is_undefined

This function returns whether a given variable is defined or not. In some cases you want to check and see what data type a variable holds in GameMaker and that's when you would use this function. It returns true or false depending on whether the value is defined or not.

NOTE This function cannot be used to verify the existence of a variable. Use variable_instance_exists() or variable_global_exists() instead.

Syntax:

is_undefined(n);

Returns:

Boolean

Example:

var val = ds_map_find_value(map, 13);
if is_undefined(val)
{
    show_debug_message("Map entry does not exist!");
}

The above code checks the variable "val" to see if it is undefined or not and shows a debug message if it is.