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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      */
UnicodeStringAppender(UnicodeString & dest)46     UnicodeStringAppender(UnicodeString &dest) : fDest(&dest), fIdx(0) { }
47 
append(UChar x)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 
append(UChar32 x)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      */
flush()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      */
~UnicodeStringAppender()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
91