Re: invalid conversion from void* to int**

From:
"Old Wolf" <oldwolf@inspire.net.nz>
Newsgroups:
comp.lang.c++
Date:
15 May 2006 19:47:16 -0700
Message-ID:
<1147747636.272646.24610@i40g2000cwc.googlegroups.com>
Martin J=F8rgensen wrote:

void *alloc_mem (size_t num_elems, size_t elem_size,
                   char *filename, int line,
                   size_t *total_mem)
{
    void *mem;
    size_t size = num_elems*elem_size;
    size += (sizeof (size_t) <= elem_size) ? elem_size
             : sizeof (size_t);


Why not just use sizeof(size_t) ?

    mem = malloc(size);

    if (!mem)
    {
      fprintf(stderr, "%s: line %d, malloc(%lu) failed.\n",
              filename, line, (unsigned long) size);
      exit(EXIT_FAILURE);
    }

    /* save memory allocated for this pointer */
    memcpy(((char *)mem)+num_elems*elem_size,
           &size, sizeof size);


What is the purpose of storing that size there?
How are you planning to access it in future?

    *total_mem += size; /* update total memory allocated untill now */


You should check here , and in the mutliplication above,
that you don't overflow a size_t .

    return mem;

}
- - - - - - - - - - - - - - - - - - - - - - - -

But I then declared some arrays like:

double **two_D_double;
int **two_D_int;
double *one_D_double;
int *one_D_int;


Those are pointers, not arrays.

etc. etc...

MS visual studio 2005 + gcc doesn't complain. But with g++ I get such an
error as:

"invalid conversion from void* to int**" (the same for double **)


You didn't post any code that would give that error.

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