1// © 2016 and later: Unicode, Inc. and others.
2// License & terms of use: http://www.unicode.org/copyright.html
3/*
4*******************************************************************************
5*
6*   Copyright (C) 2002-2012, International Business Machines
7*   Corporation and others.  All Rights Reserved.
8*
9*******************************************************************************
10*/
11
12#ifndef STRENUM_H
13#define STRENUM_H
14
15#include "unicode/uobject.h"
16#include "unicode/unistr.h"
17
18/**
19 * \file
20 * \brief C++ API: String Enumeration
21 */
22
23U_NAMESPACE_BEGIN
24
25/**
26 * Base class for 'pure' C++ implementations of uenum api.  Adds a
27 * method that returns the next UnicodeString since in C++ this can
28 * be a common storage format for strings.
29 *
30 * <p>The model is that the enumeration is over strings maintained by
31 * a 'service.'  At any point, the service might change, invalidating
32 * the enumerator (though this is expected to be rare).  The iterator
33 * returns an error if this has occurred.  Lack of the error is no
34 * guarantee that the service didn't change immediately after the
35 * call, so the returned string still might not be 'valid' on
36 * subsequent use.</p>
37 *
38 * <p>Strings may take the form of const char*, const char16_t*, or const
39 * UnicodeString*.  The type you get is determine by the variant of
40 * 'next' that you call.  In general the StringEnumeration is
41 * optimized for one of these types, but all StringEnumerations can
42 * return all types.  Returned strings are each terminated with a NUL.
43 * Depending on the service data, they might also include embedded NUL
44 * characters, so API is provided to optionally return the true
45 * length, counting the embedded NULs but not counting the terminating
46 * NUL.</p>
47 *
48 * <p>The pointers returned by next, unext, and snext become invalid
49 * upon any subsequent call to the enumeration's destructor, next,
50 * unext, snext, or reset.</p>
51 *
52 * ICU 2.8 adds some default implementations and helper functions
53 * for subclasses.
54 *
55 * @stable ICU 2.4
56 */
57class U_COMMON_API StringEnumeration : public UObject {
58public:
59    /**
60     * Destructor.
61     * @stable ICU 2.4
62     */
63    virtual ~StringEnumeration();
64
65    /**
66     * Clone this object, an instance of a subclass of StringEnumeration.
67     * Clones can be used concurrently in multiple threads.
68     * If a subclass does not implement clone(), or if an error occurs,
69     * then NULL is returned.
70     * The clone functions in all subclasses return a base class pointer
71     * because some compilers do not support covariant (same-as-this)
72     * return types; cast to the appropriate subclass if necessary.
73     * The caller must delete the clone.
74     *
75     * @return a clone of this object
76     *
77     * @see getDynamicClassID
78     * @stable ICU 2.8
79     */
80    virtual StringEnumeration *clone() const;
81
82    /**
83     * <p>Return the number of elements that the iterator traverses.  If
84     * the iterator is out of sync with its service, status is set to
85     * U_ENUM_OUT_OF_SYNC_ERROR, and the return value is zero.</p>
86     *
87     * <p>The return value will not change except possibly as a result of
88     * a subsequent call to reset, or if the iterator becomes out of sync.</p>
89     *
90     * <p>This is a convenience function. It can end up being very
91     * expensive as all the items might have to be pre-fetched
92     * (depending on the storage format of the data being
93     * traversed).</p>
94     *
95     * @param status the error code.
96     * @return number of elements in the iterator.
97     *
98     * @stable ICU 2.4 */
99    virtual int32_t count(UErrorCode& status) const = 0;
100
101    /**
102     * <p>Returns the next element as a NUL-terminated char*.  If there
103     * are no more elements, returns NULL.  If the resultLength pointer
104     * is not NULL, the length of the string (not counting the
105     * terminating NUL) is returned at that address.  If an error
106     * status is returned, the value at resultLength is undefined.</p>
107     *
108     * <p>The returned pointer is owned by this iterator and must not be
109     * deleted by the caller.  The pointer is valid until the next call
110     * to next, unext, snext, reset, or the enumerator's destructor.</p>
111     *
112     * <p>If the iterator is out of sync with its service, status is set
113     * to U_ENUM_OUT_OF_SYNC_ERROR and NULL is returned.</p>
114     *
115     * <p>If the native service string is a char16_t* string, it is
116     * converted to char* with the invariant converter.  If the
117     * conversion fails (because a character cannot be converted) then
118     * status is set to U_INVARIANT_CONVERSION_ERROR and the return
119     * value is undefined (though not NULL).</p>
120     *
121     * Starting with ICU 2.8, the default implementation calls snext()
122     * and handles the conversion.
123     * Either next() or snext() must be implemented differently by a subclass.
124     *
125     * @param status the error code.
126     * @param resultLength a pointer to receive the length, can be NULL.
127     * @return a pointer to the string, or NULL.
128     *
129     * @stable ICU 2.4
130     */
131    virtual const char* next(int32_t *resultLength, UErrorCode& status);
132
133    /**
134     * <p>Returns the next element as a NUL-terminated char16_t*.  If there
135     * are no more elements, returns NULL.  If the resultLength pointer
136     * is not NULL, the length of the string (not counting the
137     * terminating NUL) is returned at that address.  If an error
138     * status is returned, the value at resultLength is undefined.</p>
139     *
140     * <p>The returned pointer is owned by this iterator and must not be
141     * deleted by the caller.  The pointer is valid until the next call
142     * to next, unext, snext, reset, or the enumerator's destructor.</p>
143     *
144     * <p>If the iterator is out of sync with its service, status is set
145     * to U_ENUM_OUT_OF_SYNC_ERROR and NULL is returned.</p>
146     *
147     * Starting with ICU 2.8, the default implementation calls snext()
148     * and handles the conversion.
149     *
150     * @param status the error code.
151     * @param resultLength a ponter to receive the length, can be NULL.
152     * @return a pointer to the string, or NULL.
153     *
154     * @stable ICU 2.4
155     */
156    virtual const char16_t* unext(int32_t *resultLength, UErrorCode& status);
157
158    /**
159     * <p>Returns the next element a UnicodeString*.  If there are no
160     * more elements, returns NULL.</p>
161     *
162     * <p>The returned pointer is owned by this iterator and must not be
163     * deleted by the caller.  The pointer is valid until the next call
164     * to next, unext, snext, reset, or the enumerator's destructor.</p>
165     *
166     * <p>If the iterator is out of sync with its service, status is set
167     * to U_ENUM_OUT_OF_SYNC_ERROR and NULL is returned.</p>
168     *
169     * Starting with ICU 2.8, the default implementation calls next()
170     * and handles the conversion.
171     * Either next() or snext() must be implemented differently by a subclass.
172     *
173     * @param status the error code.
174     * @return a pointer to the string, or NULL.
175     *
176     * @stable ICU 2.4
177     */
178    virtual const UnicodeString* snext(UErrorCode& status);
179
180    /**
181     * <p>Resets the iterator.  This re-establishes sync with the
182     * service and rewinds the iterator to start at the first
183     * element.</p>
184     *
185     * <p>Previous pointers returned by next, unext, or snext become
186     * invalid, and the value returned by count might change.</p>
187     *
188     * @param status the error code.
189     *
190     * @stable ICU 2.4
191     */
192    virtual void reset(UErrorCode& status) = 0;
193
194    /**
195     * Compares this enumeration to other to check if both are equal
196     *
197     * @param that The other string enumeration to compare this object to
198     * @return TRUE if the enumerations are equal. FALSE if not.
199     * @stable ICU 3.6
200     */
201    virtual UBool operator==(const StringEnumeration& that)const;
202    /**
203     * Compares this enumeration to other to check if both are not equal
204     *
205     * @param that The other string enumeration to compare this object to
206     * @return TRUE if the enumerations are equal. FALSE if not.
207     * @stable ICU 3.6
208     */
209    virtual UBool operator!=(const StringEnumeration& that)const;
210
211protected:
212    /**
213     * UnicodeString field for use with default implementations and subclasses.
214     * @stable ICU 2.8
215     */
216    UnicodeString unistr;
217    /**
218     * char * default buffer for use with default implementations and subclasses.
219     * @stable ICU 2.8
220     */
221    char charsBuffer[32];
222    /**
223     * char * buffer for use with default implementations and subclasses.
224     * Allocated in constructor and in ensureCharsCapacity().
225     * @stable ICU 2.8
226     */
227    char *chars;
228    /**
229     * Capacity of chars, for use with default implementations and subclasses.
230     * @stable ICU 2.8
231     */
232    int32_t charsCapacity;
233
234    /**
235     * Default constructor for use with default implementations and subclasses.
236     * @stable ICU 2.8
237     */
238    StringEnumeration();
239
240    /**
241     * Ensures that chars is at least as large as the requested capacity.
242     * For use with default implementations and subclasses.
243     *
244     * @param capacity Requested capacity.
245     * @param status ICU in/out error code.
246     * @stable ICU 2.8
247     */
248    void ensureCharsCapacity(int32_t capacity, UErrorCode &status);
249
250    /**
251     * Converts s to Unicode and sets unistr to the result.
252     * For use with default implementations and subclasses,
253     * especially for implementations of snext() in terms of next().
254     * This is provided with a helper function instead of a default implementation
255     * of snext() to avoid potential infinite loops between next() and snext().
256     *
257     * For example:
258     * \code
259     * const UnicodeString* snext(UErrorCode& status) {
260     *   int32_t resultLength=0;
261     *   const char *s=next(&resultLength, status);
262     *   return setChars(s, resultLength, status);
263     * }
264     * \endcode
265     *
266     * @param s String to be converted to Unicode.
267     * @param length Length of the string.
268     * @param status ICU in/out error code.
269     * @return A pointer to unistr.
270     * @stable ICU 2.8
271     */
272    UnicodeString *setChars(const char *s, int32_t length, UErrorCode &status);
273};
274
275U_NAMESPACE_END
276
277/* STRENUM_H */
278#endif
279