从地图内的stl地图中删除...在方法内

Question

so i'm trying to implement a File-system in c++. i have a Directory Class which holds a map. each directory can hold inside it's map another directory (so i have a map inside a map)

i'm trying to delete a file/directory, inside the method it deletes and all is well, but the method is done my main map doesn't update...

here the relevant code:

Directory Class (implemented using Composite):

class Directory : public FileComponent
{
private:
std::map<std::string,FileComponent*> directoryList;
public:
std::map<std::string, FileComponent*> &getMap() {
    return directoryList;
}

class fileSystem:

private:
FileComponent* find(Mode mode, const std::string& newDirectory, const std::string& directoryName, std::map<std::string, FileComponent*> check);
std::map<std::string,FileComponent*> fileSystem;

};

here's what i tried to do (finding a file and copying it...)

void filesys::copy(const std::string& fileName, const std::string& directoryName){
//looking for file
mapitr itr = fileSystem.find(fileName);
if (itr != fileSystem.end()){
    fileSystem.erase(itr);
    //file found, looikng for directory
}
else{
    for (itr = fileSystem.begin(); itr != fileSystem.end(); itr++){
        FileComponent* toCopy = find(CopyFile, fileName, directoryName, itr->second->getMap());
        if (toCopy != nullptr)
            //found! need to copy
            break;
    }
}

}

and my find method:

FileComponent* filesys::find(Mode mode,const std::string& newDirectory, const std::string& directoryName, std::map<std::string,FileComponent*> check){
else if (mode == CopyFile){
     mapitr itr = check.find(newDirectory);
     if (itr != check.end()){
         FileComponent* toCopy = itr->second;
         check.erase(itr);
         return toCopy;
     }
     else{
         for (itr = check.begin(); itr != check.end(); itr++){
             FileComponent* toCopy;
             try{
             toCopy = find(CopyFile, newDirectory, directoryName, itr->second->getMap());
             if (toCopy != nullptr){
                 return toCopy;
             }
             }
             catch (mExceptions& e){
                 e.what();
             }

         }
         return nullptr;
     }
 }

}

inside the function it finds and erases and all seems to be in order... however once returning the directory/file is still inside my filesystem... i'm returning my inside map by reference... so i really am out of ideas why it doesn't want to work...

thanks in advance!

Answer 1

You're passing the argument check (the map) by value to the find function. That means the data is copied and you only work on the copy and not the original. You should pass it by *reference instead:

std::map<std::string,FileComponent*>& check

---

On an unrelated note, the function name find is not a good name, it doesn't really describes what the function really does, which is find and erase.

Answer 2

In

filesys::find(Mode mode,
              const std::string& newDirectory,
              const std::string& directoryName,
              std::map<std::string, FileComponent*> check)

you pass check by value, not by reference, so you modify a copy, not the original.