Functions

First native support for functions in GTA was added in Liberty City Stories. The games prior to that only had limited subroutines invoked with the gosub command. Those subroutines allowed to avoid code duplication; however, they were operating on the same scope as the code invoking them. Any variables used in a subroutine would alter the state of the script.

CLEO Library brought support for functions (dubbed scm func) in early versions, and it became important part of the modern scripting techniques. Each SCM function owns 16 or 32 local variables (depending on the game), none of them would clash with the local variables of the script calling the functions. CLEO5 improved SCM functions a lot by completely isolating script and function state, adding support for string arguments, and more.

Sanny Builder 4 adds new syntactic element to the language to easily create and use SCM functions in the code.

Visit this GitHub ticket for more technical information and examples on function syntax.

Syntax

To make a new function, use the function keyword.

function <signature>
<body>
end

signature defines function's input parameters and their type, and also an optional return type. body is the code that runs when you call the function. A function must end with the end keyword.

Functions are available anywhere in the current scope. Functions defined inside other functions only available in that function.

Example

function sum(a: int, b: int): int
  int result = a + b
  return result
end

Signature

A function's signature defines what types of input arguments the function receives and what type of value it returns. Function arguments may be of a primitive type int, float, string, or a class, e.g. Car or Pickup.

String arguments are only supported in CLEO 5. They are always passed as pointers.

A function may have zero parameters. If it has parameters, they are listed between (). Each parameter has a name and a type, separated by a colon. Parameter declaration syntax is similar to that of var..end. Each parameter can be used as a function's local variable in the function body.

function loadModel(modelId: int)
    request_model modelId
    while not is_model_available modelId
        wait 0
    end
end

modelId is an input parameter of the int type. It can be used as a local variable.

If the function returns something, its type has to be defined after the list of parameters (or the function name, if there are no parameters). E.g.:

function foo: float
function bar(i: int): int

Calling a Function

Functions can be called using its name followed by open and closed braces:

function foo
end

foo()

() are required for the function call, even if function receives no arguments. Without () function name is compiled as it's offset or address (if this is a static foreign function):

function foo
end

jump foo // jumps into the function body

Function Body

A function's body include all instructions executed when the main code calls the function. The function may have zero instructions. Function parameters can be referenced in the body as local variables. The function may create extra local variables and even new functions, available only within this function:

int x

function mod
  int x = 5  // this `x` only exists within function `mod`
end

x = 10
mod()
// x is still equal to 10

Return From Function

Function ends at the end keyword. You may exit early using the return keyword.

Exit from a function using return keyword is only supported in CLEO 5 (San Andreas). For other CLEO versions use cleo_return command.

function SetWantedLevel(level: int)
  set_max_wanted_level level
end // no explicit return, function ends here

function SetWantedLevel(level: int)
  if or
    level < 0
    level > 6
  then
     return // early return, code below won't be executed
  end
  set_max_wanted_level level
end // function ends here

Returning logical values

For a function to be used as a condition in IF..THEN, it must have a special return type: logical.

function check(): logical

if check()
then
end

logical function returns a result of logical expression, or true or false.

return true
return false
return 0@ == 1
return Char.DoesExist(0@)

A value returned from a logical function sets the script's condition result and be combined with other checks in one IF statement.

function isDefined(val: int): logical
  if val <> 0
  then return true
  else return false
  end
end

if isDefined(5)
then
  // result is true
else
  // result is false
end

The example above can also be written in a more concise way:

function isDefined(val: int)
  return val <> 0
end

Returning Values

The function may return one or multiple values, using the return keyword.

To define a function that returns something, add a colon and a type at the end of the function signature:

function maxItems: int

To return a value use return followed a value:

return 5

To read the returned value, a caller must provide a variable:

int value = maxItems() // value is 5

Returning any value, even 0, from a function is considered a success if the function is used as a condition.

function zero: int
  return 0
end

if
  zero()
then
  // success
else
  // will never be here
end

If a function may fail and not have a valid result, its return type should be marked as optional and a blank return can be used:

function createCar: optional int
  return
end

if
  Car c = createCar()
then
  // got a car handle in c
else
  // got nothing
end

optional keyword must precede the list of return types.

Optional Return Type

Some functions may not be able to return correct values (a fallible function). For example, a function reading a file may fail if the file does not exist. In this case the return type can be marked with the optional keyword:

function getValues: optional int, int, int
  if <...>
  then
     return 1 2 3
  else
     return
  end
end

Function getValues may return 3 integer values or nothing. On calling end, to check whether a fallible function succeeded it can be wrapped into IF..THEN condition like so:

int a, b, c
if
  a, b, c = getValues()
then
  // we got 3 values in a, b, c
else
  // we got nothing, a, b, c have not been changed
end

Foreign Functions

CLEO provides an interface for calling game's native functions. There are 4 opcodes that support different calling conventions:

0AA5: call_function {address} [int] {numParams} [int] {pop} [int] {funcParams} [arguments]
0AA6: call_method {address} [int] {struct} [int] {numParams} [int] {pop} [int] {funcParams} [arguments]
0AA7: call_function_return {address} [int] {numParams} [int] {pop} [int] {funcParams} [arguments] {var_funcRet} [var any]
0AA8: call_method_return {address} [int] {struct} [int] {numParams} [int] {pop} [int] {funcParams} [arguments] {var_funcRet} [var any]

As you may guess, using them directly is not very convenient. These opcodes have their own quirks, like having to provide input arguments in reverse order.

Sanny Builder 4 offers an interface for defining foreign functions in code and using them as regular functions. It can be done by adding calling convention type to a forward declaration.

function<cc[,address]>(args): return type

A cc or calling convention defines who's in charge of cleaning up the stack when function returns.

CLEO and Sanny Builder supports 3 major conventions:

cdecl - caller cleans up the stack
stdcall - callee cleans up the stack
thiscall - callee cleans up the stack. Since thiscall is a class method function, it additionally receives a pointer to the class instance in ecx register.

You can read more about different types of calling conventions on Wikipedia.

Optional address parameter defines where this function is located in the game memory (static functions). If this address can only be known in runtime, this parameter can be omitted.

A return type can be int, float, or string.

Example

function CStats__GetStatType<cdecl,0x558E30>(statId: int): int

int type = CStats__GetStatType(42)

// 0AA7: call_function_return {address} 0x558E30 {numParams} 1 {pop} 1 {funcParams} 42 {var_funcRet} 0@

This code invokes a function at address 0x558E30 with argument 42 and stores the returned value in the variable type.

Passing multiple arguments can be done as usual:

function Foo<stdcall,0x400000>(int, float): int

int value = Foo(10, 20.0)

// 0AA7: call_function_return {address} 0x400000 {numParams} 2 {pop} 0 {funcParams} 20.0 {var_funcRet} 10 0@

Calling a thiscall function requires the first argument to always be a pointer to the class instance.

function Destroy<thiscall,0x400000>(struct: int)

int instance = 0xDEADD0D0
Destroy(instance)

// 0006: 0@ = 0xDEADD0D0
// 0AA6: call_method {address} 0x400000 {struct} 0@ {numParams} 0 {pop} 0

When function's address is not known at compile time, you still can define a foreign function and use a function pointer to call it by reference. To declare a function pointer, declare a new variable with the function name as the type:

function Destroy<thiscall>(struct: int)
Destroy method // define a pointer to function Destroy
...
method = 0x400000 // function is located at 0x400000
method(0xDEADD0D0) // call function using the pointer

// 0006: 0@ = 0x400000
// 0AA6: call_method {address} 0@ {struct} 0xDEADD0D0 {numParams} 0 {pop} 0

Static function's name represents its address when used without ()

function Foo<stdcall,0x400000>(int, float): int

int addr = foo // addr = 0x400000

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Last updated 7 months ago