The model is that the enumeration is over strings maintained by * a 'service.' At any point, the service might change, invalidating * the enumerator (though this is expected to be rare). The iterator * returns an error if this has occurred. Lack of the error is no * guarantee that the service didn't change immediately after the * call, so the returned string still might not be 'valid' on * subsequent use.
* *Strings may take the form of const char*, const char16_t*, or const * UnicodeString*. The type you get is determine by the variant of * 'next' that you call. In general the StringEnumeration is * optimized for one of these types, but all StringEnumerations can * return all types. Returned strings are each terminated with a NUL. * Depending on the service data, they might also include embedded NUL * characters, so API is provided to optionally return the true * length, counting the embedded NULs but not counting the terminating * NUL.
* *The pointers returned by next, unext, and snext become invalid * upon any subsequent call to the enumeration's destructor, next, * unext, snext, or reset.
* * ICU 2.8 adds some default implementations and helper functions * for subclasses. * * @stable ICU 2.4 */ class U_COMMON_API StringEnumeration : public UObject { public: /** * Destructor. * @stable ICU 2.4 */ virtual ~StringEnumeration(); /** * Clone this object, an instance of a subclass of StringEnumeration. * Clones can be used concurrently in multiple threads. * If a subclass does not implement clone(), or if an error occurs, * then NULL is returned. * The caller must delete the clone. * * @return a clone of this object * * @see getDynamicClassID * @stable ICU 2.8 */ virtual StringEnumeration *clone() const; /** *Return the number of elements that the iterator traverses. If * the iterator is out of sync with its service, status is set to * U_ENUM_OUT_OF_SYNC_ERROR, and the return value is zero.
* *The return value will not change except possibly as a result of * a subsequent call to reset, or if the iterator becomes out of sync.
* *This is a convenience function. It can end up being very * expensive as all the items might have to be pre-fetched * (depending on the storage format of the data being * traversed).
* * @param status the error code. * @return number of elements in the iterator. * * @stable ICU 2.4 */ virtual int32_t count(UErrorCode& status) const = 0; /** *Returns the next element as a NUL-terminated char*. If there * are no more elements, returns NULL. If the resultLength pointer * is not NULL, the length of the string (not counting the * terminating NUL) is returned at that address. If an error * status is returned, the value at resultLength is undefined.
* *The returned pointer is owned by this iterator and must not be * deleted by the caller. The pointer is valid until the next call * to next, unext, snext, reset, or the enumerator's destr