icuSources/common/unicode/strenum.h

   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
  21 U_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  */
  55 class U_COMMON_API StringEnumeration : public UObject {
  56 public:
  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
 209 protected:
 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
 273 U_NAMESPACE_END
 274
 275 /* STRENUM_H */
 276 #endif