在C ++中处理文件映射 [英] Handling map of files in c++

问题描述

我需要同时写入一堆文件，所以我决定使用 map< string，ofstream> 。

I need to write to a bunch of files simultaneously, so I decided to use map <string, ofstream>.

map<string, ofstream> MyFileMap; 

我采用 vector< string> FileInd ，由 a b c 组成，然后尝试使用以下命令打开我的文件：

I take a vector<string> FileInd, which consists of, say "a" "b" "c", and try to open my files with:

for (vector<string>::iterator it = FileInd.begin(); iter != FileInd.end(); ++it){
    ...
    MyFileMap[*it].open("/myhomefolder/"+(*it)+".");
}

我得到了错误

request for member 'open' in ..... , which is of non-class type 'std::ofstream*'

我试图切换到

map<string, ofstream*> MyFileMap;

但是它也不起作用。

有人可以帮忙吗？

谢谢。

说明：

我都尝试过

map< string，ofstream> MyFileMap;
map< string，ofstream *> MyFileMap;

两者都

.open
->打开

这四个变体都不起作用。

neither of 4 variants work.

解决方案（在下面的Rob代码中建议）：

基本上，我忘记了 ，以下对我有用：

Basically, I forgot "new", the following works for me:

map<string, ofstream*> MyFileMap;
MyFileMap[*it] = new ofstream("/myhomefolder/"+(*it)+".");

推荐答案

std :: map< std :: string，std :: ofstream> 可能无法工作，因为 std :: map 要求其数据类型为可分配的， std :: ofstream 不是。或者，数据类型必须是指向ofstream的指针-原始指针或智能指针。

std::map<std::string, std::ofstream> 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.

这是我使用C +的方式+11功能：

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

#include <string>
#include <map>
#include <fstream>
#include <iostream>
#include <vector>

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

  // If I were smart, this would be std::shared_ptr or something
  std::map<std::string, std::ofstream*> 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;
  }
}

和第二节经文，在C ++ 03中：

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

#include <string>
#include <map>
#include <fstream>
#include <iostream>
#include <vector>

int main (int ac, char **av)
{
  typedef std::map<std::string, std::ofstream*> 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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