I am having issues coding a game, in terms of variables in objects. Whgen running i get this error

action number 1
of  Step Event0
for object obj_text_demo_player:

Variable obj_gameManager.<unknown variable>(100020, -2147483648) not set before reading it.
at gml_Object_obj_text_demo_player_StepNormalEvent_1 (line 1) - if  (obj_gameManager.ammo == 0)

and i have no clue hope to fix this, this is where the code is used.

obj_player (player - where the issue seems to be - STEP EVENT)

if (obj_gameManager.ammo == 0)
     obj_gameManager.weapon = "MachineGun";
    obj_gameManager.ammo = 50000;

obj_pickup (pickup object - COLLISION /W PLAYER OBJECT)

obj_gameManager.weapon = "Tri-Shooter";
obj_gameManager.ammo = 900;

Obj_gameManager (object variables are from - DRAW EVENT)

global.health = 100;
global.weapon = "MachineGun";
global.ammo = 50000;


draw_text(780, 300, global.weapon );
draw_text(780, 375, global.ammo );

Any help would be massively appreciated, as I'm new to Game Maker Studio. If you need any more info I'm happy to add it.


2 Answers 2


It seems to me that you didn't declare the variables in the Create event, since it says <unknown variable>. In the Create event of obj_gamemanager you need to setup like

this.ammo = 0;

And do that every single variable that you have, otherwise they won't exist.

  • \$\begingroup\$ I have tried this, both adding the global.ammo as well as trying "this.ammo" neither work, with "this.ammo" giving a different error entirely. \$\endgroup\$
    – K.Denn
    Apr 6, 2016 at 20:47
  • \$\begingroup\$ @K.Denn But did you tried to initialize the variable in the Create event? Without "using" the variable in the Create event, the variable won't exist \$\endgroup\$
    – DH.
    Apr 6, 2016 at 21:27
  • \$\begingroup\$ global.weapon = "MachineGun"; global.ammo = 50000; This is how i did it, is this the correct way? i also have tried the same thing but with "global" changed to "this" with the same result. If you would prefer, i can give you the GMK so you can look under the hood better. \$\endgroup\$
    – K.Denn
    Apr 6, 2016 at 21:32
  • \$\begingroup\$ @K.Denn Well... you can try to use global for now, but, everytime you try to read the variable it's global.variable, and not obj_gamemanager.variable. There's something troubling me though... the object with a problem is obj_text_demo_player when trying to access the obj_gamemanager, it looks like that it's trying to read obj_gamemanager as a variable and not as an actual instance. Can't help you now though, I don't have GMS here, but if IIRC, the color of obj_gamemanager should be different, I think it's golden color. \$\endgroup\$
    – DH.
    Apr 6, 2016 at 21:46
  • \$\begingroup\$ After making the adjustments the code now works, thanks. \$\endgroup\$
    – K.Denn
    Apr 6, 2016 at 21:54

In global game settings click "set uninitialized variables to 0".

This isn't recommended all the time in programming practices to assume undefined variables have initialized values, but if that is what you wish to do then so be it.


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