C++에서 StringBuilder 류 의 실현 과 성능 최적화

#include <iostream>// for std::cout, std::endl
#include <string> // for std::string
#include <vector> // for std::vector
#include <numeric> // for std::accumulate
int main()
{
  using namespace std;
  vector<string> vec = { "hello", " ", "world" };
  string s = accumulate(vec.begin(), vec.end(), s);
  cout << s << endl; // prints 'hello world' to standard output.
  return 0;
}

// Subset of http://msdn.microsoft.com/en-us/library/system.text.stringbuilder.aspx
template <typename chr>
class StringBuilder {
  typedef std::basic_string<chr> string_t;
  typedef std::list<string_t> container_t; // Reasons not to use vector below.
  typedef typename string_t::size_type size_type; // Reuse the size type in the string.
  container_t m_Data;
  size_type m_totalSize;
  void append(const string_t &src) {
    m_Data.push_back(src);
    m_totalSize += src.size();
  }
  // No copy constructor, no assignement.
  StringBuilder(const StringBuilder &);
  StringBuilder & operator = (const StringBuilder &);
public:
  StringBuilder(const string_t &src) {
    if (!src.empty()) {
      m_Data.push_back(src);
    }
    m_totalSize = src.size();
  }
  StringBuilder() {
    m_totalSize = 0;
  }
  // TODO: Constructor that takes an array of strings.
 
 
  StringBuilder & Append(const string_t &src) {
    append(src);
    return *this; // allow chaining.
  }
    // This one lets you add any STL container to the string builder.
  template<class inputIterator>
  StringBuilder & Add(const inputIterator &first, const inputIterator &afterLast) {
    // std::for_each and a lambda look like overkill here.
        // <b>Not</b> using std::copy, since we want to update m_totalSize too.
    for (inputIterator f = first; f != afterLast; ++f) {
      append(*f);
    }
    return *this; // allow chaining.
  }
  StringBuilder & AppendLine(const string_t &src) {
    static chr lineFeed[] { 10, 0 }; // C++ 11. Feel the love!
    m_Data.push_back(src + lineFeed);
    m_totalSize += 1 + src.size();
    return *this; // allow chaining.
  }
  StringBuilder & AppendLine() {
    static chr lineFeed[] { 10, 0 };
    m_Data.push_back(lineFeed);
    ++m_totalSize;
    return *this; // allow chaining.
  }
 
  // TODO: AppendFormat implementation. Not relevant for the article.
 
  // Like C# StringBuilder.ToString()
  // Note the use of reserve() to avoid reallocations.
  string_t ToString() const {
    string_t result;
    // The whole point of the exercise!
    // If the container has a lot of strings, reallocation (each time the result grows) will take a serious toll,
    // both in performance and chances of failure.
    // I measured (in code I cannot publish) fractions of a second using 'reserve', and almost two minutes using +=.
    result.reserve(m_totalSize + 1);
  // result = std::accumulate(m_Data.begin(), m_Data.end(), result); // This would lose the advantage of 'reserve'
    for (auto iter = m_Data.begin(); iter != m_Data.end(); ++iter) {
      result += *iter;
    }
    return result;
  }
 
  // like javascript Array.join()
  string_t Join(const string_t &delim) const {
    if (delim.empty()) {
      return ToString();
    }
    string_t result;
    if (m_Data.empty()) {
      return result;
    }
    // Hope we don't overflow the size type.
    size_type st = (delim.size() * (m_Data.size() - 1)) + m_totalSize + 1;
    result.reserve(st);
        // If you need reasons to love C++11, here is one.
    struct adder {
      string_t m_Joiner;
      adder(const string_t &s): m_Joiner(s) {
        // This constructor is NOT empty.
      }
            // This functor runs under accumulate() without reallocations, if 'l' has reserved enough memory.
      string_t operator()(string_t &l, const string_t &r) {
        l += m_Joiner;
        l += r;
        return l;
      }
    } adr(delim);
    auto iter = m_Data.begin();
        // Skip the delimiter before the first element in the container.
    result += *iter;
    return std::accumulate(++iter, m_Data.end(), result, adr);
  }
 
}; // class StringBuilder

void TestPerformance(const StringBuilder<wchar_t> &tested, const std::vector<std::wstring> &tested2) {
  const int loops = 500;
  clock_t start = clock(); // Give up some accuracy in exchange for platform independence.
  for (int i = 0; i < loops; ++i) {
    std::wstring accumulator;
    std::accumulate(tested2.begin(), tested2.end(), accumulator);
  }
  double secsAccumulate = (double) (clock() - start) / CLOCKS_PER_SEC;
 
  start = clock();
  for (int i = 0; i < loops; ++i) {
    std::wstring result2 = tested.ToString();
  }
  double secsBuilder = (double) (clock() - start) / CLOCKS_PER_SEC;
  using std::cout;
  using std::endl;
  cout << "Accumulate took " << secsAccumulate << " seconds, and ToString() took " << secsBuilder << " seconds."
      << " The relative speed improvement was " << ((secsAccumulate / secsBuilder) - 1) * 100 << "%"
      << endl;
}

#ifdef __USE_POSIX199309
 
// Thanks to <a href="http://www.guyrutenberg.com/2007/09/22/profiling-code-using-clock_gettime/">Guy Rutenberg</a>.
timespec diff(timespec start, timespec end)
{
  timespec temp;
  if ((end.tv_nsec-start.tv_nsec)<0) {
    temp.tv_sec = end.tv_sec-start.tv_sec-1;
    temp.tv_nsec = 1000000000+end.tv_nsec-start.tv_nsec;
  } else {
    temp.tv_sec = end.tv_sec-start.tv_sec;
    temp.tv_nsec = end.tv_nsec-start.tv_nsec;
  }
  return temp;
}
 
void AccurateTestPerformance(const StringBuilder<wchar_t> &tested, const std::vector<std::wstring> &tested2) {
  const int loops = 500;
  timespec time1, time2;
  // Don't forget to add -lrt to the g++ linker command line.
  ////////////////
  // Test std::accumulate()
  ////////////////
  clock_gettime(CLOCK_THREAD_CPUTIME_ID, &time1);
  for (int i = 0; i < loops; ++i) {
    std::wstring accumulator;
    std::accumulate(tested2.begin(), tested2.end(), accumulator);
  }
  clock_gettime(CLOCK_THREAD_CPUTIME_ID, &time2);
  using std::cout;
  using std::endl;
  timespec tsAccumulate =diff(time1,time2);
  cout << tsAccumulate.tv_sec << ":" << tsAccumulate.tv_nsec << endl;
  ////////////////
  // Test ToString()
  ////////////////
  clock_gettime(CLOCK_THREAD_CPUTIME_ID, &time1);
  for (int i = 0; i < loops; ++i) {
    std::wstring result2 = tested.ToString();
  }
  clock_gettime(CLOCK_THREAD_CPUTIME_ID, &time2);
  timespec tsToString =diff(time1,time2);
  cout << tsToString.tv_sec << ":" << tsToString.tv_nsec << endl;
  ////////////////
  // Test join()
  ////////////////
  clock_gettime(CLOCK_THREAD_CPUTIME_ID, &time1);
  for (int i = 0; i < loops; ++i) {
    std::wstring result3 = tested.Join(L",");
  }
  clock_gettime(CLOCK_THREAD_CPUTIME_ID, &time2);
  timespec tsJoin =diff(time1,time2);
  cout << tsJoin.tv_sec << ":" << tsJoin.tv_nsec << endl;
 
  ////////////////
  // Show results
  ////////////////
  double secsAccumulate = tsAccumulate.tv_sec + tsAccumulate.tv_nsec / 1000000000.0;
  double secsBuilder = tsToString.tv_sec + tsToString.tv_nsec / 1000000000.0;
    double secsJoin = tsJoin.tv_sec + tsJoin.tv_nsec / 1000000000.0;
  cout << "Accurate performance test:" << endl << "  Accumulate took " << secsAccumulate << " seconds, and ToString() took " << secsBuilder << " seconds." << endl
      << "  The relative speed improvement was " << ((secsAccumulate / secsBuilder) - 1) * 100 << "%" << endl <<
       "   Join took " << secsJoin << " seconds."
      << endl;
}
#endif // def __USE_POSIX199309

int main() {
  ////////////////////////////////////
  // 8-bit characters (ANSI)
  ////////////////////////////////////
  StringBuilder<char> ansi;
  ansi.Append("Hello").Append(" ").AppendLine("World");
  std::cout << ansi.ToString();
 
  ////////////////////////////////////
  // Wide characters (Unicode)
  ////////////////////////////////////
  // http://en.wikipedia.org/wiki/Cargo_cult
  std::vector<std::wstring> cargoCult
  {
    L"A", L" cargo", L" cult", L" is", L" a", L" kind", L" of", L" Melanesian", L" millenarian", L" movement",
// many more lines here...
L" applied", L" retroactively", L" to", L" movements", L" in", L" a", L" much", L" earlier", L" era.
"
  };
  StringBuilder<wchar_t> wide;
  wide.Add(cargoCult.begin(), cargoCult.end()).AppendLine();
    // use ToString(), just like .net
  std::wcout << wide.ToString() << std::endl;
  // javascript-like join.
  std::wcout << wide.Join(L" _
") << std::endl;
 
  ////////////////////////////////////
  // Performance tests
  ////////////////////////////////////
  TestPerformance(wide, cargoCult);
#ifdef __USE_POSIX199309
  AccurateTestPerformance(wide, cargoCult);
#endif // def __USE_POSIX199309
  return 0;
}