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 Table 51-1 and Table 51-2.
Note: The macros in Table 51-1 automatically return from your function, those in Table 51-2 only set the return value; they don't return from your function.
Table 51-1. 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. |
Table 51-2. 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.