/*

*******************************************************************************

*

*   Copyright (C) 2002-2005, International Business Machines

*   Corporation and others.  All Rights Reserved.

*

*******************************************************************************

*/

#ifndef STRENUM_H

#define STRENUM_H

#include "unicode/uobject.h"

#include "unicode/unistr.h"

/**

 * \file 

 * \brief C++ API: String Enumeration

 */

U_NAMESPACE_BEGIN

/**

 * Base class for 'pure' C++ implementations of uenum api.  Adds a

 * method that returns the next UnicodeString since in C++ this can

 * be a common storage format for strings.

 *

 * <p>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.</p>

 *

 * <p>Strings may take the form of const char*, const UChar*, 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.</p>

 *

 * <p>The pointers returned by next, unext, and snext become invalid

 * upon any subsequent call to the enumeration's destructor, next,

 * unext, snext, or reset.</p>

 *

 * 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 clone functions in all subclasses return a base class pointer

     * because some compilers do not support covariant (same-as-this)

     * return types; cast to the appropriate subclass if necessary.

     * The caller must delete the clone.

     *

     * @return a clone of this object

     *

     * @see getDynamicClassID

     * @stable ICU 2.8

     */

    virtual StringEnumeration *clone() const;

    /**

     * <p>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.</p>

     *

     * <p>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.</p>

     *

     * <p>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).</p>

     *

     * @param status the error code.

     * @return number of elements in the iterator.

     *

     * @stable ICU 2.4 */

    virtual int32_t count(UErrorCode& status) const = 0;

    /**

     * <p>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.</p>

     *

     * <p>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 destructor.</p>

     *

     * <p>If the iterator is out of sync with its service, status is set

     * to U_ENUM_OUT_OF_SYNC_ERROR and NULL is returned.</p>

     *

     * <p>If the native service string is a UChar* string, it is

     * converted to char* with the invariant converter.  If the

     * conversion fails (because a character cannot be converted) then

     * status is set to U_INVARIANT_CONVERSION_ERROR and the return

     * value is undefined (though not NULL).</p>

     *

     * Starting with ICU 2.8, the default implementation calls snext()

     * and handles the conversion.

     *

     * @param status the error code.

     * @param resultLength a pointer to receive the length, can be NULL.

     * @return a pointer to the string, or NULL.

     *

     * @stable ICU 2.4 

     */

    virtual const char* next(int32_t *resultLength, UErrorCode& status);

    /**

     * <p>Returns the next element as a NUL-terminated UChar*.  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.</p>

     *

     * <p>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 destructor.</p>

     *

     * <p>If the iterator is out of sync with its service, status is set

     * to U_ENUM_OUT_OF_SYNC_ERROR and NULL is returned.</p>

     *

     * Starting with ICU 2.8, the default implementation calls snext()

     * and handles the conversion.

     *

     * @param status the error code.

     * @param resultLength a ponter to receive the length, can be NULL.

     * @return a pointer to the string, or NULL.

     *

     * @stable ICU 2.4 

     */

    virtual const UChar* unext(int32_t *resultLength, UErrorCode& status);

    /**

     * <p>Returns the next element a UnicodeString*.  If there are no

     * more elements, returns NULL.</p>

     *

     * <p>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 destructor.</p>

     *

     * <p>If the iterator is out of sync with its service, status is set

     * to U_ENUM_OUT_OF_SYNC_ERROR and NULL is returned.</p>

     *

     * @param status the error code.

     * @return a pointer to the string, or NULL.

     *

     * @stable ICU 2.4 

     */

    virtual const UnicodeString* snext(UErrorCode& status) = 0;

    /**

     * <p>Resets the iterator.  This re-establishes sync with the

     * service and rewinds the iterator to start at the first

     * element.</p>

     *

     * <p>Previous pointers returned by next, unext, or snext become

     * invalid, and the value returned by count might change.</p>

     *

     * @param status the error code.

     *

     * @stable ICU 2.4 

     */

    virtual void reset(UErrorCode& status) = 0;

protected:

    /**

     * UnicodeString field for use with default implementations and subclasses.

     * @stable ICU 2.8

     */

    UnicodeString unistr;

    /**

     * char * default buffer for use with default implementations and subclasses.

     * @stable ICU 2.8

     */

    char charsBuffer[32];

    /**

     * char * buffer for use with default implementations and subclasses.

     * Allocated in constructor and in ensureCharsCapacity().

     * @stable ICU 2.8

     */

    char *chars;

    /**

     * Capacity of chars, for use with default implementations and subclasses.

     * @stable ICU 2.8

     */

    int32_t charsCapacity;

    /**

     * Default constructor for use with default implementations and subclasses.

     * @stable ICU 2.8

     */

    StringEnumeration();

    /**

     * Ensures that chars is at least as large as the requested capacity.

     * For use with default implementations and subclasses.

     *

     * @param capacity Requested capacity.

     * @param status ICU in/out error code.

     * @stable ICU 2.8

     */

    void ensureCharsCapacity(int32_t capacity, UErrorCode &status);

    /**

     * Converts s to Unicode and sets unistr to the result.

     * For use with default implementations and subclasses,

     * especially for implementations of snext() in terms of next().

     * This is provided with a helper function instead of a default implementation

     * of snext() to avoid potential infinite loops between next() and snext().

     *

     * For example:

     * \code

     * const UnicodeString* snext(UErrorCode& status) {

     *   int32_t resultLength=0;

     *   const char *s=next(&resultLength, status);

     *   return setChars(s, resultLength, status);

     * }

     * \endcode

     *

     * @param s String to be converted to Unicode.

     * @param length Length of the string.

     * @param status ICU in/out error code.

     * @return A pointer to unistr.

     * @stable ICU 2.8

     */

    UnicodeString *setChars(const char *s, int32_t length, UErrorCode &status);

};

U_NAMESPACE_END

/* STRENUM_H */

#endif