PHP in-depth learning variable reference counting

What is the reference count of php variables? First, let’s take a look at the underlying structure of PHP variables:

<code>typedef <span>struct</span> _zval_struct zval;
<span>struct</span> _zval_struct {
    zvalue_value <span>value</span>;     <span>//存放value</span>
    zend_uint refcount__gc;     <span>//引用计数</span>
    zend_uchar type;     <span>//判断类型</span>
    zend_uchar is_ref__gc;     <span>//是否被引用</span>
};
</code>

When we declare a variable in the PHP program, the zend engine will instantiate a zval structure, which has four member variables. Among them, type is used to determine what type this variable is; value is used to store actual data. In fact, value is also a structure, and I will not go into details here. Today we will focus on: the usefulness of the two fields refcount_gc and is_ref_gc. Suppose there is such a piece of code:

<code><span>$a</span> = <span>123</span>;
<span>$b</span> = <span>$a</span>;
</code>

Due to a simple int type variable, PHP has to instantiate a structure. In the case above, in fact, a is the same as

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The above introduces the reference counting of variables in PHP in-depth learning, including aspects of the content. I hope it will be helpful to friends who are interested in PHP tutorials.