How to sort files in some directory by the names on Linux

Question

I use opendir() and readdir() to display the file names in a directory. But they are disordered. How can I sort them? The language is C.

@Christoffer Hammarström: Sorry, I forget to mention I have to use C — JavaMobile, Feb 24 '11 at 10:07
This is harder than it looks because Unix sorts files in idiomatic order, that is, p5A comes before p10A and p50A. Unless you rename files p05A, your alphabetic sort will not get the fine points of sort-by-name. — DragonLord, Aug 19 '17 at 18:11

hipe · Answer 1 · 2011-02-24T15:22:09.673

32

Maybe you could use scandir() instead of opendir and readdir?

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

int
main(void)
{
   struct dirent **namelist;
   int n;

   n = scandir(".", &namelist, 0, alphasort);
   if (n < 0)
       perror("scandir");
   else {
       while (n--) {
       printf("%s\n", namelist[n]->d_name);
       free(namelist[n]);
       }
       free(namelist);
   }
}

edited Feb 24 '11 at 15:22

answered Feb 24 '11 at 10:41

hipe

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8

In fact, I try to use it, but it has some errors. Could you give some examples or details? – JavaMobile Feb 24 '11 at 13:12
3

You can find an example for how to use `scandir` (with alphabetic sorting) in the specification (see the examples section): http://pubs.opengroup.org/onlinepubs/9699919799/functions/scandir.html – R.. GitHub STOP HELPING ICE Feb 24 '11 at 15:10

score 8 · Accepted Answer · answered Feb 24 '11 at 12:37

8

The idiomatic way to sort something in C is to use the qsort() function. For this to work, it's best if you can arrange to have all the file names collected into an array of pointers, and then you sort the array.

This is not too hard, but it does require either a bit of dynamic-array management, or that you introduce static limits on things (maximum length of filenames, maximum number of files).

answered Feb 24 '11 at 12:37

unwind

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2

`scandir` does this for you. The only bad part about it is that you can't specify the directory using a file descriptor; you have to pass the name. – R.. GitHub STOP HELPING ICE Feb 24 '11 at 15:14

score 0 · Answer 3 · answered Feb 24 '11 at 14:39

You have to dynamically construct a data structure containing the filenames and make sure it is sorted.

You could build an array or linked list with the names, and then sort that, but my preference is to sort the values on insertion by inserting into a binary tree.

How to sort files in some directory by the names on Linux

3 Answers3

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