I'm inheriting from shared_ptr<void> to store an extra filed length that shows the length of memory allocated by malloc function.

I'm also passing free as a custom delete function.

// a chunk of memory that will automatically be deleted
struct bytes : public std::shared_ptr<void> {
public:
   unsigned int length;
   bytes(std::nullptr_t) :
       std::shared_ptr<void>(nullptr),
       length(0) { }
   bytes(int len) :
       std::shared_ptr<void>(malloc(len), free),
       length(len) { }
};

// a sample use case
bytes foo(int n){
   if( condition1)
      return nullptr;
   bytes b(100);
   // ....
   fread(b.get(),1,100,file_pointer);
   // ....
   return b;
}

I'm just not sure if this code has hidden bugs or not ? (I'm new to c++11).