icuSources/common/unicode/strenum.h

   1 /*
   2 *******************************************************************************
   3 *
   4 *   Copyright (C) 2002-2004, 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 U_NAMESPACE_BEGIN
  17
  18 /**
  19  * Base class for 'pure' C++ implementations of uenum api.  Adds a
  20  * method that returns the next UnicodeString since in C++ this can
  21  * be a common storage format for strings.
  22  *
  23  * <p>The model is that the enumeration is over strings maintained by
  24  * a 'service.'  At any point, the service might change, invalidating
  25  * the enumerator (though this is expected to be rare).  The iterator
  26  * returns an error if this has occurred.  Lack of the error is no
  27  * guarantee that the service didn't change immediately after the
  28  * call, so the returned string still might not be 'valid' on
  29  * subsequent use.</p>
  30  *
  31  * <p>Strings may take the form of const char*, const UChar*, or const
  32  * UnicodeString*.  The type you get is determine by the variant of
  33  * 'next' that you call.  In general the StringEnumeration is
  34  * optimized for one of these types, but all StringEnumerations can
  35  * return all types.  Returned strings are each terminated with a NUL.
  36  * Depending on the service data, they might also include embedded NUL
  37  * characters, so API is provided to optionally return the true
  38  * length, counting the embedded NULs but not counting the terminating
  39  * NUL.</p>
  40  *
  41  * <p>The pointers returned by next, unext, and snext become invalid
  42  * upon any subsequent call to the enumeration's destructor, next,
  43  * unext, snext, or reset.</p>
  44  *
  45  * ICU 2.8 adds some default implementations and helper functions
  46  * for subclasses.
  47  *
  48  * @stable ICU 2.4
  49  */
  50 class U_COMMON_API StringEnumeration : public UObject {
  51 public:
  52     /**
  53      * Destructor.
  54      * @stable ICU 2.4
  55      */
  56     virtual ~StringEnumeration();
  57
  58     /**
  59      * Clone this object, an instance of a subclass of StringEnumeration.
  60      * Clones can be used concurrently in multiple threads.
  61      * If a subclass does not implement clone(), or if an error occurs,
  62      * then NULL is returned.
  63      * The clone functions in all subclasses return a base class pointer
  64      * because some compilers do not support covariant (same-as-this)
  65      * return types; cast to the appropriate subclass if necessary.
  66      * The caller must delete the clone.
  67      *
  68      * @return a clone of this object
  69      *
  70      * @see getDynamicClassID
  71      * @draft ICU 2.8
  72      */
  73     virtual StringEnumeration *clone() const;
  74
  75     /**
  76      * <p>Return the number of elements that the iterator traverses.  If
  77      * the iterator is out of sync with its service, status is set to
  78      * U_ENUM_OUT_OF_SYNC_ERROR, and the return value is zero.</p>
  79      *
  80      * <p>The return value will not change except possibly as a result of
  81      * a subsequent call to reset, or if the iterator becomes out of sync.</p>
  82      *
  83      * <p>This is a convenience function. It can end up being very
  84      * expensive as all the items might have to be pre-fetched
  85      * (depending on the storage format of the data being
  86      * traversed).</p>
  87      *
  88      * @param status the error code.
  89      * @return number of elements in the iterator.
  90      *
  91      * @stable ICU 2.4 */
  92     virtual int32_t count(UErrorCode& status) const = 0;
  93
  94     /**
  95      * <p>Returns the next element as a NUL-terminated char*.  If there
  96      * are no more elements, returns NULL.  If the resultLength pointer
  97      * is not NULL, the length of the string (not counting the
  98      * terminating NUL) is returned at that address.  If an error
  99      * status is returned, the value at resultLength is undefined.</p>
 100      *
 101      * <p>The returned pointer is owned by this iterator and must not be
 102      * deleted by the caller.  The pointer is valid until the next call
 103      * to next, unext, snext, reset, or the enumerator's destructor.</p>
 104      *
 105      * <p>If the iterator is out of sync with its service, status is set
 106      * to U_ENUM_OUT_OF_SYNC_ERROR and NULL is returned.</p>
 107      *
 108      * <p>If the native service string is a UChar* string, it is
 109      * converted to char* with the invariant converter.  If the
 110      * conversion fails (because a character cannot be converted) then
 111      * status is set to U_INVARIANT_CONVERSION_ERROR and the return
 112      * value is undefined (though not NULL).</p>
 113      *
 114      * Starting with ICU 2.8, the default implementation calls snext()
 115      * and handles the conversion.
 116      *
 117      * @param status the error code.
 118      * @param resultLength a pointer to receive the length, can be NULL.
 119      * @return a pointer to the string, or NULL.
 120      *
 121      * @stable ICU 2.4
 122      */
 123     virtual const char* next(int32_t *resultLength, UErrorCode& status);
 124
 125     /**
 126      * <p>Returns the next element as a NUL-terminated UChar*.  If there
 127      * are no more elements, returns NULL.  If the resultLength pointer
 128      * is not NULL, the length of the string (not counting the
 129      * terminating NUL) is returned at that address.  If an error
 130      * status is returned, the value at resultLength is undefined.</p>
 131      *
 132      * <p>The returned pointer is owned by this iterator and must not be
 133      * deleted by the caller.  The pointer is valid until the next call
 134      * to next, unext, snext, reset, or the enumerator's destructor.</p>
 135      *
 136      * <p>If the iterator is out of sync with its service, status is set
 137      * to U_ENUM_OUT_OF_SYNC_ERROR and NULL is returned.</p>
 138      *
 139      * Starting with ICU 2.8, the default implementation calls snext()
 140      * and handles the conversion.
 141      *
 142      * @param status the error code.
 143      * @param resultLength a ponter to receive the length, can be NULL.
 144      * @return a pointer to the string, or NULL.
 145      *
 146      * @stable ICU 2.4
 147      */
 148     virtual const UChar* unext(int32_t *resultLength, UErrorCode& status);
 149
 150     /**
 151      * <p>Returns the next element a UnicodeString*.  If there are no
 152      * more elements, returns NULL.</p>
 153      *
 154      * <p>The returned pointer is owned by this iterator and must not be
 155      * deleted by the caller.  The pointer is valid until the next call
 156      * to next, unext, snext, reset, or the enumerator's destructor.</p>
 157      *
 158      * <p>If the iterator is out of sync with its service, status is set
 159      * to U_ENUM_OUT_OF_SYNC_ERROR and NULL is returned.</p>
 160      *
 161      * @param status the error code.
 162      * @return a pointer to the string, or NULL.
 163      *
 164      * @stable ICU 2.4
 165      */
 166     virtual const UnicodeString* snext(UErrorCode& status) = 0;
 167
 168     /**
 169      * <p>Resets the iterator.  This re-establishes sync with the
 170      * service and rewinds the iterator to start at the first
 171      * element.</p>
 172      *
 173      * <p>Previous pointers returned by next, unext, or snext become
 174      * invalid, and the value returned by count might change.</p>
 175      *
 176      * @param status the error code.
 177      *
 178      * @stable ICU 2.4
 179      */
 180     virtual void reset(UErrorCode& status) = 0;
 181
 182 protected:
 183     /**
 184      * UnicodeString field for use with default implementations and subclasses.
 185      * @draft ICU 2.8
 186      */
 187     UnicodeString unistr;
 188     /**
 189      * char * default buffer for use with default implementations and subclasses.
 190      * @draft ICU 2.8
 191      */
 192     char charsBuffer[32];
 193     /**
 194      * char * buffer for use with default implementations and subclasses.
 195      * Allocated in constructor and in ensureCharsCapacity().
 196      * @draft ICU 2.8
 197      */
 198     char *chars;
 199     /**
 200      * Capacity of chars, for use with default implementations and subclasses.
 201      * @draft ICU 2.8
 202      */
 203     int32_t charsCapacity;
 204
 205     /**
 206      * Default constructor for use with default implementations and subclasses.
 207      * @draft ICU 2.8
 208      */
 209     StringEnumeration();
 210
 211     /**
 212      * Ensures that chars is at least as large as the requested capacity.
 213      * For use with default implementations and subclasses.
 214      *
 215      * @param capacity Requested capacity.
 216      * @param status ICU in/out error code.
 217      * @draft ICU 2.8
 218      */
 219     void ensureCharsCapacity(int32_t capacity, UErrorCode &status);
 220
 221     /**
 222      * Converts s to Unicode and sets unistr to the result.
 223      * For use with default implementations and subclasses,
 224      * especially for implementations of snext() in terms of next().
 225      * This is provided with a helper function instead of a default implementation
 226      * of snext() to avoid potential infinite loops between next() and snext().
 227      *
 228      * For example:
 229      * \code
 230      * const UnicodeString* snext(UErrorCode& status) {
 231      *   int32_t resultLength=0;
 232      *   const char *s=next(&resultLength, status);
 233      *   return setChars(s, resultLength, status);
 234      * }
 235      * \endcode
 236      *
 237      * @param s String to be converted to Unicode.
 238      * @param length Length of the string.
 239      * @param status ICU in/out error code.
 240      * @return A pointer to unistr.
 241      * @draft ICU 2.8
 242      */
 243     UnicodeString *setChars(const char *s, int32_t length, UErrorCode &status);
 244 };
 245
 246 U_NAMESPACE_END
 247
 248 /* STRENUM_H */
 249 #endif