Segmentation fault on set assignment

[bibo]

typedef struct {
pair<int,int> cr;
set<pair<int, int>> mem;
int cost;
bool changeX;
}Node;

Node* gn() {
return (Node *)malloc(sizeof(Node));
}

int minimumMoves(vector<string> grid, int startX, int startY, int goalX, int goalY) {

queue<Node* > q;
Node* tn;

int n = grid.size();
int minStepCount = n*n+100;

Node* start = gn();
start->cr = make_pair(startX, startY);
start->cost = 0;
start->changeX = true;
set <pair<int, int>> s;
s.insert(make_pair(startX, startY));
start->mem = s; // Segmentation error
q.push(start);
....
}
With gdb I see line `start->mem = s` gives error
Program received signal SIGSEGV, Segmentation fault.
0x0000000000404810 in std::_Rb_tree<std::pair<int, int>, std::pair<int, int>, std
::_Identity<std::pair<int, int> >, std::less<std::pair<int, int> >, std::allocato
r<std::pair<int, int> > >::_Reuse_or_alloc_node::_Reuse_or_alloc_node (
this=0x7fffffffe7b0, __t=...) at /usr/include/c++/6/bits/stl_tree.h:386
386 if (_M_nodes->_M_left)

[MikeyBoy]

std::set is a C++ class. If you use C memory allocation to allocate space for it, the constructor won't be invoked, so you don't have a working, initialised std::set object, just some uninitialised memory.

You need to use C++ memory allocation to create your object.

[Ganado]

You're writing C++, so why are you using malloc instead of new?

If you use new, I bet the segfault will go away.

Node* gn() {
    return new Node;
}

[doug4]

Better C++ usage would be:

#include <iostream>
#include <set>
#include <utility>
#include <memory>

struct Node
{
        std::pair<int, int> cr;
        std::set<std::pair<int, int>> mem;
        int cost;
        bool changeX;
};

std::unique_ptr<Node> gn()
{
    return std::make_unique<Node>();
}

int main()
{
    std::unique_ptr<Node> myNode = gn();
    return 0;
}

[bibo]

Thanks everyone. I changed the struct Node to class Node..

[doug4]

I changed the struct Node to class Node..

I hope you did something to gn() like @Ganado or I suggested, because simply changing struct Node to class Node will do absolutely nothing.

[TheIdeasMan]

Without any access specifiers changing the struct to a class would make all the member variables private, making the situation much worse ….

I fail to see how the OP can say that it would make it work now.

Even with the public specifier, it would make no difference, as doug4 says.