Function arguments 101
Arguments are just local variables (in the called function's scope) assigned by the caller of this function.
In my example, "x" was an argument of B. Since we invoked B with u, x is now assigned in B with the value of u from A.
Here is an example:
Code:
function A(x) [COLOR="DarkGreen"]-- x is an argument of A[/COLOR]
print(x)
end
A("Hello world!")
local y = "This is a test."
A(y)
It will print:
Hello world!
This is a test.
In this example, x is first assigned with "Hello world" and A prints it. Then y is assigned with "This is a test.", x is assigned with that value, and A prints it (although it cannot see x).
Another example just to be sure:
Code:
function max(a, b)
if a > b then return a end
return b [COLOR="DarkGreen"]-- Only executed if "a" is NOT greater than "b". That is, "a" is lesser than or equal to "b".[/COLOR]
end
print(max(1,3)) [COLOR="DarkGreen"]-- Will print 3[/COLOR]
print(max(5,6)) [COLOR="DarkGreen"]-- Will print 6[/COLOR]
print(max(4,2,6)) [COLOR="DarkGreen"]-- Will print 4, the third argument is ignored since "max" did not declare it[/COLOR]
print(max(4)) [COLOR="DarkGreen"]-- Will throw an error when a > b is tested: cannot compare number with nil. Indeed "b" is nil since it was not assigned with a value.[/COLOR]
Now look at your last piece of code: your function requests three arguments (iX, iY and iPlayer). You provide two arguments to it (pPlot and pPlayer). So iX now has the value of pPlot, iY has the value of pPlayer and iPlayer is nil. Hence an error.
Is it clear like that?
Understanding a code: step by step
You need to learn how to mentally run your code step by step. Here is one of your previous code:
Code:
function IsOverseasLocation(iPlayer, pPlot)
[COLOR="DarkGreen"]-- Entry point[/COLOR]
for iPlayer=0, GameDefines.MAX_MAJOR_CIVS-1 do [COLOR="DarkGreen"]-- Line 1[/COLOR]
local pPlayer = Players[iPlayer] [COLOR="DarkGreen"]-- Line 2[/COLOR]
if not (pPlayer:IsAlive()) then [COLOR="DarkGreen"]-- Line 3[/COLOR]
return [COLOR="DarkGreen"]-- Line 4[/COLOR]
else
local capitalPlot = pPlayer:GetStartingPlot() [COLOR="DarkGreen"]-- Line 5[/COLOR]
return capitalPlot:GetArea() ~= pPlot:GetArea() [COLOR="DarkGreen"]-- Line 6[/COLOR]
[COLOR="DarkGreen"]-- Line 7[/COLOR]
end
end
end [COLOR="DarkGreen"]-- Exit point[/COLOR]
* The function enters at "entry point". iPlayer and pPlot have the values provided by the caller.
* On line 1 iPlayer is assigned with 0. Since 0 is lesser than GameDefines.MAX_MAJOR_CIVS-1 we jump at line 2
* On line 2 pPlayer is assigned with the correspond player for iPlayer
* On line 3 we check that pPlayer is dead. Let's assume it is, we jump at line 4.
* On line 4 we return nothing. Jump to exit point, end of the function.
Now let's assume the player 0 was alive. Back to line 3.
* On line 3, pPlayer is alive, jump to line 5
* On line 5 capitalPlot is assigned with pPlayer's starting plot
* On line 6 we return false if the starting plot is on the same area than the provided plot argument, true otherwise. Jump to exit point, end of the function.
As you can see the other players are never tested, whatever the sequence of events is. We never reach line 7 and we never go back to line 1. We always return during the player 0's run.
Debugging 101
Sometimes, although you do a mental step by step execution, you still cannot understand. This happens, human brains are not perfect. So we need debugging techniques to understand what happens. Nowadays programmers have powerful tools for that but not here, in civ5 modding, you're out of luck. So you need to use the most basic debugging tool: "print".
The principle is easy to understand: add print statement as often as it is necessary for you to understand what happens. Add them until you understand what works and does not work. An example:
Code:
function IsOverseasLocation(iPlayer, pPlot)
print("entry point ", iPlayer, iPlot)
for iPlayer=0, GameDefines.MAX_MAJOR_CIVS-1 do
local pPlayer = Players[iPlayer]
print("#01 ", iPlayer)
if not (pPlayer:IsAlive()) then
print("player is dead")
return
else
print("player is alive")
local capitalPlot = pPlayer:GetStartingPlot()
print(capitalPlot:GetArea(), pPlot:GetArea())
return capitalPlot:GetArea() ~= pPlot:GetArea()
end
end
print("Natural end of the function")
end
Run that and it will be easy to understand!
As you noticed, we can provide many args to "print", they will be printed with tabulations between them. You could also use concatenations (.. operator, as in "a".."b" that produces the "ab" string) but beware to nil values when concatenating (you can use tostring to overcome the problem).
