映射两个键值

Question

I have an assignment where I need to go through all the files in a folder. For each file I need to know each unique file extension, how many files for each unique file extension, and the total size for each unique file extension. I have to be able to sort through this using either the file extension or the total size of the file extension. The first thing I thought of using was a map. This will keep track of each unique file extension and the amount of times that file extension was found. How do I now associate the total size of the file extension to my map? So for example I need the output to be something like this:

Using file extension for sort .cpp : 1 : 3400 .exe : 3 : 3455600 .mp4 : 25 : 200000404

Using total file extension size for sort .mp4 : 25 : 200000404 .exe : 3 : 3455600 .cpp : 1 : 3400

Here is the code I have after some editing:

    #include <iostream>
    #include <filesystem>
    #include <map>

    using namespace std;
    using namespace std::tr2::sys;

    class fileInfo {
    public:
        int fileCount;
        long long fileSize;
    };

    void scan(path f)
    {
        map<string, fileInfo> fileMap;
        cout << "Scanning = " << system_complete(f) << endl;
        directory_iterator d(f);
        directory_iterator e;
        for( ; d != e; ++d)
        {
            path p = d->path();
            cout << "\nExtension is: " << extension(p) << "\tFile size is: " << file_size(p) << endl;
            fileMap[extension(p)].fileCount ++;
            fileMap[extension(p)].fileSize += file_size(p);
        }

        for (map<string, fileInfo>::iterator it = fileMap.begin(); it != fileMap.end(); ++it)
        {
             cout << it->first << " : " << it->second.fileCount << " : " << it->second.fileSize << endl;
        }
    }

    int main(int argc, char* argv[] )
    {
        path folder = "..";

        scan(folder);

        return 0;
     }

EDIT: So I have implemented the class fileInfo. It is sort of working. But I am having a problem with the file_size. After the first run through the loop, it correctly returns the file_size, but for every other run through the loop file_size is returning 0.

Answer 1

You can create one map:

 map<string, vector<int> > fileExtToSizeMap;

Basically, for each file extension in string format, if the current file is associated with that extension, put the size of the file into the vector vector<int> . After you finished scanning the directory, the size of that vector will tell you how many files are associated with the file extension and the sum of the vector will tell you the total size for each unique file extension . You two major questions are then answered by this data structure.

Answer 2

I would create a data structure eg ExtensionStat like this:

struct ExtensionStat {
  int totalFile;
  int totalSize;
};

And have a map from extension name into the stat

map<string, ExtensionStat> extMap;

Then you just iterate contents of your folder collecting the statistics into extMap . Keep in mind you don't need to use struct, you can use class too. Also you can choose the map to be map<string, ExtensionStat*> extMap; if you'd like to avoid full value copying

Answer 3

You could also use a multi-map

map<string, size_t> fileExtSizeMap;

Simple add a new entry for every file encountered.

std::lower_bound and std::upperbound can be used to search this structure. Use std::distance on resulting iterators to get a file count.

Or simply iterate through the complete map incrementing a counter as you go.