After leaving the function my array is empty

Question

In a previous question (changing value from function) I got help, which lead me to the next problem:

I used a string split and then a simple copy

int Crawl :: splitUrl(char ***arr, int max_length, char *url)
{
   int idx=0;
   char * p;
   int i;

  p = strtok (url,"/"); // call the strtok with str as 1st arg for the 1st time.
    while (p != NULL && idx < max_length)
    {
       for (i=0;i<maxUrlSize-1 && p[i] != '\0';i++)
          (*arr)[idx][i] = p[i];
       for ( ; i< maxUrlSize-1;i++)
          (*arr)[idx][i] = '\0';

        printf("tmp[idx[%d]] %s  %d addr: %x\n",idx,(*arr)[idx],strlen(p),(*arr)[idx]);

        idx++;
        p = strtok (NULL, "/");
    }

The array is allocated:

 split_url = new char * [ maxUrlSplit ];
 printf("split_url %x\n",split_url);
 for (i=0;i<maxUrlSplit;i++)
  {
     split_url[ i ] = new char [ maxUrlSize ];
     printf("split_url[ %d ] %x\n",i,split_url[i]);
  }

and after the function i used a loop to get all elements in the arry. i printet it like

printf("add: %x %s %d\n",split_url[iarr], split_url[iarr], strlen(split_url[iarr]));

The address is always the same, but after the function runs there are no entries?

I run the function like

  int arr_size = crawl->splitUrl(&split_url,maxUrlSplit,url);

GDB and Valgrind don't say anything.

Please add code showing *exactly* how `split_url` is passed to the function. — Oliver Charlesworth, May 02 '11 at 15:51
If you have `***` in your code, you are doing it wrong. Stop it. — Benjamin Lindley, May 02 '11 at 15:54
@Oli done @Benjamin what did you mean ? i think i should be call by reference ? :-/ — Roby, May 02 '11 at 15:55
@Benjamin: In C++, this is almost certainly the case! In C, it's perhaps possible that you're dealing with multi-dimensional arrays, in which case it *could* be reasonable. — Oliver Charlesworth, May 02 '11 at 15:56
When you realize you are doing some [three star programming](http://c2.com/cgi/wiki?ThreeStarProgrammer), you should probably try to rework your design. — Null Set, May 02 '11 at 15:56
@Roby: I mean, use the standard library facilities that are provided for you. If you want an array of strings, the correct data structure to use is `std::vector`, not `char**`. — Benjamin Lindley, May 02 '11 at 15:59
@Benjamin hmm... the next time i will do it :P but why doesnt work it :( — Roby, May 02 '11 at 16:00
You have printfs in there, why don't you tell us how many runs of the loops you get etc. — AndreasT, May 02 '11 at 16:01
because its not a fixed site but atm its 25times... last time i postet to mutch code so i tried to remove the unimportant stuff :-/ — Roby, May 02 '11 at 16:03

Oliver Charlesworth · Accepted Answer · 2011-05-02T16:06:38.573

After I made your code compilable, it worked "fine", at least in the sense that it outputs the expected result. I make no comment on style or safety:

const int maxUrlSplit = 10;
const int maxUrlSize = 64;


int splitUrl(char ***arr, int max_length, char *url)
{
   int idx=0;
   char * p;
   int i;

  p = strtok (url,"/"); // call the strtok with str as 1st arg for the 1st time.
    while (p != NULL && idx < max_length)
    {
       for (i=0;i<maxUrlSize-1 && p[i] != '\0';i++)
          (*arr)[idx][i] = p[i];
       for ( ; i< maxUrlSize-1;i++)
          (*arr)[idx][i] = '\0';

        printf("tmp[idx[%d]] %s  %d addr: %x\n",idx,(*arr)[idx],strlen(p),(*arr)[idx]);

        idx++;
        p = strtok (NULL, "/");
    }
    return idx;
}

int main()
{
    char url[] = "ant/bison/chimp";

    int i;
    char **split_url = new char * [ maxUrlSplit ];
    printf("split_url %x\n",split_url);
    for (i=0;i<maxUrlSplit;i++)
    {
        split_url[ i ] = new char [ maxUrlSize ];
        printf("split_url[ %d ] %x\n",i,split_url[i]);
    }
    int arr_size = splitUrl(&split_url,maxUrlSplit,url);

    for (i = 0; i < arr_size; i++)
    {
        printf("add: %x %s %d\n",split_url[i], split_url[i], strlen(split_url[i]));
    }
}

Output:

split_url 2f1490
split_url[ 0 ] 2f14e8
split_url[ 1 ] 2f1558
split_url[ 2 ] 2f15c8
split_url[ 3 ] 2f1638
split_url[ 4 ] 2f16a8
split_url[ 5 ] 2f1718
split_url[ 6 ] 2f1788
split_url[ 7 ] 2f17f8
split_url[ 8 ] 2f1868
split_url[ 9 ] 2f18d8
tmp[idx[0]] ant  3 addr: 2f14e8
tmp[idx[1]] bison  5 addr: 2f1558
tmp[idx[2]] chimp  5 addr: 2f15c8
*************
add: 2f14e8 ant 3
add: 2f1558 bison 5
add: 2f15c8 chimp 5

Therefore, you must have some other issue in some other part of your code.

@Roby: Explain what? You do `split_url[ i ] = new char [ maxUrlSize ];` but then you don't do anything with it. — Oliver Charlesworth, May 02 '11 at 15:44
@Roby: Ok. Please put your *actual* code in the question, so that we don't have to guess. — Oliver Charlesworth, May 02 '11 at 15:46
UIIII THX, but where is the problem ? i just could be a memory leak ? write out of memory ? or what — Roby, May 02 '11 at 16:09
@Roby: I have no idea. Your code works for me. You haven't given enough us enough information to figure it out. Try reducing your code to a *complete*, *minimal*, *compilable* example (see http://sscce.org) that demonstrates the problem, not just snippets. But seriously, if you're working in C++, switch to using `std::string` and `std::vector`, etc. It will make your life 10x easier. — Oliver Charlesworth, May 02 '11 at 16:10
@Oil: i think i will wrote it to c++... atm it really sucks.... but VERRY BIG THANKS to all — Roby, May 02 '11 at 16:14

score 0 · Answer 2 · edited May 23 '17 at 12:12

Ok, to get the obvious out of the way: Use Boost Tokenizer or the standard lib as beautifully explained in another so question.

Trying to fix what is there:

// pass in max_length as reference, or pointer, so you can change it.
// no three stars! You are passing in an adress, the extra indirection
// is not necessary (at least as far as I see it...

int Crawl :: splitUrl(char **arr, int & max_length, char *url)
{
   int idx=0;
   char * p;
   int i;

   p = strtok (url,"/"); // call the strtok with str as 1st arg for the 1st time.
   while (p != NULL && idx < max_length)
   {
     strcopy(arr[idx], p);
     // note you could also do if you absolutely KNOW that you won't deallocate url!
     // arr[idx] = p;
     idx++;
     p = strtok (NULL, "/");
   }
   max_length = idx; // no filling the rest with empty strings....
 }

but max_length is the max length of the array so i dont want more than max_length examples — Roby, May 02 '11 at 16:44

After leaving the function my array is empty

2 Answers2