>

• for any subdirectory: the name of the subdirectory with the following format
  DIR: <directory_name>

The two special directories “.” (current directory) and “..”

(parent directory) should not be analyzed.

Example:
The program applied to a directory with name dir that contains three subdirectories (dir1, dir2, and dir3) and two files (file1 and file2) with dimensions of 50 and 6 bytes respectively, must provide the following output:

$ ./directory dir
DIR: dir/dir2
DIR: dir/dir1
DIR: dir/dir3
FILE: dir/file2 6
FILE: dir/file1 50

Solution:

directories.c

#include  <sys/types.h> /* for opendir, stat */
#include  <dirent.h>    /* for opendir */
 
#include  <sys/stat.h>  /* for stat */
#include  <unistd.h>    /* for stat */
 
#include  <stdio.h>
#include  <stdlib.h>
#include  <string.h>
 
 
#define N 100
 
 
int main (int argc, char *argv[]) {
  DIR *dp;
  struct stat statbuf;
  struct dirent *dirp;
  char name[N], *dirName;
 
  if (argc != 2) {
    fprintf(stderr, "Usage: %s <pathname>\n", argv[0]);
    exit(EXIT_FAILURE);
  }
 
  /* Open the directory */
  dirName = argv[1];
  if ( (dp = opendir(dirName)) == NULL) {
    fprintf(stderr, "Error on opening directory: %s\n", argv[1]);
    exit(EXIT_FAILURE);
  }
 
  /* Cycle on the elements contained in the directory */
  while ( (dirp = readdir(dp)) != NULL) {
    /* generate the path of an element contained in the directory */
    sprintf (name, "%s/%s", dirName, dirp->d_name);
 
    /* Check if the element is a special directory (i.e., "." or "..") */
    if (strcmp(dirp->d_name, ".") != 0 && strcmp(dirp->d_name, "..") != 0) {
 
      /* Analyze the element */
      if (stat(name, &statbuf) < 0 ) {
        fprintf (stderr, "Error executing system call stat\n");
        exit (EXIT_FAILURE);
      }
 
      if (S_ISDIR(statbuf.st_mode)) {
        /* If it is a directory */
        printf("DIR: %s\n", name);
      } else if (S_ISREG(statbuf.st_mode)) {
        /* If it is a file */
        printf("FILE: %s %ld\n", name, (long)statbuf.st_size);
      }
 
    }
  }  
 
  /* Chiusura della directory */
  if (closedir(dp) < 0) {
    fprintf (stderr, "Close the directory\n");
    exit (EXIT_FAILURE);
  }
 
  return (EXIT_SUCCESS);
}