Sort directory contents on date modified,

[therealmuffin]

Howdy all,

I'm a beginner in C trying to build my first application. I need to sort the contents of a directory on date modified. I modified a small struct sorting script. However, somewhere it goes wrong as the output is shuffled but not sorted as intended.

In addition I get an Segmentation fault: 11 when writing the file name of one particular file to screen (not the other data or filenames). I hope this has something to do with why it doesn't sort as intended.

Can someone tell me (point me in the right direction) of where it goes wrong?

Thanks in advance, Maarten

Original script:
Sorting Structures : structure sort..«..Structure..«..C Tutorial

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <dirent.h>
#include <time.h>
#include <sys/types.h>
#include <sys/stat.h>


  /* A Quicksort for structures of type address. */
void quick_struct(struct dirent **namelist, int count) {
    qs_struct(namelist,0,count);
}

int qs_struct(struct dirent **namelist, int left, int right) {

    register int i, j;

    struct dirent *temp;
    struct stat ibuf;
    struct stat jbuf;
    struct stat xbuf;
            
    i = left; j = right;

    stat(namelist[i]->d_name, &ibuf);
    stat(namelist[j]->d_name, &jbuf);  
    stat(namelist[(left+right)/2]->d_name, &xbuf);


    do {
        while((ibuf.st_mtime < xbuf.st_mtime) && (i < right)) {
            i++;
            stat(namelist[i]->d_name, &ibuf);
        }
        while((jbuf.st_mtime > xbuf.st_mtime) && (j > left))  {
            j--;
            stat(namelist[j]->d_name, &jbuf);
        }
        if(i <= j) {
            temp = namelist[i];
            namelist[i] = namelist[j];
            namelist[j] = temp;
     
             
            i++; j--;
        }
    
    } while(i <= j);

    if(left < j) qs_struct(namelist, left, j);
    if(i < right) qs_struct(namelist, i, right);


}

int main(void) {
  
    struct dirent **namelist;
    int n;
    const char *targetdirectory = ".";
    
    n = scandir(targetdirectory, &namelist, 0, alphasort);
    
    struct stat buf;
    
    if (n < 0)
        perror("scandir");
    else {
            quick_struct(namelist, n);

        while (n--) {
        
            stat(namelist[n]->d_name, &buf);
            printf("%-23s  %10ld \t %s \n", namelist[n]->d_name, buf.st_mtime, ctime(&buf.st_mtime));
            
            
            free(namelist[n]);
        }
        
        free(namelist);
        
    }
  
  



}

[therealmuffin]

Apparently I forgot to update two structs along the way:

The segmentation fault remains though, but if I can't figure that one out I'll create a new thread.

Kind regards, Maarten

 
    do {
        while((ibuf.st_mtime < xbuf.st_mtime) && (i < right)) {
            i++;
            stat(namelist[i]->d_name, &ibuf);
        }
        while((jbuf.st_mtime > xbuf.st_mtime) && (j > left))  {
            j--;
            stat(namelist[j]->d_name, &jbuf);
        }
        if(i <= j) {
            temp = namelist[i];
            namelist[i] = namelist[j];
            namelist[j] = temp;
      
              
            i++; j--;

            stat(namelist[i]->d_name, &ibuf);
             stat(namelist[j]->d_name, &jbuf);  


        }

[ledow]

I haven't looked at your code in any depth but if those lines segfault, you should inspect the values of: i, j, namelist[i], namelist[j], namelist[i]->d_name, namelist[j]->d_name, ibuf and jbuf immediately prior to them.

I would suggest you do this with a proper debugger, but you can just put each one on a printf on a line of its own before those calls (if you put them all on the same printf, the printf will segfault and it will be hard to tell which part was responsible). My guess is that i and j are out of bounds when you get to that point.

Oh, and "register" means nothing in any vaguely modern compiler.

[Salem]

$ valgrind --db-attach=yes ./a.out 
==2092== Memcheck, a memory error detector
==2092== Copyright (C) 2002-2009, and GNU GPL'd, by Julian Seward et al.
==2092== Using Valgrind-3.6.0.SVN-Debian and LibVEX; rerun with -h for copyright info
==2092== Command: ./a.out
==2092== 
==2092== Syscall param stat(file_name) contains uninitialised byte(s)
==2092==    at 0x4F04DE5: _xstat (xstat.c:38)
==2092==    by 0x400794: qs_struct (bar.c:28)
==2092==    by 0x400716: quick_struct (bar.c:13)
==2092==    by 0x4009C1: main (bar.c:71)
...
(gdb) up
#1  0x0000000000400795 in qs_struct (namelist=0x51b9330, left=0, right=60) at bar.c:28
28	    stat(namelist[j]->d_name, &jbuf);
(gdb) info locals
i = 0
j = 60
temp = 0x4005f0
ibuf = {st_dev = 21, st_ino = 9046210, st_nlink = 13, st_mode = 16877, st_uid = 1000, st_gid = 1000, __pad0 = 0, st_rdev = 0, st_size = 20480, 
  st_blksize = 4096, st_blocks = 40, st_atim = {tv_sec = 1333383593, tv_nsec = 458878153}, st_mtim = {tv_sec = 1333383588, tv_nsec = 748866984}, st_ctim = {
    tv_sec = 1333383588, tv_nsec = 748866984}, __unused = {0, 0, 0}}
jbuf = {st_dev = 85694544, st_ino = 85695408, st_nlink = 85692464, st_mode = 85692752, st_uid = 0, st_gid = 85690544, __pad0 = 0, st_rdev = 0, st_size = 4354, 
  st_blksize = 939536896, st_blocks = 80, st_atim = {tv_sec = 0, tv_nsec = 0}, st_mtim = {tv_sec = 60, tv_nsec = 4354}, st_ctim = {tv_sec = 85688496, 
    tv_nsec = 85693232}, __unused = {0, 4354, 939534736}}
xbuf = {st_dev = 85695120, st_ino = 85695504, st_nlink = 85691824, st_mode = 85689136, st_uid = 0, st_gid = 85691616, __pad0 = 0, st_rdev = 85689856, 
  st_size = 85692656, st_blksize = 85694352, st_blocks = 85691216, st_atim = {tv_sec = 85689344, tv_nsec = 85694032}, st_mtim = {tv_sec = 85694448, 
    tv_nsec = 85692272}, st_ctim = {tv_sec = 85692368, tv_nsec = 85690144}, __unused = {85692560, 85690336, 85689024}}
(gdb) up
#2  0x0000000000400717 in quick_struct (namelist=0x51b9330, count=60) at bar.c:13
13	    qs_struct(namelist,0,count);
(gdb) up
#3  0x00000000004009c2 in main () at bar.c:71
71	            quick_struct(namelist, n);
(gdb) print n
$1 = 60

The first problem is you have j=right, then you try to access namelist[j]
But this is out of bounds (by 1)

[therealmuffin]

Muchas gracias all, as noted my loop was going one round too many.