Question

I am trying the listing directories example from K&R section 8.6, but when testing the code it, says “can’t access” for every single file in the directory. It is because it’s designed for Unix? Below is what I think the code should look like when pieced together, what am I missing? ADD:How do I fix this code to make it work?

#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include "dirent.h"
#include <sys/dir.h>
#define NAME_MAX 14

typedef struct {
  long ino;
  char name[NAME_MAX+1];
} Dirent;

void fsize(char *);

/* print file sizes */
main(int argc, char **argv)
{
  if (argc == 1)
    fsize(".");
  else
    while (--argc > 0)
      fsize(*++argv);
  return 0;
}

void dirwalk(char *, void (*fcn)(char *));

/* fsize: print size of file "name" */
void fsize(char *name)
{
  struct stat stbuf;

  if (stat(name, &stbuf) == -1) {
    fprintf(stderr, "fsize: can't access %s\n", name);
    return;
  }
  if ((stbuf.st_mode & S_IFMT) == S_IFDIR)
    dirwalk(name, fsize);
  printf("%81d %s\n", stbuf.st_size, name);
}

#define MAX_PATH 1024

/* dirwalk: apply fn to all files in dir */
void dirwalk(char *dir, void (*fcn)(char *))
{
  char name[MAX_PATH];
  Dirent *dp;
  DIR *dfd;

  if ((dfd = opendir(dir)) == NULL) {
    fprintf(stderr, "dirwalk: can't open %s\n", dir);
    return;
  }

  while ((dp = readdir(dfd)) != NULL) {
    if (strcmp(dp->name, ".") == 0
    || strcmp(dp->name, "..") == 0)
      continue;
    if (strlen(dir)+strlen(dp->name)+2 > sizeof(name))
      fprintf(stderr, "dirwalk: name %s/%s too long\n",
          dir, dp->name);
    else {
      sprintf(name, "%s/%s", dir, dp->name);
      (*fcn)(name);
    }
  }
  closedir(dfd);
}

Answer 1

The structure Dirent defined in your example probably doesn’t match struct dirent for your system (it doesn’t on mine).

On a Linux system the following will fix the problem:

/* dirwalk: apply fn to all files in dir */
void dirwalk(char *dir, void (*fcn)(char *))
{
    char name[MAX_PATH];
    struct dirent *dp;

    DIR *dfd;

    if ((dfd = opendir(dir)) == NULL) {
            fprintf(stderr, "dirwalk: can't open %s\n", dir);
            return;
    }

    while ((dp = readdir(dfd)) != NULL) {
            if (strcmp(dp->d_name, ".") == 0
                            || strcmp(dp->d_name, "..") == 0)
                    continue;
            if (strlen(dir)+strlen(dp->d_name)+2 > sizeof(name))
                    fprintf(stderr, "dirwalk: name %s/%s too long\n",
                                    dir, dp->d_name);
            else {
                    sprintf(name, "%s/%s", dir, dp->d_name);
                    (*fcn)(name);
            }
    }
    closedir(dfd);
}

The readdir function is system-specific, so you should consult the documentation for yours. On a Linux system you can type man 2 readdir in a terminal to see the online manual for the readdir function.