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# 第 37章Returning Values

Returning values from your functions to PHP was described briefly in an earlier section; this section gives the details. Return values are passed via the return_value variable, which is passed to your functions as argument. The return_value argument consists of a zval container (see the earlier discussion of the call interface) that you can freely modify. The container itself is already allocated, so you don't have to run MAKE_STD_ZVAL on it. Instead, you can access its members directly.

To make returning values from functions easier and to prevent hassles with accessing the internal structures of the zval container, a set of predefined macros is available (as usual). These macros automatically set the correspondent type and value, as described in 表37-1 and 表37-2.

> 注意: The macros in 表37-1 automatically return from your function, those in 表37-2 only set the return value; they don't return from your function.

表 37-1. Predefined Macros for Returning Values from a Function

Macro | Description
RETURN_RESOURCE(resource) | Returns a resource.
RETURN_BOOL(bool) | Returns a Boolean.
RETURN_NULL() | Returns nothing (a NULL value).
RETURN_LONG(long) | Returns a long.
RETURN_DOUBLE(double) | Returns a double.
RETURN_STRING(string, duplicate) | Returns a string. The duplicate flag indicates whether the string should be duplicated using estrdup().
RETURN_STRINGL(string, length, duplicate) | Returns a string of the specified length; otherwise, behaves like RETURN_STRING. This macro is faster and binary-safe, however.
RETURN_EMPTY_STRING() | Returns an empty string.
RETURN_FALSE | Returns Boolean false.
RETURN_TRUE | Returns Boolean true.

表 37-2. Predefined Macros for Setting the Return Value of a Function

Macro | Description
RETVAL_RESOURCE(resource) | Sets the return value to the specified resource.
RETVAL_BOOL(bool) | Sets the return value to the specified Boolean value.
RETVAL_NULL | Sets the return value to NULL.
RETVAL_LONG(long) | Sets the return value to the specified long.
RETVAL_DOUBLE(double) | Sets the return value to the specified double.
RETVAL_STRING(string, duplicate) | Sets the return value to the specified string and duplicates it to Zend internal memory if desired (see also RETURN_STRING).
RETVAL_STRINGL(string, length, duplicate) | Sets the return value to the specified string and forces the length to become length (see also RETVAL_STRING). This macro is faster and binary-safe, and should be used whenever the string length is known.
RETVAL_EMPTY_STRING | Sets the return value to an empty string.
RETVAL_FALSE | Sets the return value to Boolean false.
RETVAL_TRUE | Sets the return value to Boolean true.

Complex types such as arrays and objects can be returned by using array_init() and object_init(), as well as the corresponding hash functions on return_value. Since these types cannot be constructed of trivial information, there are no predefined macros for them.

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