Question

I’m getting this error in several methods for several variables (all of which are vectors):

error: ‘parent’ was not declared in this scope

I’ve tried wrapping my method implementations inside of “namespace DisjointSubsets { … }”, but that causes other problems. It seems to only do this for vectors, and I’ve tried adding a “#include vector” at the start of the cpp file, it didn’t change anything.

Here is the header file:

#ifndef UNIVERSE 
#define UNIVERSE 
#include <vector>
class DisjointSubsets { 
    public :
        DisjointSubsets ( unsigned numberElements = 5 ) ;
        unsigned findDS ( unsigned ) ;
        bool unionDS ( unsigned , unsigned ) ;
    private :
        vector<unsigned> parent ;
        vector<unsigned> rank ;
        unsigned size ;
} ;
#include "DisjointSubsets.cpp"
#endif

And here is an example of one of the methods I wrote in the cpp file (which has no #includes):

unsigned DisjointSubsets::findDS(unsigned index) {
    return parent[index];
}

(Changed the method to be non-functional, but still illustrate the kind of line that would cause a problem. Just in case someone else working on the assignment stumbles across this.)

Answer 1

You must use std::vector<unsigned> instead of just vector<unsigned> to declare parent because vectoris declared in the std namespace.
Therefore you could also use using namespace std; before declaring the class.

However most people I know would discourage you from using the second form in a header file.
See the C++ FAQ for a more elaborate discussion on this topic.