stringからUTF-8符号化をUnicode code pointに復号する

前回UTF-8コード実測でboost.localeライブラリは、1文字のUTF-8符号化をUnicode code pointに変換する.
今日localeのコードの一部を見て、作者Artyomはutf_を使うことを提案しますto_utf関数はすべてを解決します.私のニーズはstringのすべての文字列のunicode code pointを解析することです.utf_のようです.to_utf名は適切ではありません.
そこでArtyomのコードの一部を修正し、まずmainを見てみましょう.ccの呼び出しコード:

#include "test.h"
#include "util/endian.h"
#include "util/utf.h"
#include <iostream>

using namespace std;

int main(int argc, char ** argv) {
  // TEST(3 > 2);
  char const * p = " ";
  cout << PrintStringAsBinaryString(p) << endl;
  string str = " ";
  cout << PrintStringAsBinaryString(str) << endl;

  string::iterator itor = str.begin();
  vector<code_point> points;
  UTF8ToUnicode(itor, str.end(), points);
  cout << "code point0: 0x" << std::hex << points[0] << " binary format:B" << PrintIntAsBinaryString(points[0]) << endl;
  cout << "code point1: 0x" << std::hex << points[1] << " binary format:B" << PrintIntAsBinaryString(points[1]) << endl;
  cout << "code point2: 0x" << std::hex << points[2] << " binary format:B" << PrintIntAsBinaryString(points[2]) << endl;
}

実行結果文字列「一二三」は、次のように印刷される.

code point0: 0x4e00 binary format:B00000000000000000100111000000000
code point1: 0x4e8c binary format:B00000000000000000100111010001100
code point2: 0x4e09 binary format:B00000000000000000100111000001001

すべての実装コードはutf.h中:

#ifndef UTIL_UTF_H_
#define UTIL_UTF_H_

#include "util/endian.h"
#include "util/unicode_error.h"
#include <boost/locale/utf.hpp>

using namespace boost::locale::utf;

string PrintStringAsBinaryString(char const* p) {
  stringstream stream;
  for (size_t i = 0; i < strlen(p); ++i) {
    stream << PrintIntAsBinaryString(p[i]);
    stream << " ";
  }
  return stream.str();
}

string PrintStringAsBinaryString(string const& str) {
  stringstream stream;
  for (size_t i = 0; i < str.size(); ++i) {
    stream << PrintIntAsBinaryString(str[i]);
    stream << " ";
  }
  return stream.str();
}



struct ParseResult {
  code_point point;
  size_t size;
};

int trail_length(char ci) {
  unsigned char c = ci;
  if(c < 128)
    return 0;
  if(BOOST_LOCALE_UNLIKELY(c < 194))
    return -1;
  if(c < 224)
    return 1;
  if(c < 240)
    return 2;
  if(BOOST_LOCALE_LIKELY(c <=244))
    return 3;
  return -1;
}

int width(code_point value) {
  if(value <=0x7F) {
    return 1;
  }
  else if(value <=0x7FF) {
    return 2;
  }
  else if(BOOST_LOCALE_LIKELY(value <=0xFFFF)) {
    return 3;
  }
  else {
    return 4;
  }
}

bool is_trail(char ci) {
  unsigned char c = ci;
  return (c & 0xC0) == 0x80;
}

bool is_lead(char ci) {
  return !is_trail(ci);
}

// Convert the UTF-8 string into 
template<typename Iterator>
void ParseUTF8(Iterator &p, Iterator e, ParseResult& result) {
  if (BOOST_LOCALE_UNLIKELY(p == e)) {
    throw UnicodeError("ParseUTF8 failed");
  }

  unsigned char lead = *p++;

  // First byte is fully validated here
  int trail_size = trail_length(lead);

  if(BOOST_LOCALE_UNLIKELY(trail_size < 0)) {
    throw UnicodeError("ParseUTF8 failed");
  }

  //
  // Ok as only ASCII may be of size = 0
  // also optimize for ASCII text
  //
  if(trail_size == 0) {
    result.point = lead;
    result.size = 1;
    return;
  }
            
  code_point c = lead & ((1<<(6-trail_size))-1);

  // Read the rest
  unsigned char tmp;
  switch(trail_size) {
  case 3:
    if(BOOST_LOCALE_UNLIKELY(p==e)) {
      throw UnicodeError("ParseUTF8 failed");
    }
    tmp = *p++;
    c = (c << 6) | ( tmp & 0x3F);
  case 2:
    if(BOOST_LOCALE_UNLIKELY(p==e)) {
      throw UnicodeError("ParseUTF8 failed");
    }
    tmp = *p++;
    c = (c << 6) | ( tmp & 0x3F);
  case 1:
    if(BOOST_LOCALE_UNLIKELY(p==e)) {
      throw UnicodeError("ParseUTF8 failed");
    }
    tmp = *p++;
    c = (c << 6) | ( tmp & 0x3F);
  }

  // Check code point validity: no surrogates and
  // valid range
  if(BOOST_LOCALE_UNLIKELY(!is_valid_codepoint(c))) {
    throw UnicodeError("ParseUTF8 failed");
  }

  // make sure it is the most compact representation
  if(BOOST_LOCALE_UNLIKELY(width(c) != trail_size + 1)) {
    throw UnicodeError("ParseUTF8 failed");
  }
  
  result.point = c;
  result.size = trail_size + 1;
}

// Convert the UTF-8 string that represent one single Unicode character in [start, end) to Unicode code point
template<typename Iterator>
code_point UTF8ToUnicode(Iterator &start, Iterator end) {
  ParseResult result;
  ParseUTF8(start, end, result);
  return result.point;
}

template<typename Iterator>
code_point UTF8ToUnicode(Iterator &start, Iterator end, vector<code_point>& points) {
  ParseResult result;
  Iterator begin = start;
  while (begin < end) {
    ParseUTF8(start, end, result);
    points.push_back(result.point);
    begin += result.size;
  }
}


#endif

wstring私は研究したことがありません.しかし一般的にstringは私にとって十分で、UnicodeとUTF-8の符号化を理解した後、システムに対する理解は大きく向上しました.