Question

I’ve been trying every tip provided on this site, but none worked, so I’m going to explain what my issue is.

I’m tyring to sort a vector containing pointers to objects, so of couse I can’t use the std::sort(vector.begin(), vector.end()) syntax because it would use the “<” operator on pointers. Here is a sample of my code :

// Vertex.h
class Vertex
{
    public :
        inline int getPond() const {return m_Pond;}

    private :
        int m_Pond;
}

.

//Graph.h
class Graph
{
    public :
        void sortVertexPond(vector<Vertex*> VertexVect);
        inline bool compareVertex(const Vertex* LeftVertex, const Vertex* RightVertex){return (LeftVertex->getPond() < RightVertex->getPond());}
        void testFunct ();

    private :
        vector<vector Vertex*>> m_VertexByLayers;
}

.

//Graph.cpp
#include <algorithm>

void Graph::sortVertexPond(vector<Vertex*> VertexVect)
{
    std::sort(VertexVect.begin(), VertexVect.end(), compareVertex);
    //std::sort(VertexVect.begin(), VertexVect.end(), compareVertexStruct());
}

/*struct compareVertexStruct {
bool operator ()(Vertex* LeftVertex, Vertex* RightVertex) {return (LeftVertex->getPond() < RightVertex->getPond()); }
};*/

void testFunct()
{
    this->sortVertexPond(m_VertexByLayers.at(0));
}

This won’t compile as I get the following error :

error C2780: 'void std::sort(_RanIt,_RanIt)' : 2 arguments expected - 3 provided

As you can see in the code I provided, I already tried to do it by creating a Functor. This way I add no issues compiling and running, the odd thing is that even if my functor was called (which I could see by adding a cout inside my operator), std::sort didn’t sort anything.

I had this kind of results :

Input : [3,2,1]
3<2? 0
2<1? 0
Output : [3,2,1]

Input : [1,2,3]
1<2? 1
2<3? 1
Output : [1,2,3]

Could please anyone help me fix this?

PS : Sorry for my english, it isn’t my home language.

Edit : Thanks to all of you. Here’s what I did to fix it.

//Graph.h
class Graph
{
    public :
        vector<Vertex*> sortVertexPond(vector<Vertex*> VertexVect);
}


//Graph.cpp
#include <algorithm>

struct compareVertexStruct {bool operator ()(Vertex* LeftVertex, Vertex* RightVertex) {return (LeftVertex->getPond() < RightVertex->getPond());}};

vector<Vertex*> Graph::sortVertexPond(vector<Vertex*> VertexVect)
{
    std::sort(VertexVect.begin(), VertexVect.end(), compareVertexStruct());
    return VertexVect;
}

Answer 1

You are passing your vertex vector by value to sortVertexPond:

void Graph::sortVertexPond(vector<Vertex*> VertexVect)

Thus, you are making a copy when calling that function, and then sorting the copy, but the original is not changed.

Try passing the vector by reference:

void Graph::sortVertexPond(vector<Vertex*>& VertexVect) // Note the '&'