c++ - Initializing a complex object. Error when I don't? -

i can't seem figure out why program crashes every time node object. , can't make progress until working...

my problem is: whenever try "set data" on node x, access violation error. before getting runtime failure #3 not initializing variable. initialize null, , still error. previous node classes never gave me error, kinda stumped. appreciated!

here's code:

node class:

#ifndef node #define node  template <typename t> class node { public:     node();     node(t data);     void setdata(t data); private:     t m_data;  };  template <typename t> node<t>::node() {  }  template <typename t> void node<t>::setdata(t data) {     m_data = data; } #endif 

main:

#include <iostream> #include <crtdbg.h>  #include "node.h" #define _crtdbg_map_alloc  int main() {      _crtsetdbgflag(_crtdbg_alloc_mem_df | _crtdbg_leak_check_df);       node<int> * x = nullptr;      x->setdata(20);       return 0; } 

the weird thing is, whenever "new" allocate new node, problem doesn't occur.. in advance.

you dereferencing null pointer value results in undefined behavior. need create instance of node<int> , assign x so

node<int> * x = new node<int>(); x->setdata(20); 

or use automatic storage duration , declare x value.

node<int> x; x.setdata(20);