readdir and dynamic array memory corruption Post: 302491516

Sponsored Content

Top Forums Programming readdir and dynamic array memory corruption Post 302491516 by torbium on Thursday 27th of January 2011 04:34:26 PM

01-27-2011

Registered User

readdir and dynamic array memory corruption

Hi everyone

I am developing an utility.
At some part of it I read directory entries to a dynamic array: struct list
It stores pointers to items: list.entries,
which are structures: struct entry

If a number of files in a directory is greater then number of elements an array was initially allocated,
I reallocate memory for this array.
if (c > list_size)

And at this point something strange happens.
Pointers are correct.
While I can successfully allocate memory for new items
list.entries[c] = malloc(sizeof(struct entry));
list.entries[0]->pde->d_name is corrupted at some iteration, but always if list.entries was reallocated.

See the test code provided.

If I do not realloc list.entries everything goes fine.
I played with list_size values.
On Mac OS X (10.4.0 Darwin Kernel Version 10.4.0) memory is corrupted while list.entries[124] is processed.
On Ubuntu Linux 2.6.24-23-xen #1 SMP Wed Apr 1 23:47:10 UTC 2009 x86_64 GNU/Linux while list.entries[196] is processed.
If I don't use readdir and explicitly allocate
list.entries[c]->pde = malloc(sizeof(struct dirent));
memory is not corrupted.

What is wrong?
Where is the problem?
What is the best way to read dir entries to a dynamic array?

Code:

#include <sys/stat.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <dirent.h>
#include <math.h>
#include <pwd.h>
#include <dirent.h>
#include <unistd.h>

int
main (void)
{
    int i, c, ac;
    unsigned int list_size = 10;
    char * fname;
    
    DIR *pdir;
    struct dirent *pde;
    
    
    struct entry {
        struct stat st;
        struct dirent *pde;
    };
    
    struct list {
        int count;
        struct entry **entries;
    } list;
    
    struct entry **ppent;
    pdir = NULL;
    pde = NULL;
    
    pdir = opendir("/usr/bin");
    
    if ((list.entries = malloc(list_size * sizeof(struct entry *))) == NULL)
        return 1;
    
    c = 0;
    ac = 0; /* allocation counter */
    while ((pde = readdir(pdir)) != NULL) {
        if (c > list_size - 1) {
            list_size <<= 1;
            if ((list.entries = realloc(list.entries,
                                    list_size * sizeof(struct entry*))) == NULL) {
                perror("unable to realloc");
                return 1;
            }
            ac++;
        }

        list.entries[c] = malloc(sizeof(struct entry));
        list.entries[c]->pde = pde;

        if (strcmp(list.entries[0]->pde->d_name, ".") != 0) {
            printf("memory corruption. size of array %d items\n", c);
            printf("number of reallocations %d\n", ac);
            return 1;
        }
        
        printf("base address: %p pointer address: %p entry pointer value: %p name: %s\n",
               list.entries, &list.entries[c], list.entries[c], list.entries[c]->pde->d_name);
        c++;
    }
    
    return 0;
}

torbium

View Public Profile for torbium

Find all posts by torbium

10 More Discussions You Might Find Interesting

1. Programming

Creating an array to hold posix thread ids: Only dynamic array works

I am facing a strange error while creating posix threads: Given below are two snippets of code, the first one works whereas the second one gives a garbage value in the output. Snippet 1 This works: -------------- int *threadids; threadids = (int *) malloc (num_threads * sizeof(int)); ...

2. UNIX for Dummies Questions & Answers

'memory corruption' error when using Awk

Hello, everyone. I got the following error when I am using awk to analysis some text file: *** glibc detected *** awk: malloc(): memory corruption: 0x080c67f8 *** ======= Backtrace: ========= /lib/tls/i686/cmov/libc.so.6 /lib/tls/i686/cmov/libc.so.6...

3. Programming

Why does this occur? * glibc detected * malloc(): memory corruption: 0x10013ff8 ***

there seems not to be error in this segment. In some computers, it can work well. But in others, it will give a failure. why it ocurrs and how to deal with it? in a function: if( *ver == NULL ) { *ver = (vertex *) malloc(sizeof(vertex)); //this line ...

4. SCO

SCO openserver Dynamic linker corruption

Hi every body I have a problem like that "Dynamic linker error" message. I can't load many of programs in sco unix openserver 5.0.6. I guess this problem appear after my last effort to install "SCO Development System" package. How can I fix this problem? would you please help me ?

5. Programming

./match_pattern.out: malloc(): memory corruption: 0x0000000013a11600 ***

Hi All, I have a simple code which does some computation by matching string patterns. In brief: 1. The code reads .dat and .txt files. 2. .dat files are huge text files and .txt files contain some important words. 3. I am just doing strstr to find the patterns. 4. The function returns the...

6. Programming

* glibc detected * ./a.out: malloc(): memory corruption (fast):

*** glibc detected *** ./a.out: malloc(): memory corruption (fast): Posted A minute ago M trying to make multiway tree and dont know what happend when this part of code get executed: 01void ins(NODE *ptr) 02{ 03 //working 04 if(ptr!=NULL) 05 { 06 SNODE *var=NULL; 07 var=(SNODE...

7. Programming

* glibc detected * : malloc(): memory corruption (fast)

Hi Friends, while executing the below code, am getting *** glibc detected *** ./ok: malloc(): memory corruption (fast) error, please suggest how to solve this issue. #include <stdio.h> #include <string.h> #include <sqlca.h> #include <alloca.h> /* Define constants for VARCHAR...

8. Programming

* glibc detected * ./a.out malloc() memory corruption

I am facing a problem of memory corruption. The loop runs for the first time but does not go through the second time. What could be the problem? for(int z=0;z<2;z++) { fp=fopen("poly.dat","r"); /*do something which reads this file into a 2D array*/ fclose(fp); ...

9. Solaris

Solaris 10 Shared Memory Corruption with X11

I am having a problem with shared memory corruption. I have two 86 servers running Solaris 10 (150400-06). One of the servers is accessed by a Sun Ray thin client Version 11.1.3.0.2.6. I login into server one from the thin client. I then ssh -X to server two. When a process that contains a...

10. Programming

Memory corruption in dynamic array of strings

I put together a C function to add strings to a dynamic array of strings (mostly for educational purpose to explain pointers to my kid). It works, but sometimes one or two strings in the array becomes corrupted. Running example on 64 bit Ubuntu, gcc ver. 4.8.4 Hope my code is self-explanatory: ...

LEARN ABOUT MOJAVE

scandir

SCANDIR(3)						   BSD Library Functions Manual 						SCANDIR(3)

NAME

     scandir, scandir_b, alphasort -- scan a directory

SYNOPSIS

     #include <sys/types.h>
     #include <dirent.h>

     int
     scandir(const char *dirname, struct dirent ***namelist, int (*select)(const struct dirent *),
	 int (*compar)(const struct dirent **, const struct dirent **));

     int
     alphasort(const struct dirent **d1, const struct dirent **d2);

     int
     scandir_b(const char *dirname, struct dirent ***namelist, int (^select)(const struct dirent *),
	 int (^compar)(const struct dirent **, const struct dirent **));

DESCRIPTION

     The scandir() function reads the directory dirname and builds an array of pointers to directory entries using malloc(3).  It returns the num-
     ber of entries in the array.  A pointer to the array of directory entries is stored in the location referenced by namelist (even if the num-
     ber of entries is 0).

     The select argument is a pointer to a user supplied subroutine which is called by scandir() to select which entries are to be included in the
     array.  The select routine is passed a pointer to a directory entry and should return a non-zero value if the directory entry is to be
     included in the array.  If select is null, then all the directory entries will be included.

     The compar argument is a pointer to a user supplied subroutine which is passed to qsort(3) to sort the completed array.  If this pointer is
     null, the array is not sorted.

     The alphasort() function is a routine which can be used for the compar argument to sort the array alphabetically.

     The memory allocated for the array can be deallocated with free(3), by freeing each pointer in the array and then the array itself.

     The scandir_b() function works the same way as the scandir() function, except that select and compar are blocks instead of subroutines.

DIAGNOSTICS

     Returns -1 if the directory cannot be opened for reading or if malloc(3) cannot allocate enough memory to hold all the data structures.

SEE ALSO

     directory(3), malloc(3), qsort(3), dir(5)

HISTORY

     The scandir() and alphasort() functions appeared in 4.2BSD.  The scandir_b() function appeared in Mac OS X 10.6.

BSD
								   May 20, 2008 							       BSD

10 More Discussions You Might Find Interesting

1. Programming

Creating an array to hold posix thread ids: Only dynamic array works

Discussion started by: kmehta

2. UNIX for Dummies Questions & Answers

'memory corruption' error when using Awk

Discussion started by: kooyee

3. Programming

Why does this occur? * glibc detected * malloc(): memory corruption: 0x10013ff8 ***

Discussion started by: cdbug

4. SCO

SCO openserver Dynamic linker corruption

Discussion started by: javad1_maroofi