1/*
2*******************************************************************************
3*
4*   Copyright (C) 2002-2012, International Business Machines
5*   Corporation and others.  All Rights Reserved.
6*
7*******************************************************************************
8*/
9
10#ifndef STRENUM_H
11#define STRENUM_H
12
13#include "unicode/uobject.h"
14#include "unicode/unistr.h"
15
16/**
17 * \file
18 * \brief C++ API: String Enumeration
19 */
20
21U_NAMESPACE_BEGIN
22
23/**
24 * Base class for 'pure' C++ implementations of uenum api.  Adds a
25 * method that returns the next UnicodeString since in C++ this can
26 * be a common storage format for strings.
27 *
28 * <p>The model is that the enumeration is over strings maintained by
29 * a 'service.'  At any point, the service might change, invalidating
30 * the enumerator (though this is expected to be rare).  The iterator
31 * returns an error if this has occurred.  Lack of the error is no
32 * guarantee that the service didn't change immediately after the
33 * call, so the returned string still might not be 'valid' on
34 * subsequent use.</p>
35 *
36 * <p>Strings may take the form of const char*, const UChar*, or const
37 * UnicodeString*.  The type you get is determine by the variant of
38 * 'next' that you call.  In general the StringEnumeration is
39 * optimized for one of these types, but all StringEnumerations can
40 * return all types.  Returned strings are each terminated with a NUL.
41 * Depending on the service data, they might also include embedded NUL
42 * characters, so API is provided to optionally return the true
43 * length, counting the embedded NULs but not counting the terminating
44 * NUL.</p>
45 *
46 * <p>The pointers returned by next, unext, and snext become invalid
47 * upon any subsequent call to the enumeration's destructor, next,
48 * unext, snext, or reset.</p>
49 *
50 * ICU 2.8 adds some default implementations and helper functions
51 * for subclasses.
52 *
53 * @stable ICU 2.4
54 */
55class U_COMMON_API StringEnumeration : public UObject {
56public:
57    /**
58     * Destructor.
59     * @stable ICU 2.4
60     */
61    virtual ~StringEnumeration();
62
63    /**
64     * Clone this object, an instance of a subclass of StringEnumeration.
65     * Clones can be used concurrently in multiple threads.
66     * If a subclass does not implement clone(), or if an error occurs,
67     * then NULL is returned.
68     * The clone functions in all subclasses return a base class pointer
69     * because some compilers do not support covariant (same-as-this)
70     * return types; cast to the appropriate subclass if necessary.
71     * The caller must delete the clone.
72     *
73     * @return a clone of this object
74     *
75     * @see getDynamicClassID
76     * @stable ICU 2.8
77     */
78    virtual StringEnumeration *clone() const;
79
80    /**
81     * <p>Return the number of elements that the iterator traverses.  If
82     * the iterator is out of sync with its service, status is set to
83     * U_ENUM_OUT_OF_SYNC_ERROR, and the return value is zero.</p>
84     *
85     * <p>The return value will not change except possibly as a result of
86     * a subsequent call to reset, or if the iterator becomes out of sync.</p>
87     *
88     * <p>This is a convenience function. It can end up being very
89     * expensive as all the items might have to be pre-fetched
90     * (depending on the storage format of the data being
91     * traversed).</p>
92     *
93     * @param status the error code.
94     * @return number of elements in the iterator.
95     *
96     * @stable ICU 2.4 */
97    virtual int32_t count(UErrorCode& status) const = 0;
98
99    /**
100     * <p>Returns the next element as a NUL-terminated char*.  If there
101     * are no more elements, returns NULL.  If the resultLength pointer
102     * is not NULL, the length of the string (not counting the
103     * terminating NUL) is returned at that address.  If an error
104     * status is returned, the value at resultLength is undefined.</p>
105     *
106     * <p>The returned pointer is owned by this iterator and must not be
107     * deleted by the caller.  The pointer is valid until the next call
108     * to next, unext, snext, reset, or the enumerator's destructor.</p>
109     *
110     * <p>If the iterator is out of sync with its service, status is set
111     * to U_ENUM_OUT_OF_SYNC_ERROR and NULL is returned.</p>
112     *
113     * <p>If the native service string is a UChar* string, it is
114     * converted to char* with the invariant converter.  If the
115     * conversion fails (because a character cannot be converted) then
116     * status is set to U_INVARIANT_CONVERSION_ERROR and the return
117     * value is undefined (though not NULL).</p>
118     *
119     * Starting with ICU 2.8, the default implementation calls snext()
120     * and handles the conversion.
121     * Either next() or snext() must be implemented differently by a subclass.
122     *
123     * @param status the error code.
124     * @param resultLength a pointer to receive the length, can be NULL.
125     * @return a pointer to the string, or NULL.
126     *
127     * @stable ICU 2.4
128     */
129    virtual const char* next(int32_t *resultLength, UErrorCode& status);
130
131    /**
132     * <p>Returns the next element as a NUL-terminated UChar*.  If there
133     * are no more elements, returns NULL.  If the resultLength pointer
134     * is not NULL, the length of the string (not counting the
135     * terminating NUL) is returned at that address.  If an error
136     * status is returned, the value at resultLength is undefined.</p>
137     *
138     * <p>The returned pointer is owned by this iterator and must not be
139     * deleted by the caller.  The pointer is valid until the next call
140     * to next, unext, snext, reset, or the enumerator's destructor.</p>
141     *
142     * <p>If the iterator is out of sync with its service, status is set
143     * to U_ENUM_OUT_OF_SYNC_ERROR and NULL is returned.</p>
144     *
145     * Starting with ICU 2.8, the default implementation calls snext()
146     * and handles the conversion.
147     *
148     * @param status the error code.
149     * @param resultLength a ponter to receive the length, can be NULL.
150     * @return a pointer to the string, or NULL.
151     *
152     * @stable ICU 2.4
153     */
154    virtual const UChar* unext(int32_t *resultLength, UErrorCode& status);
155
156    /**
157     * <p>Returns the next element a UnicodeString*.  If there are no
158     * more elements, returns NULL.</p>
159     *
160     * <p>The returned pointer is owned by this iterator and must not be
161     * deleted by the caller.  The pointer is valid until the next call
162     * to next, unext, snext, reset, or the enumerator's destructor.</p>
163     *
164     * <p>If the iterator is out of sync with its service, status is set
165     * to U_ENUM_OUT_OF_SYNC_ERROR and NULL is returned.</p>
166     *
167     * Starting with ICU 2.8, the default implementation calls next()
168     * and handles the conversion.
169     * Either next() or snext() must be implemented differently by a subclass.
170     *
171     * @param status the error code.
172     * @return a pointer to the string, or NULL.
173     *
174     * @stable ICU 2.4
175     */
176    virtual const UnicodeString* snext(UErrorCode& status);
177
178    /**
179     * <p>Resets the iterator.  This re-establishes sync with the
180     * service and rewinds the iterator to start at the first
181     * element.</p>
182     *
183     * <p>Previous pointers returned by next, unext, or snext become
184     * invalid, and the value returned by count might change.</p>
185     *
186     * @param status the error code.
187     *
188     * @stable ICU 2.4
189     */
190    virtual void reset(UErrorCode& status) = 0;
191
192    /**
193     * Compares this enumeration to other to check if both are equal
194     *
195     * @param that The other string enumeration to compare this object to
196     * @return TRUE if the enumerations are equal. FALSE if not.
197     * @stable ICU 3.6
198     */
199    virtual UBool operator==(const StringEnumeration& that)const;
200    /**
201     * Compares this enumeration to other to check if both are not equal
202     *
203     * @param that The other string enumeration to compare this object to
204     * @return TRUE if the enumerations are equal. FALSE if not.
205     * @stable ICU 3.6
206     */
207    virtual UBool operator!=(const StringEnumeration& that)const;
208
209protected:
210    /**
211     * UnicodeString field for use with default implementations and subclasses.
212     * @stable ICU 2.8
213     */
214    UnicodeString unistr;
215    /**
216     * char * default buffer for use with default implementations and subclasses.
217     * @stable ICU 2.8
218     */
219    char charsBuffer[32];
220    /**
221     * char * buffer for use with default implementations and subclasses.
222     * Allocated in constructor and in ensureCharsCapacity().
223     * @stable ICU 2.8
224     */
225    char *chars;
226    /**
227     * Capacity of chars, for use with default implementations and subclasses.
228     * @stable ICU 2.8
229     */
230    int32_t charsCapacity;
231
232    /**
233     * Default constructor for use with default implementations and subclasses.
234     * @stable ICU 2.8
235     */
236    StringEnumeration();
237
238    /**
239     * Ensures that chars is at least as large as the requested capacity.
240     * For use with default implementations and subclasses.
241     *
242     * @param capacity Requested capacity.
243     * @param status ICU in/out error code.
244     * @stable ICU 2.8
245     */
246    void ensureCharsCapacity(int32_t capacity, UErrorCode &status);
247
248    /**
249     * Converts s to Unicode and sets unistr to the result.
250     * For use with default implementations and subclasses,
251     * especially for implementations of snext() in terms of next().
252     * This is provided with a helper function instead of a default implementation
253     * of snext() to avoid potential infinite loops between next() and snext().
254     *
255     * For example:
256     * \code
257     * const UnicodeString* snext(UErrorCode& status) {
258     *   int32_t resultLength=0;
259     *   const char *s=next(&resultLength, status);
260     *   return setChars(s, resultLength, status);
261     * }
262     * \endcode
263     *
264     * @param s String to be converted to Unicode.
265     * @param length Length of the string.
266     * @param status ICU in/out error code.
267     * @return A pointer to unistr.
268     * @stable ICU 2.8
269     */
270    UnicodeString *setChars(const char *s, int32_t length, UErrorCode &status);
271};
272
273U_NAMESPACE_END
274
275/* STRENUM_H */
276#endif
277