How to get file information similar to "ls -la" using C?

Question

I am using ar.h for the defining the struct. I was wondering on how I would go about getting information about a file and putting it into those specified variables in the struct.

struct ar_hdr {
    char ar_name[16];       /* name of this member */
    char ar_date[12];       /* file mtime */
    char ar_uid[6];         /* owner uid; printed as decimal */
    char ar_gid[6];          /* owner gid; printed as decimal */
    char ar_mode[8];        /* file mode, printed as octal   */
    char ar_size[10];       /* file size, printed as decimal */
    char ar_fmag[2];        /* should contain ARFMAG */
};

Using the struct defined above, how would I put get the information from the file from ls -la

-rw-rw----. 1 clean-unix upg40883 368 Oct 29 15:17 testar

?

You can get the output of ls as explained here http://stackoverflow.com/questions/646241/c-run-a-system-command-and-get-output then parse it and populate your structure. — lc2817, Oct 30 '11 at 03:57
See also http://stackoverflow.com/questions/857156/how-to-implement-unix-ls-l-command-in-c — John Carter, Oct 30 '11 at 04:14

score 10 · Accepted Answer · answered Oct 30 '11 at 03:58

10

You're looking for stat(2,3p).

answered Oct 30 '11 at 03:58

Ignacio Vazquez-Abrams

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You're right it is a more proper way to do it than what I suggested. – lc2817 Oct 30 '11 at 04:00
That looks like it. What if I have multiple files.. for instance I run this command. `% ./foo file1 file2 file3`. Is it possible to get all three of those files information? Trying to program the `ar -q` command in unix. lol – inoobdotcom Oct 30 '11 at 04:39
Yay, it worked. Thanks so much. I used fstat too. Now I just need to loop it so it can display more than just one file at a time. Awesome. By any chance would you know how to put it into a archive file using the struct? Anyways, you have been very helpful. – inoobdotcom Oct 30 '11 at 04:51

score 1 · Answer 2 · answered Oct 30 '11 at 04:36

In order to emulate the behavior of ls -la you need a combination of readdir and stat. Do a man 3 readdir and a man 2 stat to get information on how to use them.

Capturing the output of ls -la is possible, but not such a good idea. People might expect that of a shell script, but not a C or C++ program. It's even sort of the wrong thing to do in Python or perl if you can help it.

You will have to construct your structure yourself from the data available to you. strftime can be used for formatting the time in a manner you like.

score 0 · Answer 3 · answered Oct 30 '11 at 04:40

For collecting data about a single file into an archive header entry, the primary answer is stat(); in other contexts (such as ls -la), you might also need to use lstat() and readlink(). (Beware: readlink() does not null terminate its return string!)

With ls -la, you would probably use the opendir() family of functions (readdir() and closedir() too) to read the contents of a directory.

If you needed to handle a recursive search, then you'd be looking at nftw(). (There's also a less capable ftw(), but you'd probably be better off using nftw().)

How to get file information similar to "ls -la" using C?

3 Answers3

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