Very Computer

1. Tricky bug in program caused by delete/delete [] - help

Hello fellow linux developers. I seem to be having some serious problems
with the dynamic memory allocation routines in C++. I am using a pretty
vanilla Slackware 2.0.0- libc 4.5.26, gcc 2.5.8, kernel 1.1.54/62.

What I am trying to do is create a dynamically sized list of char
pointers. When adding one, the old char ** array is reallocated and
the old contents are copied into it. The routine that accomplishes
this is add_stringlist(), below. Another routine involved is clear(),
also below, which deallocates the list once and for all. However,
when the "delete" statement is called, the program crashes with a
segmentation fault. Not on the first time, mind you- it takes a few tries
before it happens- but generally less than ten. I've tried both
"delete" and "delete []." (The function newdup does a strdup but
allocates the memory with new.)

I am completely stumped. Would anyone have any help for me? This was
happening yesterday with another deallocation of a char ** that I was
trying to do as well- I eventually just stopped deallocating it due to
frustration.

A trace from GDB follows, as well as the two code fragments. I appreciate
all responses.

Cheers,

Doug

A trace from GDB 4.12 reveals:

(gdb) where
#0  0x14521 in _free_internal (ptr=0x2000) at free.c:169
#1  0x14602 in free (ptr=0x2000) at free.c:217
#2  0xfe30 in __builtin_delete (ptr=0x2000)

    toadd=0x2c300 "somestring") at somefile.C:103
...
(gdb) list
98        int i;
99      
100       newlist = new char *[count + 1];
101       for (i = 0; i < count; i++)
102         newlist[i] = list[i];
103       delete [] list;
104       list = newlist;
105       list[count++] = newdup(toadd);
106     }
107    

void add_stringlist(int &count, char ** &list, const char *toadd)
{
  char **newlist;
  int i;

  newlist = new char *[count + 1];
  for (i = 0; i < count; i++)
    newlist[i] = list[i];
  delete [] list;
  list = newlist;
  list[count++] = newdup(toadd);

void some_class::clear(void)
// Frees all allocated memory
{
  int i;

# define CINN(x) do { if ((x)) { delete (x); (x) = NULL; } } while (0)
  // clear if not null

  for (i = 0; i < msgcount; i++)
    CINN(messages[i]);
  delete [] messages; // This is causing core dump???
  msgcount = 0;
  ...

# undef CINN

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