/* 
 *
 * Originally from Appendix A of Advanced Linux Programming by
 * Mitchell, Oldham, and Samuel
 * New Riders Publishing, 2001
 *
 */

/* Use C's dynamic memory allocation functions.  */ 

/* Invoke the program using one command-line argument specifying the 
   size of an array.  This array consists of pointers to (possibly) 
   allocated arrays. 

   When the programming is running, select among the following 
   commands: 

   o allocate memory:   a <index> <memory-size> 
   o deallocate memory: d <index> 
   o read from memory:  r <index> <position-within-allocation> 
   o write to  memory:  w <index> <position-within-allocation> 
   o quit:              q 

   The user is responsible for obeying (or disobeying) the rules on dynamic 
   memory use.  */ 

#ifdef MTRACE 
#include <mcheck.h> 
#endif /* MTRACE */ 
#include <stdio.h> 
#include <stdlib.h> 
#include <assert.h> 

/* Allocate memory with the specified  size, returning nonzero upon 
   success.  */ 

void allocate (char** array, size_t size) 
{
  *array = malloc (size); 
} 

/* Deallocate memory.  */ 

void deallocate (char** array) 
{
  free ((void*) *array); 
} 

/* Read from a position in memory.  */ 

void read_from_memory (char* array, int position) 
{
  char character = array[position]; 

  if (character) 
    ; // do nothing
} 

/* Write to a position in memory.  */ 

void write_to_memory (char* array, int position) 
{
  array[position] = 'a'; 
} 

int main (int argc, char* argv[]) 
{
  char** array; 
  unsigned array_size; 
  char command[32]; 
  unsigned array_index; 
  char command_letter; 
  int size_or_position; 
  int error = 0; 

#ifdef MTRACE 
  mtrace (); 
#endif /* MTRACE  */ 

  if (argc != 2) {
    fprintf (stderr, "%s: array-size\n", argv[0]); 
    return 1; 
  } 

  array_size = strtoul (argv[1], 0, 0); 
  array = (char **) calloc (array_size, sizeof (char *)); 
  assert (array != 0); 

  /* Follow the user's commands.  */ 
  while (!error) {
    printf ("Please enter a command: "); 
    command_letter = getchar (); 
    assert (command_letter != EOF); 
    switch (command_letter) {

    case 'a': 
      fgets (command, sizeof (command), stdin); 
      if (sscanf (command, "%u %i", &array_index, &size_or_position) == 2 
          && array_index < array_size) 
     allocate (&(array[array_index]), size_or_position); 
   else 
     error = 1; 
   break; 

  case 'd': 
    fgets (command, sizeof (command), stdin); 
    if (sscanf (command, "%u", &array_index) == 1 
        && array_index < array_size) 
      deallocate (&(array[array_index])); 
    else 
      error = 1; 
    break; 

  case 'r': 
    fgets (command, sizeof (command), stdin); 
    if (sscanf (command, "%u %i", &array_index, &size_or_position) == 2 
        && array_index < array_size) 
      read_from_memory (array[array_index], size_or_position); 
    else 
      error = 1; 
    break; 

  case 'w': 
    fgets (command, sizeof (command), stdin); 
    if (sscanf (command, "%u %i", &array_index, &size_or_position) == 2 
        && array_index < array_size) 
      write_to_memory (array[array_index], size_or_position); 
    else 
      error = 1; 
    break; 

  case 'q': 
    free ((void *) array); 
    return 0; 

  default: 
    error = 1; 
  } 
} 

 free ((void *) array); 
 return 1; 
}