PHP variable principle, PHP variable _php tutorial

PHP variable principle, PHP variable

1.php, as a weakly typed language, does not need to explicitly indicate the type of the variable, but the PHP variable is also of type, and the PHP variable contains the following 8 variables (three major categories)

A. Scalar type: boolean,integer,float (double), string

B. Composite type: Array,object

C. Special type: Resource,null

2.php the principle of using C language to implement variables

A. Variable storage structure

typedef struct _ZVAL_STRUCT zval;...struct _zval_struct {/    * Variable information */    zvalue_value value;     /* The value of the stored variable is a reference count of the Union type */    zend_uint refcount__gc;/* variable, which defaults to 1*/    Zend_uchar type;    /* Variable type, for Is_null, Is_bool, Is_long, is_double, is_string, Is_array, Is_object, and Is_resource */    Zend_uchar is_ref__ gc;/* Indicates whether it is a reference */};

B. Storage variables are worth Zvalue_value as follows

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;

The union instead of the struct is used here to save memory space, assuming that a variable can only represent one type at a time

Reference: tipi open source Project Http://www.php-internals.com/book/?p=chapt03/03-01-00-variables-structure

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