C++ double pointer not known conversion - c++

Question

I am literally freaking out on the following :
template <class T> // int, float, double etc..
class Graph {
public:
// Documentation, it has to be between [0..100]
Graph(int size = 10, int density = 10, T range = 0):
m_size(size),
m_density(density),
m_range(range) {
generate();
}
~Graph() {
for (int i = 0; i < m_size; i++)
delete[] m_graph[i];
delete[] m_graph;
}
[..]
static Graph<T>* custom(T** cgraph, int size, T range) {
Graph<T> *graph = new Graph<T>(size, 10, range);
for (int i = 0; i < size; i++)
delete[] graph->m_graph[i];
delete[] graph->m_graph;
graph->m_graph = cgraph;
}
private:
T** m_graph;
[ .. ]
};
int nodes[4][4] = {
{ 6, 5, 2, 5 },
{ 5, 6, 3, 3 },
{ 1, 3, 6, 1 },
{ 5, 3, 1, 6 }
};
int main() {
Graph<int> *graph = Graph<int>::custom(nodes, 4, 5);
}
What is it poorly failing to compile reporting the following errors ?
g++ graph.cpp -o test_graph
graph.cpp: In function ‘int main()’:
graph.cpp:191:55: error: no matching function for call to ‘Graph<int>::custom(int [4][4], int, int)’
Graph<int> *graph = Graph<int>::custom(nodes, 4, 5);
^
graph.cpp:60:20: note: candidate: static Graph<T>* Graph<T>::custom(T**, int, T) [with T = int]
static Graph<T>* custom(T** cgraph, int size, T range) {
^
graph.cpp:60:20: note: no known conversion for argument 1 from ‘int [4][4]’ to ‘int**’
It looks so right to me, what's wrong ?

Answer 1

You need to make nodes by an array of pointers to int.
int nodes_v[4][4] = {
{ 6, 5, 2, 5 },
{ 5, 6, 3, 3 },
{ 1, 3, 6, 1 },
{ 5, 3, 1, 6 }
};
int *nodes[4] = { nodes_v[0], nodes_v[1], nodes_v[2], nodes_v[3] };
You also need to add an additional member to the Graph variable to mark that it is a custom graph, and if set, the destructor should not delete the memory.
Best to give Graph a private constructor which passes in the custom flag and doesn't bother allocating the memory if set.
Graph(int size, int density, T range, bool custom):
m_size(size),
m_density(density),
m_range(range),
m_custom {
}
Graph(int size = 10, int density = 10, T range = 0):
Graph(size, density, range, false) {
generate();
}
static Graph<T>* custom(T** cgraph, int size, T range) {
Graph<T> *graph = new Graph<T>(size, 10, range, true);
graph->m_graph = cgraph;
}
Finally, you need to handle copy constructor and assignment operator (start by just deleting them).