PHP Global variables: PHP source code Analysis-Weak type variable implementation

PHP is a weakly typed, dynamic language script. When declaring a variable, you do not need to indicate the type of data it holds.
For example:
<?php
$var = 1;
$var = "variable";
$var = 1.00;
$var = Array ();
$var = new Object ();
Dynamic variables, which can be changed during run time, and do not need to declare variable types before use.
So, question one, how does the Zend engine implement this weak type in C?
In fact, the variables declared in PHP are saved in ze by structural zval.
First we open zend/zend.h to see the definition of Zval:
typedef struct _ZVAL_STRUCT Zval;
struct _zval_struct {
/* Variable Information * *
Zvalue_value value; /* Value * *
Zend_uint refcount__gc;
Zend_uchar type; /* Active type */
Zend_uchar is_ref__gc;
};
typedef Union _ZVALUE_VALUE {
Long lval; /* Long Value * *
Double Dval; /* Double Value * *
struct {
Char *val;
int Len;
} str;
HashTable *ht; /* Hash Table value * *
Zend_object_value obj;
} Zvalue_value;
Zend/zend_types.h:
typedef unsigned char Zend_bool;
typedef unsigned char Zend_uchar;
typedef unsigned int zend_uint;
typedef unsigned long Zend_ulong;
typedef unsigned short Zend_ushort;
From the above code, you can see that _zvalue_value is a key part of really saving data. A weakly typed variable declaration implemented by a common body
Question two, Zend engine is how to identify, storage PHP in a variety of data types?
_zval_struct.type stores the true type of a variable, depending on the type to choose how to get the Zvalue_value value.
Type value list (zend/zend.h):
#define IS_NULL 0
#define Is_long 1
#define Is_double 2
#define Is_bool 3
#define Is_array 4
#define IS_OBJECT 5
#define Is_string 6
#define Is_resource 7
#define Is_constant 8
#define Is_constant_array 9
Let's look at a simple example:
<?php
$a = 1;
At this time Zval.type = Is_long, then zval.value to take lval.
$a = array ();
At this point zval.type = Is_array, then zval.value to pick Ht.
One of the most complex of these is the "resource type" that is often needed in developing third-party extensions.
In PHP, any variable that is not part of PHP's built-in variable type is considered a resource for saving. This article links http://www.cxybl.com/html/wlbc/Php/20121213/34971.html