通过一次调用 c++ 将整个二进制文件读取到数组中

Question

我正在尝试将二进制文件读入结构数组

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;
};

下面的代码可以工作，但是一次只执行一个元素，通过将每个新元素推入一个数组，

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();
  }
}

我想通过一次读取整个数组来加快速度，这我认为应该类似于以下内容

    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;
}

但是读取导致了段错误，我该如何解决这个问题？

Answer 1

这是错误的：

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

您要将数据读入向量，您应该调整它的大小，而不仅仅是保留，如下所示：

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

这也是错误的：

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

您没有在那里重写向量的数据，而是覆盖了结构本身，还有谁知道还有什么。应该是这样的：

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

正如尼莫所说，这不太可能提高你的表现。

Answer 2

您的 features 的类型是 std::vector 并且将其大小写为 char。类型向量不是数组。

Answer 3

我认为您想要

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

您还需要确保 size 是 sizeof(FeaturePoint) 的倍数。否则，你会读得有点太多。