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"." and ".."

Posted on 2011-03-03
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Last Modified: 2012-05-11
Hi,
 I need explanation of "." and ".." value in d_name of struct direct when reading directory in Linux . Thanks a lot.
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Question by:BeginToLearn
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LVL 143

Expert Comment

by:Guy Hengel [angelIII / a3]
ID: 35034183
"." refers to the current directory itself,
".." refers to the parent directory
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Author Comment

by:BeginToLearn
ID: 35034192
about DT_DIR? could you explan this
 
 if ( DT_DIR & pEntry->d_type && strcmp ( pEntry->d_name, ".") && strcmp ( pEntry->d_name, ".."))

 tks.
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LVL 143

Expert Comment

by:Guy Hengel [angelIII / a3]
ID: 35034206
this condition checks IF the pEntry->d_name value is either "." or ".." , and if the p_entry.d_type is DT_DIR ...
presumable to exclude those from the processing ...
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Author Comment

by:BeginToLearn
ID: 35034216
i now what it check. but i don't understand the meaning of "." and ".." in this case which is reading directory. thanks.
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Author Comment

by:BeginToLearn
ID: 35034222
i mean relate to

"." refers to the current directory itself,
".." refers to the parent directory

can u give example?
tks
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Accepted Solution

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Guy Hengel [angelIII / a3] earned 1800 total points
ID: 35034279
see this "copy/paste" from my dos box:
C:\WINNT>dir
 Volume in drive C is OSDisk
 Volume Serial Number is FC2D-08F6

 Directory of C:\WINNT

03/03/2011  15:44    <DIR>          .
03/03/2011  15:44    <DIR>          ..
03/01/2011  08:17                 0 0.log
10/07/2008  20:58    <DIR>          addins
21/04/2009  13:21    <DIR>          AppPatch
21/01/2008  14:48            12.477 atiogl.xml

Open in new window


so, the "current directory" is the one where you issue the "dir" command from (resp your C function ...)
 Directory of C:\WINNT

Open in new window

the "." refers to that same directly.
and ".." refers to "C:\"  

hope this clarifies
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Author Comment

by:BeginToLearn
ID: 35034319
I understand "." now. It tell where the "dir " command is issued. But why do we need ".."?
any when a program copy a directory ( and its suddirectory ) to another place, do we need to skip "." and ".."? tks.
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LVL 35

Assisted Solution

by:sarabande
sarabande earned 200 total points
ID: 35034415
we don't need the ".." but have to consider it when doing a directory listing and want to use only files or only sub directories.

Sara

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LVL 143

Assisted Solution

by:Guy Hengel [angelIII / a3]
Guy Hengel [angelIII / a3] earned 1800 total points
ID: 35034432
"." and ".." are only logical links, and you cannot "copy" them. they are "created" automatically by the underyling file system.
you just skip them in any processing, the only thing you can do with it is to show them

having ".." means you have a parent folder, if you have no such item in the list, you cannot "go up" one folder.
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Author Comment

by:BeginToLearn
ID: 35034441
tks all. I get it now.
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