// Using the heap for memory allocation

#include "mem_syms.h"
#define ADDR DEC

void setup() {
  // a pointer to an int
  long int * x_p;
  // a pointer to a char
  char * y_p;

  // to keep track of where the heap starts and ends for us
  // there might already be stuff on the heap, which we want to
  // ignore.
  char * hs;
  char * he;
  char * p;
  
  Serial.begin(9600);
    
  Serial.println("MEM07");
  
  Serial.print("Avail mem:");  Serial.println(AVAIL_MEM, DEC);
  Serial.print("Heap starts at:");  Serial.println((unsigned int) HEAP_START, ADDR);
  Serial.print("Heap ends at:");  Serial.println((unsigned int) HEAP_END, ADDR);
  
  /* allocate memory for an int from the heap and remember its address
     we could say:
     x_p = (int *) malloc(sizeof(int));
     but then if we changed the type of x_p we would probably forget
     to fix the malloc call and things would break, subtly and horribly
     So instead we use the typeof and sizeof compiler operators
  */
  
  Serial.print("Allocate a chunk, size:");
  Serial.println(sizeof(*x_p));

  hs = HEAP_END;
  x_p = (typeof(x_p)) malloc(sizeof(*x_p));
  
  // why is this an inefficeint use of memory?
  //X y_p = (typeof(y_p)) malloc(sizeof(*y_p));

  he = HEAP_END;
 
  // if x_p == 0, the null pointer value, then malloc failed

  Serial.print("Avail mem:");  Serial.println(AVAIL_MEM, DEC);
  Serial.print("Heap starts at:");  Serial.println((unsigned int) HEAP_START, ADDR);
  Serial.print("Heap ends at:");  Serial.println( (unsigned int) HEAP_END, ADDR);

 
  // why did we use 2 bytes from the heap more than we expect for x_p?
  
  *x_p = 0x89abcdef;
  Serial.print("x_p:");
  Serial.println( (unsigned int) x_p, ADDR);
  Serial.print("*x_p:");
  Serial.println( (unsigned int) *x_p, HEX);
  
  Serial.print("y_p:");
  Serial.println( (unsigned int) y_p, ADDR);

  //Y *y_p = 'H';
  
  Serial.print("*y_p:");
  Serial.println(*y_p);


  // print the contents of the heap we just allocated from
  
  Serial.print("Heap:");
  for ( p = hs; p < he; p++) {
    unsigned char c = *p;
    Serial.print( c, HEX );
    Serial.print(" ");
  }
  Serial.println();
    
 }

void loop() {
}