Global Variables

This section explains what global variables are and how to use them.

A basic description of a global variable is one that, once declared, belongs to no instance in particular and yet can be accessed by all. Just like local variables, global variables must be declared, but unlike a local variable, a global variable remains in memory until the end of the game. So, you can create a global variable to keep track of (for example) the number of bullets that the player has and then just update this variable at different points in the game. A global variable does not belong to any specific instance and can be accessed, changed and used by all instances at any time, but any change made to the variable are "global", in that all instances using the variable will be affected by the change. Let's have a look at an example: = 5;

We declare the "food" variable by first writing "global" and then a "." to tell GameMaker that this variable is now global scope. We will need to use this method from now on any time we are required to access or to change this variable in any way. So, we have created a new variable called "food" and we have declared it as global. Now, any instance can use and change this variable in any way and all other instances will "see" this. For example we could have a different food object that the player collides with and in the collision event we have: +=1;

We also have another object that draws this value like this:

draw_text(32, 32, "food = " + string(;

With global variables we can change values and see those changes reflected in all instances of the objects that reference this variable. As with local variables you have to take care not to name your global variables the same as any instance variables as that will cause you problems and make bugs creep into your games due to variable overlap, which can be a difficult issue to debug sometimes. In general you should have a single script or object that declares all your global variables at the very start of the game (for example, in the Room Start Event), so that they are initialised and ready for any instance to use, and this also gives you a handy place to go back and reference should you need to check a variable name.

GameMaker: Studio has a collection of "built in" global variables too, so you should be aware of them as you may name one of your instance variables the same or wish to have your own global variable with the same name and wonder why you are getting errors! They are easy to spot, however, as they are shown in a different colour in the code editor and also come up in the auto-complete bar at the bottom. the majority of built in global variables are very specific and will only be used on rare occasions, but there are three in particular which are very useful and you can find out more about them from the pages listed below:

  1. score
  2. health
  3. lives
  4. async_load


The following method can also be used to declare global variables, but it is only included for backwards compatibility, and it is not recommended that you use this method for new projects as future versions of GameMaker: Studio may not support it.

The second method for creating global variables is to declare them as such using the globalvar declaration, much as you would a local variable using the var declaration. For example:

globalvar food;
food = 5;

Once declared in this way that variable is now considered global and requires no "global." prefix - which also means that it's a lot harder to identify global variables in your code and it's also much easier to get variable overlap as you use the same variable name in different objects - and the variable is accessed as follows:

food += 2;


draw_text(32, 32, "food = " + string(food));

Back: Variables And Variable Scope
Next: Instance Variables
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