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Handling map of files in c++

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佛祖请我去吃肉
佛祖请我去吃肉 2020-12-20 18:50

I need to write to a bunch of files simultaneously, so I decided to use map .

map MyFileMap;
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  • 悲&欢浪女
    悲&欢浪女 (楼主)
    2020-12-20 19:20

    std::map can't possibly work, because std::map requires its data type to be Assignable, which std::ofstream isn't. In the alternative, the data type must be a pointer to ofstream -- either a raw pointer or a smart pointer.

    Here is how I would do it, using C++11 features:

    #include 
#include 
#include 
#include 
#include 

int main (int ac, char **av)
{
  // Convenient access to argument array
  std::vector fileNames(av+1, av+ac);

  // If I were smart, this would be std::shared_ptr or something
  std::map fileMap;

  // Open all of the files
  for(auto& fileName : fileNames) {
    fileMap[fileName] = new std::ofstream("/tmp/xxx/"+fileName+".txt");
    if(!fileMap[fileName] || !*fileMap[fileName])
      perror(fileName.c_str());
  }

  // Write some data to all of the files
  for(auto& pair : fileMap) {
    *pair.second << "Hello, world\n";
  }

  // Close all of the files
  // If I had used std::shared_ptr, I could skip this step
  for(auto& pair : fileMap) {
    delete pair.second;
    pair.second = 0;
  }
}

    and the 2nd verse, in C++03:

    #include 
#include 
#include 
#include 
#include 

int main (int ac, char **av)
{
  typedef std::map Map;
  typedef Map::iterator Iterator;

  Map fileMap;

  // Open all of the files
  std::string xxx("/tmp/xxx/");
  while(av++,--ac) {
    fileMap[*av] = new std::ofstream( (xxx+*av+".txt").c_str() );
    if(!fileMap[*av] || !*fileMap[*av])
      perror(*av);
  }

  // Write some data to all of the files
  for(Iterator it = fileMap.begin(); it != fileMap.end(); ++it) {
    *(it->second) << "Hello, world\n";
  }

  // Close all of the files
  for(Iterator it = fileMap.begin(); it != fileMap.end(); ++it) {
    delete it->second;
    it->second = 0;
  }
}

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