readdir() beginning with dots instead of files

Question

I have a little problem. I'm reading files from directory and it works, but it read two extra files on the beginning ...what is it? for example, there is a list of files: "A348", "A348A", "A348B" and this is what i get: ".", "..", "A348", "A348A", "A348B" ???

DIR *dir;
struct dirent *dp;
char * file_name;
while ((dp=readdir(dir)) != NULL) {

        file_name = dp->d_name;            
}

Ok, I though that, but I want to get only file names... Any ideas how to do it? — user3036674, Nov 28 '13 at 11:48

score 27 · Answer 1 · edited Jul 31 '17 at 12:57

27

. is a directory entry for current directory

.. is a directory entry for the directory one level up in hierarchy

You have to just filter them out using:

if ( !strcmp(dp->d_name, ".") || !strcmp(dp->d_name, "..") )
{
     // do nothing (straight logic)
} else {
     file_name = dp->d_name; // use it
}

More on using . and .. on Windows:

".\\file" - this is a file named file in current working directory

"..\\file" - this is a file in a parent directory

"..\\otherdir\\file" - this is a file that is in directory named otherdir, that is at the same level as current directory (we don't have to know what directory are we in).

Edit: selfcontained example usage of readdir:

#include <stdio.h>
#include <dirent.h>
#include <string.h>

int main()
{
    DIR *dir;
    struct dirent *dp;
    char * file_name;
    dir = opendir(".");
    while ((dp=readdir(dir)) != NULL) {
        printf("debug: %s\n", dp->d_name);
        if ( !strcmp(dp->d_name, ".") || !strcmp(dp->d_name, "..") )
        {
            // do nothing (straight logic)
        } else {
            file_name = dp->d_name; // use it
            printf("file_name: \"%s\"\n",file_name);
        }
    }
    closedir(dir);
    return 0;
}

edited Jul 31 '17 at 12:57

Community

1
1

answered Nov 28 '13 at 11:47

nio

5,141
2
24
35

The are not only aliases. On e.g. UNIX systems they are actual directory entries in the file system, stored on disk even. – Some programmer dude Nov 28 '13 at 11:48
1

@nio: It doesn't work.... but never mind I've already fix it...Don't ask me why but I add dp=readdir(dir); dp=readdir(dir); before while() and it works... – user3036674 Nov 28 '13 at 11:52
1

@user3036674 That is a really bad idea. nio's code is how to do it properly, if it doesn't work chances are you made some mistake. – unwind Nov 28 '13 at 11:57
3

@user3036674 That's an awful idea. No standard guarantees that '.' and '..' come first from `readdir`. They usually do, but sometimes they won't and your program will break in a mysterious way. Do it properly. – Art Nov 28 '13 at 12:00
Ok guys I try nio's idea again.. I know that what I did is dirty as hell... :D thanks for help :) – user3036674 Nov 28 '13 at 12:13
@Art Example: A top level directory may not a "..". – chux - Reinstate Monica Nov 28 '13 at 15:44
10

@chux Actually, they usually do. I'll admit to a dirty secret here. I've implemented filesystems in the past. Our `readdir` didn't return '.' and '..' as the first two entries and so many applications broke it wasn't even funny. We then decided to just internally special case things in the kernel and return '.' and '..' as the first two entries because the effort of bug reporting every broken application was too much (they essentially did that readdir twice trick). I suspect this is also why root directories fake having a '..', because there is too much broken code out there. – Art Nov 28 '13 at 16:16

score 0 · Answer 2 · answered Nov 28 '13 at 11:50

0

Avoid taking the files whose name . and ..

answered Nov 28 '13 at 11:50

Srikanth

447
2
8

readdir() beginning with dots instead of files

2 Answers2

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