在單個調用c ++中將整個二進制文件讀入數組

Question

我試圖將二進制文件讀入結構數組

struct FeaturePoint
{  
  FeaturePoint (const int & _cluster_id, 
            const float _x, 
            const float _y, 
            const float _a, 
            const float _b
            ) : cluster_id (_cluster_id), x(_x), y(_y), a(_a), b(_b) {}
  FeaturePoint (){}
  int cluster_id; 
  float x;
  float y;
  float a;
  float b;
};

下面的代碼可以工作，但是通過將每個新元素推送到數組上，一次完成這一個元素

void LoadImageFeaturesFromBinaryFile(const char * FileName, std::vector<FeaturePoint>& features )
{
  char strInputPath[200];
  strcpy (strInputPath,"/mnt/imagesearch/tests/");
  strcat (strInputPath,FileName);
  strcat (strInputPath,".bin");
  features.clear();
  ifstream::pos_type size;
  ifstream file (strInputPath, ios::in|ios::binary|ios::ate);
  if (file.is_open())
  {
    size = file.tellg();
    cout<< "this file size is : "<<size<<" for "<<strInputPath<<" " <<sizeof( FeaturePoint )<<endl;
    file.seekg (0, ios::beg);
    while (!file.eof())
    {
      try
      { 
        FeaturePoint fp;
        file.read( reinterpret_cast<char*>(&fp), sizeof( FeaturePoint ) );  
        features.push_back(fp); 

      }
      catch (int e)
      { cout << "An exception occurred. Exception Nr. " << e << endl; }
    }

    sort (features.begin(), features.begin()+features.size(),CompareClusterIndexes);  
    file.close();
  }
}

我想通過立即讀取整個數組加快速度，我認為應該看起來像下面這樣

    void LoadImageFeaturesFromBinaryFile(const char * FileName, std::vector<FeaturePoint>& features )
{
  char strInputPath[200];
  strcpy (strInputPath,"/mnt/imagesearch/tests/");
  strcat (strInputPath,FileName);
  strcat (strInputPath,".bin");
  features.clear();
  ifstream::pos_type size;
  ifstream file (strInputPath, ios::in|ios::binary|ios::ate);
  if (file.is_open())
  {
    size = file.tellg();
    file.seekg (0, ios::beg);
    features.reserve( size/sizeof( FeaturePoint ));
    try
    { 
      file.read( reinterpret_cast<char*>(&features),  size );  
    }
    catch (int e)
    { cout << "An exception occurred. Exception Nr. " << e << endl; }

    sort (features.begin(), features.begin()+features.size(),CompareClusterIndexes);  
    file.close();
  }
  else cout << strInputPath<< " Unable to open file for Binary read"<<endl;
}

但是讀取導致了seg故障，我該如何解決？

Answer 1

這是錯的：

features.reserve( size/sizeof( FeaturePoint ));

您將要將數據讀入向量，您應該調整它的大小，而不僅僅是保留，如下所示：

features.resize( size/sizeof( FeaturePoint ));

這也是錯的：

file.read( reinterpret_cast<char*>(&features),  size );

你沒有在那里寫過矢量數據，你要覆蓋結構本身，以及誰知道還有什么。 它應該是這樣的：

file.read( reinterpret_cast<char*>(&features[0]),  size );

就像Nemo說的那樣，這不太可能改善你的表現。

Answer 2

你的features類型是一個std :: vector，你將它包裝成char。 類型矢量不是數組。

Answer 3

我想你想要的

file.read( reinterpret_cast<char*>(&features[0]),  size );

您還需要確保size是sizeof(FeaturePoint)的倍數。 否則，你會讀得太多。