Chapter 36. 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 Table 36-1 and Table 36-2.

Note: The macros in Table 36-1 automatically return from your function, those in Table 36-2 only set the return value; they don't return from your function.

Table 36-1. 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 36-2. 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.