c++ - Why must my global variable be declared as a pointer? -

when compiling c++ program receive no errors, within unordered_map hash function fails, attempting mod 0. (line 345 of hashtable_policy.h of stl)

i've found fix, don't know why i'm having problem begin with. struct looks this, (sorry specific code.)

struct player { private:     entity& entity = entitymanager->create(); public:     player() {         entity.addcomponent(new positioncomponent(0, 0)); // add component uses unordered map.     } }; player playerone; // error perpetuates through constructor. 

however, if declare playerone pointer, so:

player* playerone; 

and call:

playerone = new player(); 

i not have issues.

i've been searching - no success. doing wrong?

when use player global, you've no idea if entitymanager (presumably global) has been initialised yet - order of initialisation of globals isn't defined.

when use pointer , initialise new (in main(), presume), globals have been created then, code works.

this highlights 1 of reasons why global variables bad idea.