PHP数组实际占用内存大小原理解析

<?php 
  echo memory_get_usage() , '<br>'; 
  $start = memory_get_usage(); 
  $a = Array(); 
  for ($i=0; $i<1000; $i++) { 
  $a[$i] = $i + $i; 
  } 
  $mid = memory_get_usage(); 
  echo memory_get_usage() , '<br>'; 
  for ($i=1000; $i<2000; $i++) { 
  $a[$i] = $i + $i; 
  } 
  $end = memory_get_usage(); 
  echo memory_get_usage() , '<br>'; 
  echo 'argv:', ($mid - $start)/1000 ,'bytes' , '<br>'; 
  echo 'argv:',($end - $mid)/1000 ,'bytes' , '<br>'; 

#include "stdafx.h" 
//#include <stdio.h> 
  
int main() { 
    printf("int:%d\nlong:%d\ndouble:%d\nchar:%d\nsize_t:%d\n",  
    sizeof(int), sizeof(long),  
    sizeof(double), sizeof(char ),  
    sizeof(size_t)); 
  return  0;  
} 

typedef struct _zval_struct zval; 
struct _zval_struct { 
  / Variable information / 
  zvalue_value value;   / The value 1 12字节(32位机是12，64位机需要8+4+4=16) / 
  zend_uint refcount__gc; / The number of references to this value (for GC) 4字节 / 
  zend_uchar type;    / The active type 1字节/ 
  zend_uchar is_ref__gc; / Whether this value is a reference (&) 1字节/ 
}; 

typedef union _zvalue_value { 
  long lval;         / long value / 
  double dval;        / double value / 
  struct {          / string value / 
    char val; 
    int len; 
  } str;  
  HashTable ht;       / hash table value / 
  zend_object_value obj;   /object value / 
} zvalue_value; 

typedef struct _hashtable { 
  uint nTableSize;//4 
  uint nTableMask;//4 
  uint nNumOfElements;//4 
  ulong nNextFreeElement;//4 
  Bucket pInternalPointer;  / Used for element traversal 4/ 
  Bucket pListHead;//4 
  Bucket pListTail;//4 
  Bucket arBuckets;//4 
  dtor_func_t pDestructor;//4 
  zend_bool persistent;//1 
  unsigned char nApplyCount;//1 
  zend_bool bApplyProtection;//1 
#if ZEND_DEBUG 
  int inconsistent;//4 
#endif 
} HashTable; 

typedef struct bucket { 
  ulong h;  / Used for numeric indexing        4字节 / 
  uint nKeyLength;  / The length of the key (for string keys) 4字节 / 
  void pData;    / 4字节/ 
  void pDataPtr;     / 4字节/ 
  struct bucket pListNext; / PHP arrays are ordered. This gives the next element in that order4字节/ 
  struct bucket pListLast; / and this gives the previous element      4字节 / 
  struct bucket pNext;   / The next element in this (doubly) linked list   4字节/ 
  struct bucket pLast;   / The previous element in this (doubly) linked list   4字节/ 
  char arKey[1];      / Must be last element  1字节/ 
} Bucket;