icuSources/common/unistrappender.h

   1 /*
   2 ******************************************************************************
   3 * Copyright (C) 2015, International Business Machines Corporation and
   4 * others. All Rights Reserved.
   5 ******************************************************************************
   6 *
   7 * File unistrappender.h
   8 ******************************************************************************
   9 */
  10
  11 #ifndef __UNISTRAPPENDER_H__
  12 #define __UNISTRAPPENDER_H__
  13
  14 #include "unicode/unistr.h"
  15 #include "unicode/uobject.h"
  16 #include "unicode/utf16.h"
  17 #include "unicode/utypes.h"
  18 #include "cmemory.h"
  19
  20 U_NAMESPACE_BEGIN
  21
  22 /**
  23  * An optimization for the slowness of calling UnicodeString::append()
  24  * one character at a time in a loop. It stores appends in a buffer while
  25  * never actually calling append on the unicode string unless the buffer
  26  * fills up or is flushed.
  27  *
  28  * proper usage:
  29  * {
  30  *     UnicodeStringAppender appender(astring);
  31  *     for (int32_t i = 0; i < 100; ++i) {
  32  *        appender.append((UChar) i);
  33  *     }
  34  *     // appender flushed automatically when it goes out of scope.
  35  * }
  36  */
  37 class UnicodeStringAppender : public UMemory {
  38 public:
  39
  40     /**
  41      * dest is the UnicodeString being appended to. It must always
  42      * exist while this instance exists.
  43      */
  44     UnicodeStringAppender(UnicodeString &dest) : fDest(&dest), fIdx(0) { }
  45
  46     inline void append(UChar x) {
  47         if (fIdx == UPRV_LENGTHOF(fBuffer)) {
  48             fDest->append(fBuffer, 0, fIdx);
  49             fIdx = 0;
  50         }
  51         fBuffer[fIdx++] = x;
  52     }
  53
  54     inline void append(UChar32 x) {
  55         if (fIdx >= UPRV_LENGTHOF(fBuffer) - 1) {
  56             fDest->append(fBuffer, 0, fIdx);
  57             fIdx = 0;
  58         }
  59         U16_APPEND_UNSAFE(fBuffer, fIdx, x);
  60     }
  61
  62     /**
  63      * Ensures that all appended characters have been written out to dest.
  64      */
  65     inline void flush() {
  66         if (fIdx) {
  67             fDest->append(fBuffer, 0, fIdx);
  68         }
  69         fIdx = 0;
  70     }
  71
  72     /**
  73      * flush the buffer when we go out of scope.
  74      */
  75     ~UnicodeStringAppender() {
  76         flush();
  77     }
  78 private:
  79     UnicodeString *fDest;
  80     int32_t fIdx;
  81     UChar fBuffer[32];
  82     UnicodeStringAppender(const UnicodeStringAppender &other);
  83     UnicodeStringAppender &operator=(const UnicodeStringAppender &other);
  84 };
  85
  86 U_NAMESPACE_END
  87
  88 #endif