C memory management error?

Question

C memory management error?

This is my C program:

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <time.h>
#include <ctype.h>
#define FALSE 0
#define TRUE 1

typedef struct _Frag
{
  struct _Frag *next;
  char *seq;
  int x1;
  int length;
} Frag;

typedef struct _Fragment
{
  int type;
  Frag *frag_list;
} Fragment;

static void
free_frags (Fragment * frags, int len)
{
  int i;
  for (i = 0; i < len; i++)
    {
      Fragment *fragment = &frags[i];
      Frag *current = fragment->frag_list;

      while (current != NULL)
    {
      free (current->seq);
      fragment->frag_list = current->next;
      free (current);
      current = fragment->frag_list;
    }

      /* to do : free fragment */
      free (fragment);
      fragment = NULL;
    }
  free (frags);
}

int
main ()
{
  Fragment *frags = (Fragment *) malloc (10 * sizeof (Fragment));
  int i, j;
  for (i = 0; i < 10; i++)
    {
      Fragment *fragment = &frags[i];
      fragment->frag_list = (Frag *) malloc (1 * sizeof (Frag));
      Frag *frag = fragment->frag_list;
      frag->seq = malloc (6 * sizeof (char));
      strcpy (frag->seq, "55555");
      frag->next = (Frag *) malloc (1 * sizeof (Frag));
      frag = frag->next;
      frag->seq = malloc (6 * sizeof (char));
      strcpy (frag->seq, "55555");
      frag->next=NULL;
    }
  free_frags (frags, 10);
  return 0;
}

when I debug it using gdb, the error message is:

(gdb) run a.out 
..........................
..........................
09574000-09595000 rwxp 00000000 00:00 0          [heap]
b7e00000-b7e21000 rwxp 00000000 00:00 0 
b7e21000-b7f00000 ---p 00000000 00:00 0 
b7f2e000-b7f4b000 r-xp 00000000 08:08 298454     /usr/lib/libgcc_s.so.1
b7f4b000-b7f4c000 rwxp 0001c000 08:08 298454     /usr/lib/libgcc_s.so.1
b7f4c000-b7f4d000 rwxp 00000000 00:00 0 
b7f4d000-b808d000 r-xp 00000000 08:08 67152259   /lib/libc-2.10.1.so
b808d000-b808f000 r-xp 0013f000 08:08 67152259   /lib/libc-2.10.1.so
b808f000-b8090000 rwxp 00141000 08:08 67152259   /lib/libc-2.10.1.so
b8090000-b8094000 rwxp 00000000 00:00 0 
b80ae000-b80af000 r-xp 00000000 00:00 0          [vdso]
b80af000-b80cb000 r-xp 00000000 08:08 67152744   /lib/ld-2.10.1.so
b80cb000-b80cc000 r-xp 0001b000 08:08 67152744   /lib/ld-2.10.1.so
b80cc000-b80cd000 rwxp 0001c000 08:08 67152744   /lib/ld-2.10.1.so
bfc0f000-bfc24000 rw-p 00000000 00:00 0          [stack]

Program received signal SIGABRT, Aborted.
0xb80ae424 in __kernel_vsyscall ()
(gdb) where
#0  0xb80ae424 in __kernel_vsyscall ()
#1  0xb7f77411 in raise () from /lib/libc.so.6
#2  0xb7f78c12 in abort () from /lib/libc.so.6
#3  0xb7fb271d in __libc_message () from /lib/libc.so.6
#4  0xb7fb8581 in malloc_printerr () from /lib/libc.so.6
#5  0xb7fb9c82 in _int_free () from /lib/libc.so.6
#6  0xb7fbcd4d in free () from /lib/libc.so.6
#7  0x08048488 in free_frags (frags=0x9574008, len=10) at main.c:41
#8  0x080485b3 in main () at main.c:65
(gdb)

The valgrind message is as follows:

==2832== Memcheck, a memory error detector.
==2832== Copyright (C) 2002-2008, and GNU GPL'd, by Julian Seward et al.
==2832== Using LibVEX rev 1884, a library for dynamic binary translation.
==2832== Copyright (C) 2004-2008, and GNU GPL'd, by OpenWorks LLP.
==2832== Using valgrind-3.4.1, a dynamic binary instrumentation framework.
==2832== Copyright (C) 2000-2008, and GNU GPL'd, by Julian Seward et al.
==2832== For more details, rerun with: -v
==2832== 
==2832== Invalid read of size 4
==2832==    at 0x8048442: free_frags (main.c:31)
==2832==    by 0x80485B2: main (main.c:66)
==2832==  Address 0x418b034 is 12 bytes inside a block of size 80 free'd
==2832==    at 0x4023EBA: free (in /usr/lib/valgrind/x86-linux/vgpreload_memcheck.so)
==2832==    by 0x8048487: free_frags (main.c:42)
==2832==    by 0x80485B2: main (main.c:66)
==2832== 
==2832== Invalid write of size 4
==2832==    at 0x8048460: free_frags (main.c:36)
==2832==    by 0x80485B2: main (main.c:66)
==2832==  Address 0x418b034 is 12 bytes inside a block of size 80 free'd
==2832==    at 0x4023EBA: free (in /usr/lib/valgrind/x86-linux/vgpreload_memcheck.so)
==2832==    by 0x8048487: free_frags (main.c:42)
==2832==    by 0x80485B2: main (main.c:66)
==2832== 
==2832== Invalid read of size 4
==2832==    at 0x8048471: free_frags (main.c:38)
==2832==    by 0x80485B2: main (main.c:66)
==2832==  Address 0x418b034 is 12 bytes inside a block of size 80 free'd
==2832==    at 0x4023EBA: free (in /usr/lib/valgrind/x86-linux/vgpreload_memcheck.so)
==2832==    by 0x8048487: free_frags (main.c:42)
==2832==    by 0x80485B2: main (main.c:66)
==2832== 
==2832== Invalid free() / delete / delete[]
==2832==    at 0x4023EBA: free (in /usr/lib/valgrind/x86-linux/vgpreload_memcheck.so)
==2832==    by 0x8048487: free_frags (main.c:42)
==2832==    by 0x80485B2: main (main.c:66)
==2832==  Address 0x418b030 is 8 bytes inside a block of size 80 free'd
==2832==    at 0x4023EBA: free (in /usr/lib/valgrind/x86-linux/vgpreload_memcheck.so)
==2832==    by 0x8048487: free_frags (main.c:42)
==2832==    by 0x80485B2: main (main.c:66)
==2832== 
==2832== Invalid free() / delete / delete[]
==2832==    at 0x4023EBA: free (in /usr/lib/valgrind/x86-linux/vgpreload_memcheck.so)
==2832==    by 0x80484A5: free_frags (main.c:45)
==2832==    by 0x80485B2: main (main.c:66)
==2832==  Address 0x418b028 is 0 bytes inside a block of size 80 free'd
==2832==    at 0x4023EBA: free (in /usr/lib/valgrind/x86-linux/vgpreload_memcheck.so)
==2832==    by 0x8048487: free_frags (main.c:42)
==2832==    by 0x80485B2: main (main.c:66)
==2832== 
==2832== ERROR SUMMARY: 55 errors from 5 contexts (suppressed: 13 from 1)
==2832== malloc/free: in use at exit: 0 bytes in 0 blocks.
==2832== malloc/free: 41 allocs, 51 frees, 520 bytes allocated.
==2832== For counts of detected errors, rerun with: -v
==2832== All heap blocks were freed -- no leaks are possible.

Please help me fix them, thanks.

+5

c memory-management free

Charlie epps Sep 03 '09 at 6:32

source share

6 answers

caf · Answer 1 · 2009-09-03T06:52:41+0000

You have a lot of problems.

Here you allocate space for 5 characters, but copy 6 into (the null terminator at the end of the line also needs a space):

  frag->seq = malloc (5 * sizeof (char));
  strcpy (frag->seq, "55555");

At the same time, you never install frag->nextin the second fragone that you highlight. You need to set it to NULL, so that the loop whilein the routine free_fragwill not run in the weeds.

The third problem:

  /* to do : free fragment */
  free (fragment);

fragment, , malloc - 10 , . free(frags) , .

Dipstick · Answer 2 · 2009-09-03T06:44:52+0000

.

Fragment *fragment = &frags[i];
...
...
/* to do : free fragment */
free (fragment);
fragment = NULL;

epatel · Answer 3 · 2009-09-03T06:49:23+0000

, , Bufferoverflow

  frag->seq = malloc (5 * sizeof (char));
  strcpy (frag->seq, "55555");

55555 , 5 .

strdup(),

  frag->seq = strdup("55555");

Daniel Pryden · Answer 4 · 2009-09-03T06:45:01+0000

frag_list Frag, .

:

int
main ()
{
  Fragment *frags = (Fragment *) malloc (10 * sizeof (Fragment));
  int i, j;
  for (i = 0; i < 10; i++)
    {
      Fragment *fragment = &frags[i];
      fragment->frag_list = (Frag *) malloc (1 * sizeof (Frag));
      Frag *frag = fragment->frag_list;
      frag->seq = malloc (5 * sizeof (char));
      strcpy (frag->seq, "55555");
      frag->next = (Frag *) malloc (1 * sizeof (Frag));
      frag = frag->next;
      frag->seq = malloc (5 * sizeof (char));
      strcpy (frag->seq, "55555");
      frag->next = NULL; // <--------------------- This is what you need to do
    }
  free_frags (frags, 10);
  return 0;
}

, malloc() , / , , , . free() , .

Michael Foukarakis · Answer 5 · 2009-09-03T06:43:48+0000

Frag.next ( free_frags()), NULL - .

, - malloc() 5 Frag.seq, , NULL, .

erelender · Answer 6 · 2009-09-03T06:43:49+0000

, . free_frags(), 41, free ();.

C memory management error?

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