Use of char **

[MatejSlansky]

Hi everybody,
I'd like to ask for help with usage of char **. I have a following func, which dynamically allocates pointer a array

and pointers of char[] arrays in it:

int sptr(char **ppchr)
{
  int x = 0, ret = 0;
  char *pchr = NULL, **ptchr = NULL;
 
  // In place of for() you can imagine enumeration if something, quantity
  // of which is not known during design time. It's in extra func because
  // I'll need recursion (then I'll need extra parameter long *  for index
  // forward of course)
  for(x = 0; x < 10;x++)
  {
    // array of pointers allocation
    if((ptchr = (char **)realloc(ppchr, sizeof(char *) * (x + 1))) == NULL)
    {
      printf("ERR realloc\n");
      ret = 1;
      goto CleanExit;
    }
    ppchr = ptchr;
    // char[] allocation
    if((pchr = (char *)malloc(sizeof(char) * (11))) == NULL)
    {
      printf("ERR malloc\n");
      ret = 2;
      goto CleanExit;
    }
    memset(pchr, '\x0', sizeof(pchr));
    ppchr[x] = pchr;
    // fill out chararray
    sprintf(ppchr[x], "Item%d", x);
  }
 
CleanExit:
  // freeing is only done if an error occurs, otherwise it manages
  // 'upper' procedure after it processes contents
  if(ret)
  {
    for(x = 0; x < 10;x++)
      if(ppchr[x])
      {
        free(ppchr[x]);
      }
    free(ppchr);
  }
  return ret;
}

And now where my problem is: as far as everything including contents processing is in one single procedure, everything goes like a charm, but I need from sptr() allocations and fill out and then to give that array to some func, which needs char ** as a parameter.

So I moved declaration of **ppchr one level upper:

int main(int argc, char* argv[])
{
  char **ppchr = NULL;
  int x = 0, ret = 0;
 
  ret = sptr(ppchr);
 
  printf("sptr ret: %d\n", ret);
  for(x = 0; x < 10;x++)
  {
    printf("Contents %d=%s\n", x, ppchr[x]);
  }
 
  if(!ret)
  {
    for(x = 0; x < 10;x++)
    if(ppchr[x])
    {
      free(ppchr[x]);
    }
    if(ppchr)
      free(ppchr);
  }
  return 0;
}
 

.. and sudenly everything goes wrong :-(. Or I have mistake in that declaration or in way of passing the array to sptr(), but I just never get that array back to main(), it almost looks like I'm passing this way something absolutely different :-). Notice that number nor size of char items is not known before run time and that I really need to pass it later as char **. So please don't advise use of struct, which is way I'd normally go in this case.

Please explain what's wrong or how to make it work. I though that another way is not to pass initial char** pointer to sptr() and to return it instead (char **sptr(char *some_par()), however I just don't understand why the hell this doesn't work :-(

Please don't advise vectors nor CString etc. I want to make it work in C, because I want to UNDERSTAND it, which usage of vectors doesn't give me.

Thanks a lof for any help.

Mates

[newb16]

Add third '*' , like char *** ppchr; ... (*ppchr) = (char*) realloc( *ppchr, ... );
and in main program call it like ... ( &ppchr)

[weaknessforcats]

The argument ppchar is a COPY of the char** in main(). Any change to ppchar is a change to the COPY. The char** in main() is never altered.

To do do this you need the address of the char** in main(). That means
sptr() needs a char*** argument.

What I would do is have sptr() return a void* and then typecast that void * into the correct pointer type.