c++ - 需要std::vector优化

我编写了一个例程，该例程大量使用std::vector<double>。它运行相当缓慢，并且AQTime似乎暗示我正在构建大量的向量，但不确定为什么会这样。在某些情况下，我的示例运行迭代10次。每次迭代将3个c点数组（约400个点）复制到向量中，并创建3个相同大小的向量以进行输出。每个输出点可能是两个输入向量中最多20个点相加的结果，最坏的情况是10 * 400 * 3 * 2 * 20 = 480,000个引用。令人难以置信的是，探查器指示某些std ::方法被调用了4,600万次。我怀疑我做错了！

一些代码：

vector<double>gdbChannel::GetVector() {
   if (fHaveDoubleData & (fLength > 0)) {
      double * pD = getDoublePointer();
      vector<double>v(pD, pD + fLength);

      return v;
   } else {
      throw(Exception("attempt to retrieve vector on empty line")); ;
   }
}

void gdbChannel::SaveVector(GX_HANDLE _hLine, const vector<double> & V) {
   if (hLine != _hLine) {
      GetLine(_hLine, V.size(), true);
   }
   GX_DOUBLE * pData = getDoublePointer();
   memcpy(pData, &V[0], V.size()*sizeof(V[0]));
   ReplaceData();
}

///This routine gets called 10 times
 bool SpecRatio::DoWork(GX_HANDLE_PTR pLine) {
   if (!(hKin.GetLine(*pLine, true) && hUin.GetLine(*pLine, true) && hTHin.GetLine(*pLine, true))) {
      return true;
   }
   vector<double>vK = hKin.GetVector();
   vector<double>vU = hUin.GetVector();
   vector<double>vTh = hTHin.GetVector();

   if ((vK.size() == 0) || (vU.size() == 0) || (vTh.size() == 0)) {
      return true;
   }
   ///TODO: confirm all vectors the same lenghth
   len = vK.size();
   vUK.clear();  // these 3 vectors are declared as private class members
   vUTh.clear();
   vThK.clear();
   vUK.reserve(len);
   vUTh.reserve(len);
   vThK.reserve(len);

   // TODO: ensure everything is same fidincr, fidstart and length

   for (int i = 0; i < len; i++) {
      if (vK.at(i) < MinK) {
         vUK.push_back(rDUMMY);
         vUTh.push_back(rDUMMY);
         vThK.push_back(rDUMMY);
      } else {
         vUK.push_back(RatioPoint(vU, vK, i, UMin, KMin));
         vUTh.push_back(RatioPoint(vU, vTh, i, UMin, ThMin));
         vThK.push_back(RatioPoint(vTh, vK, i, ThMin, KMin));
      }

   }
   hUKout.setFidParams(hKin);
   hUKout.SaveVector(*pLine, vUK);
   hUTHout.setFidParams(hKin);
   hUTHout.SaveVector(*pLine, vUTh);
   hTHKout.setFidParams(hKin);
   hTHKout.SaveVector(*pLine, vThK);
   return TestError();
}

double SpecRatio::VValue(vector<double>V, int Index) {
   double result;
   if ((Index < 0) || (Index >= len)) {
      result = 0;

   } else {
      try {
         result = V.at(Index);
         if (OasisUtils::isDummy(result)) {
            result = 0;
         }
      }
      catch (out_of_range) {
         result = 0;
      }
   }
   return result;
}

double SpecRatio::RatioPoint(vector<double>Num, vector<double>Denom, int Index, double NumMin, double DenomMin) {
   double num = VValue(Num, Index);
   double denom = VValue(Denom, Index);
   int s = 0;
   // Search equalled 10 in this case
   while (((num < NumMin) || (denom < DenomMin)) && (s < Search)) {
      num += VValue(Num, Index - s) + VValue(Num, Index + s);
      denom += VValue(Denom, Index - s) + VValue(Denom, Index + s);
      s++;
   }
   if ((num < NumMin) || (denom < DenomMin)) {
      return rDUMMY;
   } else {
      return num / denom;
   }

}

最高的AQTime违规者是：


  std :: _ Uninit_copy>，双*，std :: allocator> 3.65秒
  和115731点击
  
  std :: _ Construct 1.69秒和46450637命中
  
  std :: _ Vector_const_iterator> :: operator
  ！= 1.66秒和46566395命中，依此类推...


std::allocator<double>::construct，
operator new，
std::_Vector_const_iterator<double, std::allocator<double> >::operator ++，std::_Vector_const_iterator<double, std::allocator<double> >::operator *
std::_Vector_const_iterator<double, std::allocator<double> >::operator ==

每个被调用超过4600万次。

我显然做错了所有这些对象的创建。谁能看到我的错误？

最佳答案

这是因为您要按值传递函数参数。每次按值传递std::vector时，都必须复制向量的完整副本。

更改这些：

double SpecRatio::VValue(vector<double>V, int Index) {

double SpecRatio::RatioPoint(vector<double>Num, vector<double>Denom...

至：

double SpecRatio::VValue(const vector<double> &V, int Index)

double SpecRatio::RatioPoint(const vector<double> &Num, const vector<double> &Denom...

因为为了您的使用，您实际上并不需要制作这些向量的单独副本。