Question

I’m trying to build a char array for storing the return value of a function. In the following function the data is stored in *****valv**. How to build a extern variable to access the data?

int credis_lrange(REDIS rhnd, const char *key, 
                   int start, int end, char ***valv) 
{
  int rc;

  if ((rc = cr_sendfandreceive(rhnd, CR_MULTIBULK, "LRANGE %s %d %d\r\n", 
                                key, start, end)) == 0) 
  {
    *valv = rhnd->reply.multibulk.bulks;
    rc = rhnd->reply.multibulk.len;
  }

  return rc;
}

Solution:

char **elements;

int size = credis_lrange(this->redis,"object_2",600,603,&elements);

for (int i=0; i<size;i++) {
    cout << "element: " << elements[i] << endl; 
}

Thanks to everyone!

Answer 1

char ***element[size];

Is not exactly a 3D array, but an array of size elements of pointers-to-pointers-to-pointers to char.

Use any one of the following:

char e[ D1 ][ D2 ][ D3 ]; /* D1, D2, D3 are integral constants */
char *e[ D2 ][ D3 ];
char e[][ D2 ][ D3 ];

Also, you can pass it on by simply speficying e as the argument to your function.

On further reading, it appears that the parameter is not really a 3D array but a pointer to an array of C-style strings. Note, the syntax may be the same, the intent is different.

In that case, you’ll need to do two things:

• Specify the number of strings you want to store in the array
• For each string
  • Allocate memory
  • Copy string data to the char array

And finally, you’ll be passing in the address of this array of strings on to the credis_lrange function.