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 (http://www.gnu.org/s/libc/manual/html_node/Reading-Attributes.html#Reading-Attributes) 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/html_node/Directory-Entries.html#Directory-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 (http://en.wikipedia.org/wiki/Large_file_support) 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 (http://www.gnu.org/s/libc/manual/html_node/Reading-Attributes.html#Reading-Attributes) 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/html_node/Directory-Entries.html#Directory-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.