icuSources/common/unistrappender.h

   1 // © 2016 and later: Unicode, Inc. and others.
   2 // License & terms of use: http://www.unicode.org/copyright.html
   3 /*
   4 ******************************************************************************
   5 * Copyright (C) 2015, International Business Machines Corporation and
   6 * others. All Rights Reserved.
   7 ******************************************************************************
   8 *
   9 * File unistrappender.h
  10 ******************************************************************************
  11 */
  12
  13 #ifndef __UNISTRAPPENDER_H__
  14 #define __UNISTRAPPENDER_H__
  15
  16 #include "unicode/unistr.h"
  17 #include "unicode/uobject.h"
  18 #include "unicode/utf16.h"
  19 #include "unicode/utypes.h"
  20 #include "cmemory.h"
  21
  22 U_NAMESPACE_BEGIN
  23
  24 /**
  25  * An optimization for the slowness of calling UnicodeString::append()
  26  * one character at a time in a loop. It stores appends in a buffer while
  27  * never actually calling append on the unicode string unless the buffer
  28  * fills up or is flushed.
  29  *
  30  * proper usage:
  31  * {
  32  *     UnicodeStringAppender appender(astring);
  33  *     for (int32_t i = 0; i < 100; ++i) {
  34  *        appender.append((UChar) i);
  35  *     }
  36  *     // appender flushed automatically when it goes out of scope.
  37  * }
  38  */
  39 class UnicodeStringAppender : public UMemory {
  40 public:
  41
  42     /**
  43      * dest is the UnicodeString being appended to. It must always
  44      * exist while this instance exists.
  45      */
  46     UnicodeStringAppender(UnicodeString &dest) : fDest(&dest), fIdx(0) { }
  47
  48     inline void append(UChar x) {
  49         if (fIdx == UPRV_LENGTHOF(fBuffer)) {
  50             fDest->append(fBuffer, 0, fIdx);
  51             fIdx = 0;
  52         }
  53         fBuffer[fIdx++] = x;
  54     }
  55
  56     inline void append(UChar32 x) {
  57         if (fIdx >= UPRV_LENGTHOF(fBuffer) - 1) {
  58             fDest->append(fBuffer, 0, fIdx);
  59             fIdx = 0;
  60         }
  61         U16_APPEND_UNSAFE(fBuffer, fIdx, x);
  62     }
  63
  64     /**
  65      * Ensures that all appended characters have been written out to dest.
  66      */
  67     inline void flush() {
  68         if (fIdx) {
  69             fDest->append(fBuffer, 0, fIdx);
  70         }
  71         fIdx = 0;
  72     }
  73
  74     /**
  75      * flush the buffer when we go out of scope.
  76      */
  77     ~UnicodeStringAppender() {
  78         flush();
  79     }
  80 private:
  81     UnicodeString *fDest;
  82     int32_t fIdx;
  83     UChar fBuffer[32];
  84     UnicodeStringAppender(const UnicodeStringAppender &other);
  85     UnicodeStringAppender &operator=(const UnicodeStringAppender &other);
  86 };
  87
  88 U_NAMESPACE_END
  89
  90 #endif