Create in C a dynamic 3D Array

Question

I have the following C code:

  char buffer[255];
  char ***data = NULL;
  int i = 0;
  int size = 10;

  **data = (char*) calloc(size, sizeof(char**));

  while(fgets(buffer, 255, database)) {
    if(i + 1 >= size) {
      size += 10;
      **data = (char*) realloc(**data, size*sizeof(char**));
    }

    char **line = str_split(buffer, ',', 6);
    **data[i++] = **line;
  }

I am a noob at C. And I do not rearly understand my code. But I want a 3D char array (in Java I woud say a 2D String array). The first [] are the lines from my textfile reading with 'fgets' from 'database' (and I don't know how many lines, thats why I want it dynamic). The second [] and thirt [] are filled with the values from str_split.

str_split works fine, thats the code:

char** str_split(char* str, const char a_delim, int count) {
  char **result;
  char  *token;
  char  *rest = str;
  char  delim[] = { a_delim, '\0' };

  result = (char**) malloc(sizeof(char*) * count);

  int i = 0;
  while((token = strtok_s(rest, delim, &rest))) {
    *(result + i++) = token;
  }

  return result;
}

So the problem is at run time I get the following error:

Access violation writing location 0x00000000.

What is wrong?

1) **data = (char*) calloc(size, sizeof(char**)); --> data = (char***) calloc(size, sizeof(char**)); — BLUEPIXY
– BLUEPIXY, Commented Jan 5, 2016 at 15:46
"I do not rearly understand my code": Then how did you write it? And where is this error occurring? — Scott Hunter
– Scott Hunter, Commented Jan 5, 2016 at 15:46
"I do not nearly understand my code" Well, that's frustrating. How can you expect others to understand it? — Eugene Sh.
– Eugene Sh., Commented Jan 5, 2016 at 15:46

Sorin · Accepted Answer · 2016-01-05 15:49:55Z

2

The first alloc should look like:

data = (char***) calloc(size, sizeof(char**));

Similar for realloc, and finally

data[i++] = line;

The problem is that you try to dereference data (**data) to assign it the value of the calloc, but data is null to begin with so you get access violation. In general you should make sure that a pointer is not null before you deference it.

answered Jan 5, 2016 at 15:49

Sorin

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