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HomeBackend DevelopmentPHP TutorialPHP扩展开发 函数返回值未使用后报错的实现原理

在看PHP扩展开发时,看到一处关于PHP函数返回值的问题。

当定义了一个函数,而这个函数拥有返回值,在用户使用时,并没有使用返回值,zend引擎可以实现报错,这是如何实现的,怎么个原理?

<code>ZEND_FUNCTION(sample_array_range)
{
    if (return_value_used) {
        int i;

        //把返回值初始化成一个PHP语言中的数组
        array_init(return_value);
        for(i = 0; i </code>

在这个函数定义里面,感觉是先接收return_value_used参数,但是当函数运行完成之前,系统应该并不知道该函数返回值是否被使用到了吧!想不通他的实现原理。

求大牛,说说其中的实现原理!

回复内容:

在看PHP扩展开发时,看到一处关于PHP函数返回值的问题。

当定义了一个函数,而这个函数拥有返回值,在用户使用时,并没有使用返回值,zend引擎可以实现报错,这是如何实现的,怎么个原理?

<code>ZEND_FUNCTION(sample_array_range)
{
    if (return_value_used) {
        int i;

        //把返回值初始化成一个PHP语言中的数组
        array_init(return_value);
        for(i = 0; i </code>

在这个函数定义里面,感觉是先接收return_value_used参数,但是当函数运行完成之前,系统应该并不知道该函数返回值是否被使用到了吧!想不通他的实现原理。

求大牛,说说其中的实现原理!

实现原理其实很简单,在php代码被逐句解释之前,zend引擎实际上做了很多事情,比如说read、parser、compile、cache等等。

这里的return_value_used实际上是在compile阶段产生的,代码变成语法树之后,每个opline都会有一个_znode的结构体,用于保存当前节点的信息,定义如下:

<code>c</code><code>typedef struct _znode {
    int op_type;
    union {
        zval constant;

        zend_uint var;
        zend_uint opline_num; /*  Needs to be signed */
        zend_op_array *op_array;
        zend_op *jmp_addr;
        struct {
            zend_uint var;  /* dummy */
            zend_uint type;
        } EA;
    } u;
} znode;
</code>

这里内连了一个结构体EA,其中的type就保存了是否被接受的信息。

在compile阶段,他会凭借语法树来动态改变相应的值,比如$a = abc();和abc();和add(abc());都会执行不同的compile 函数,在某些情况下,EA.type会被标识为EXT_TYPE_UNUSED,如果有语法错误,它也能在执行之前就知道。

这里有zend的一份compile.c代码,你可以看一下它里面的各种函数,是针对不同的操作符进行不同处理的。

http://www.opensource.apple.com/source/apache_mod_php/apache_mod_php-4...

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