c++ custom comprator for more than attribute - c++

Question

I am trying to implement a naive File System.
I have this class
class BaseFile {
private:
string name;
public:
BaseFile(string name);
string getName() const;
void setName(string newName);
bool operator < (const BaseFile& str) const;
bool operator > (const BaseFile& str) const;
virtual int getSize() = 0;
};
and the subclass
class Directory : public BaseFile {
private:
vector<BaseFile*> children;
Directory *parent;
public:
Directory(string name, Directory *parent); r
Directory *getParent() const;
void setParent(Directory *newParent);
void removeFile(string name);
void removeFile(BaseFile* file);
void sortByName();
bool SortSize(BaseFile& a , BaseFile& b);
void sortBySize();
vector<BaseFile*> getChildren(); n
int getSize();
string getAbsolutePath();
};
I need to sort the vector<BaseFile*> children once by the attribute size by activating the function SortBySize().
And by name by the function SortByName().
I cant use sort algorithm I want to use std::sort()
For the names I overloaded the operators < > and for the numbers(size) I want to define a custom comparison function.
I defined the function in the class Directory. I tried to make is static it didn't work
bool Directory::SortSize(BaseFile& a , BaseFile& b)
{
return (a.getSize() < b.getSize());
}
but when I use std::(children.begin(), children.end(), sortSize)
I get "invalid use of non-static member function".
Any help?

Answer 1

To sort by size using a lambda expression:
vector<BaseFile*> files;
std::sort(files.begin(), files.end(),
[](const BaseFile* a, const BaseFile* b)
{ return a->getSize() < b->getSize(); });