object hierarchy functions - c

Question

My task would be to make this object hierarchy and have a sum of all file sizes in the file system.
If I understand correctly this would be a multi level inheritance, but I'm not sure how to write a function what can run through every lower-level object and sum them up.
#include <iostream>
using namespace std;
class File{
public:
//File(int x){filesize=x;}
void setSize(int x){filesize=x;}
void showsize(){cout<<filesize<<endl;}
int getsize(){return filesize;}
private:
int filesize;
};
class Directory : public File {
public:
void SumDir(){
}
private:
int sumofdir=0;
};
int main()
{
File b;
b.setSize(416);
b.showsize();
return 0;
}

Answer 1

You could have the Directory class have a std::vector of File*. Then it would be just a simple walkthrough of each of these directory entries and in turn, invoke the getSize() on them. getSize() could be a polymorphic function that just either gets the size of the File if it's a regular file or the size of the entire directory if it's an instance of a Directory. Something on these lines:
#include <iostream>
#include <vector>
class File{
public:
explicit File(int x): fileSize(x){}
void setSize(int x){
fileSize=x;
}
void showSize() const{
std::cout<<fileSize<<'\n';
}
virtual size_t getSize() const{
return fileSize;
}
virtual ~File() = default;
private:
int fileSize;
};
class Directory : public File {
public:
Directory() : File(0){} //Directory is just a File of 0 size
size_t getSize() const override{
size_t size = 0;
for(auto const& file: dirEntries) {
size += file->getSize();
}
return size;
}
void addFile(File* file) {
if(file != nullptr) {
dirEntries.push_back(file);
}
}
private:
std::vector<File*> dirEntries;
};
int main() {
Directory child;
File f1{10}, f2{20};
child.addFile(&f1);
child.addFile(&f2);
Directory parent;
File f3{30};
parent.addFile(&f3);
parent.addFile(&child);
std::cout<<parent.getSize(); //60
}