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.