C++ Dirent.h - File traversal algorithm

[Sub101]

Hi all,

Im currently creating an algorithm for directory traversal. The algorithm runs a method if a file is found and moves into the directory if a directory is found.

  
if(entry->type == DT_DIR){
//Run method inside this directory
}
if(entry->type == DT_REG){
// Do stuff on the file
}

The problem, however, is that in some cases the entry->type is thought to be a file when it is a Directory. Has anyone come across this before, and does anyone have any solutions?

Thanks for your time.

[Arndt]

Hi all,

Im currently creating an algorithm for directory traversal. The algorithm runs a method if a file is found and moves into the directory if a directory is found.

  
if(entry->type == DT_DIR){
//Run method inside this directory
}
if(entry->type == DT_REG){
// Do stuff on the file
}

The problem, however, is that in some cases the entry->type is thought to be a file when it is a Directory. Has anyone come across this before, and does anyone have any solutions?

Thanks for your time.

I think more details are needed. Why not the whole program, reduced so that it still shows the error?

[gmargo]

Oops. More details needed. Could you be changing the type?

[FoxEWolf]

Oops. More details needed.

Seconded!

[t1497f35]

I strongly suggest you stop using dirent.d_type for checking the type of the file.
I just made this mistake in my app and had to rewrite it to use stat instead.
That's because i.e. on XFS dirent.d_type is not supported because dirent only guarantees that the filename (d_name) always be present.

char d_name[]
This is the null-terminated file name component. This is the only field you can count on in all POSIX systems.

Source:
http://www.gnu.org/s/libc/manual/htm...ectory-Entries

Researching this I found bugs on launchpad about apps because they've been relying on dirent.d_type and the solution was to switch over to stat.

PS: since you're using dirent/stat (and if file size etc matters to your algorithm) don't forget about the LFS issue, which in glib's gio and other higher level APIs is taken care of automatically.

[johnl]

I strongly suggest you stop using dirent.d_type for checking the type of the file.
I just made this mistake in my app and had to rewrite it to use stat instead.
That's because i.e. on XFS dirent.d_type is not supported because dirent only guarantees that the filename (d_name) always be present.

Source:
http://www.gnu.org/s/libc/manual/htm...ectory-Entries

Researching this I found bugs on launchpad about apps because they've been relying on dirent.d_type and the solution was to switch over to stat.

I think this is good advice, use dirent to determine the filename, and then do a stat or lstat on the file. Something like this (in C, in C++ you could use a std::stringstream or std::string instead of namebuf/snprintf/etc):

#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <dirent.h>
#include <unistd.h>
#include <string.h>
#include <limits.h>

static void list_dir(const char* base_dir) 
{
    DIR* dir;
    struct dirent* ent;
    struct stat buf;
    
    char namebuf[PATH_MAX];
    size_t base_len = strlen(base_dir);
    
    if (!(dir = opendir(base_dir))) {
        perror("failed to open directory");
        return;
    }
    
    while((ent = readdir(dir)) != NULL) {
        /* ignore .. and . */
        if (!strcmp(ent->d_name, "..") || !strcmp(ent->d_name, ".")) {
            continue;
        }
        
        snprintf(namebuf, sizeof(namebuf), "%s%s%s",
                 base_dir,
                 (base_dir[base_len - 1] == '/' ? "" : "/"),
                 ent->d_name);

        if (lstat(namebuf, &buf) != 0) {
            perror(namebuf);
            continue;
        }

        if (S_ISREG(buf.st_mode)) {
            printf("FILE: %s\n", namebuf);
        } else if (S_ISLNK(buf.st_mode)) {
            printf("LINK: %s\n", namebuf);
        } else if (S_ISDIR(buf.st_mode)) {
            printf("DIR:  %s\n", namebuf);
            /* recurse, if desired */
            /* list_dir(namebuf);  */
        }
    }

    closedir(dir);
}

[Sub101]

Thanks for your help all. Ill use stat as suggested.