Detailed explanation of the usage of PHP custom function return value

Return value

User spaceFunctionUse the return keyword to return information to its calling space, which is the same as the syntax of C language.

For example:

function sample_long() {  
  return 42;  
}  
$bar = sample_long();

When sample_long() is called, 42 is returned and set to the $bar variable. The equivalent code in C language is as follows:

int sample_long(void) {  
  return 42;  
}  
void main(void) {  
  int bar = sample_long();  
}

Of course, In C language you always know what the function being called is, and it returns based on the function prototype, so accordingly you have to define the variable where the return result is stored. When processed in PHP user space, the variable type is dynamic and relies on The type of zval introduced in Chapter 2 "Ins and Outs of Variables".

return_value variable

You may think that your internal function should directly return a zval , or allocate a zval's memory space and return zval as follows *.

PHP_FUNCTION(sample_long_wrong)  
{  
    zval *retval;  
      
    MAKE_STD_ZVAL(retval);  
    ZVAL_LONG(retval, 42);  
      
    return retval;  
}

Unfortunately, this is incorrect. It is not mandatory for every function implementation to allocate zval and return it. But the Zend engine Pre-allocate this space before the function call. Then initialize the type of zval to IS_NULL and pass the value as the parameter name return_value. The following is the correct approach:

PHP_FUNCTION(sample_long)  
{  
    ZVAL_LONG(return_value, 42);  
    return;  
}

It should be noted that the PHP_FUNCTION() implementation does not Any value will be returned directly. Instead, the appropriate data will be popped directly into the return_value parameter, and the Zend engine will process it after the internal function is executed.

Friendly reminder: ZVAL_LONG() macro is for multiple assignments A wrapper for the operation:

Z_TYPE_P(return_value) = IS_LONG;  
Z_LVAL_P(return_value) = 42;

Or more directly:

return_value->type = IS_LONG;  
return_value->value.lval = 42;

The is_ref and refcount attributes of return_value should not be modified directly by internal functions. These values ​​​​are handled by the Zend engine in Initialized and processed when your function is called.

Now let's take a look at this special function and add it to the sample extension created in Chapter 5, "Your First Extension". Just add it in Add this function below the sample_hello_world() function, and add sample_long() to the php_sample_functions structure:

static function_entry php_sample_functions[] = {  
    PHP_FE(sample_hello_world, NULL)  
    PHP_FE(sample_long, NULL)  
    { NULL, NULL, NULL }  
};

Now we can execute make to rebuild the extension.

If everything is OK, you can run php and test the new function:

$ php -r 'var_dump(sample_long());

Wrap more compact macros

In the code In terms of readability and maintainability, there are repeated parts in the ZVAL_*() macro: return_value variable. In this case, by replacing ZVAL of the macro with RETVAL, we can omit return_value when calling.

In the previous example, the implementation code of sample_long() can be reduced to the following:

PHP_FUNCTION(sample_long)  
{  
    RETVAL_LONG(42);  
    return;  
}

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