Lua return function. If object does not have a metatable, returns nil.
- Lua return function pack function, which you can use to store multiple return values in a table. lua" end And the somecode. ) return 0 in their C implementation. The named function syntax function add(a,b) return a+b end is actually a syntactic sugar for add = function(a,b) return a+b end. 9,498 4 4 gold badges 35 35 silver badges 41 41 bronze badges. 3 Lua: Functions with Multiple Returns This event happens when Lua tries to call a non-function value (that is, func is not a function). html file from GitHub. Whatever the return value of sum is, lua_pcall will (by itself) leave on the stack exactly the number of elements as the return value of the function (sum, in this case). this means if we don't pass argument to lua After it returns, Lua automatically removes whatever is in the stack below the results. Edit: I believe the solution to your problem will require binding at some level, without resorting to modifying the Lua interpreter or using a code translation step. If you wanted to create that entry, then write myfunc = true, to assign something that is not nil. They only compile the chunk to an internal representation and return the result, as an anonymous function. The time function, when called without arguments, returns the current date and time, coded as a number. method(self, arg1, arg2). function vals return 3, 7 end-- In the main part of our script-- Here we use the 2 different return values from the-- call with multiple assignment. The default function returns nil. Hot Network Questions Lua return from function problem. getting nil value for no apparent reason. How to access the return value of a C function called by lua_pcall? 0. Improve this answer. local func func = function ( n ) if n == 1 then return Functions are usually set with function a(b,c) end and rarely with setting a variable to an anonymous function (a = function(a,b) end). 1. When it finishes capturing characters, it's supposed to return the string to the calling function, but the calling function only gets nil. Lua userdata array access and methods. how to play with a function which return table in lua? 1. From Lua 5. )". The output passed to the i variable of the outer loop comes from the yield method, not from the return. 0. 5. The way you call start_polling and get_poll_params are correct and the multiple return values will be passed forward. local function values return 3, 7 end: Here we use the 2 different return values from the call with multiple assignment. Multiple results as part of the arguments in a function. But it does so in such a way that you can decompose them later: But it does so in such a way that you can decompose them later: From Lua 5. They enable easier code writing and In Lua, functions can return multiple values. Red() function factorial ( a ) if a <= 1 then return a end return a * factorial( a - 1 ) end Including Other Code. The return statement is used to specify the output of the function. It receives as arguments the non table value and the index. type(f) end end x Hi so I have been wondering, would you guys say its cleaner and more readable to use early returns in Roblox lua. pack, e. This would print each word on a separate line. new("E") f and t are newly created tables, each with an s field and both with the same metatable. 25. Hot Network Questions Prospective employers tell me my field is obsolete. b) are using non-precompiled Lua sources. The interpreter automatically calls meta. If you declare your variables outside of the if Lua return from function problem. It becomes global only if you make it global, so it is assigned without the "local" keyword. local aliasPrint = _ENV["print"] aliasPrint("Hello, World!") How can a Lua function return nil, even if the returned value is not nil inside the function? 0. how to get the second return value of a function in a if condition in Lua? Hot Network Questions lua (Syntax): Calling a function that returns more than 1 value, and using those values as arguments, but without extra lines of variable assignment? 2. name2 is nil; you're using the function call in a way that adjusts the number of return values to 1. Ask Question Asked 7 years, 7 months ago. The returned value shouldn't be nil. t = table. What it does is call the second function when the first one is called. The old function is Magic before it has been hooked. 函数的格式 function function_name() end 或者 a=function() end 函数声明之前，不能调用----与C#不同的是，C#在new的时候，就编译好了，就可以随时调用；lua要先声明，在调用 从第二种可以看出，func是一种变量类型。有点类似与c#中的委托和事件的写法 2. Next Previous There is a real difference: your code only works for one argument. lua by Cody Duncan ---Wraps the High Resolution Timer Functions in --- Timer. , io. Further, __pairs or __index might be futzing with the iteration, so you'd better go for k, v in next, obj, nil do to copy the actual contents (that's sort of the equivalent of rawget for pairs), Lua function return string with C++. Writing functions that create or use other functions (called "higher order functions") is a way to write programs declaratively (your program describe what you want done) rather No, meta does not return anything - at least nothing important. It can be used in two forms, the first one includes passing an index and then it will return the numbers that are passed after that number into the function as an argument in a list format, the other pattern is if we pass the length operator as a first argument, Using break return and goto . 753 6 6 silver badges 7 7 bronze badges. function only returning one value instead of both in lua. Viewed 874 times 4 If I want to Lua has built-in support for multiple results. Both function calls and vararg expressions can result in multiple values. Something along these lines:-- subsystem. execute("echo 'test'") then local t = "test" end This is a way to get what you want, i hope it helps you. Function return values. Note: functions are global by default. ]]--[ What you need to do is to return a table with the fields you want to access in subsystem. -- Here's a function that takes two numbers and returns their sum function plus(a, b) return a + b end -- In Lua, you don't need to specify parameter types or return types function plusPlus(a, b, c) return a + b + c end -- The main function in Lua is typically just the script itself, -- but we'll wrap it Quote from the require manual entry: "Once a loader is found, require calls the loader with two arguments: modname and an extra value dependent on how it got the loader. Not in general. A unique feature of Lua is the fact that functions can return any amount of values. Two functions, time and date, do all date and time queries in Lua. == Edit: As I mentioned, instead of using a global variable (the funcs above) you can store the reference to the function in the "registry". By buying the book, you also help to support the Lua project. But frankly, you won't see any speedup here, just will This function returns a lua_Object, which is the old fallback value, or nil on fail (invalid fallback name). 16. LuaPlus: How to make a function return a table? 5. return a + b end To quote one of the Lua authors in an e-mail on the Lua mailing list:. Lua: Functions with Multiple Returns. string is also a kind of reference type, but is immutable, interned and copy-on-write - it behaves like a value type, The weird thing is: the function only recognize the first word that is being checking, that is, the word sky. For example: return x, x, x. Any iterator needs to keep some state between successive calls, so that it knows where it is and how to proceed from there. pack(readFunc(1234, 32)) Or in C, if you want to return a table instead of a list of results, you need to first push a table onto the stack, and then push each item on the stack and add it to the table. That value will become the value of the function call expression. The callback function can be called a long time after digitButton did its task and after the local variable digit went out of scope, but it can still access that variable. This 本文将介绍如何在C语言中调用Lua函数。首先，需要了解的是，在Lua中定义的函数可以被C语言所调用，C语言程序需要使用Lua提供的API来实现这一功能。以下是C语言调 Let's have a go at writing some functions featuring return values. – Despite searching hard, i couldn't find a valid Lua C API example for calling a Lua function returning custom data from C function. id, row. If I simply do the So, when the function starts, lua_gettop(L) returns the number of arguments received by the function. Functions are often used as event handlers and for decisions which a library does local shallow_copy = function(tab) local rep_tab = {} for index, value in pairs(tab)do rep_tab[index] = value end return rep_tab end -- because local variable is not defined or declared immediately on a 1-liner, -- a declaration has to exist so that deep_copy can be used -- lets metatable execute functions local deep_copy deep_copy = function Warning. The way you describe (allowed in many languages) is actually a bit varags functions that return vargas lambdas lua. Functions can also return values back to the code that called them using the return keyword. How would I be able to move the contents of the if statement outside of the function A, while not changing any code inside of it? Effectively achieving the following result-- file A. 0. The unpack() and select() functions can be used to handle multiple return values. ``gettable'' called when Lua tries to index a non table value. To return values to Lua, a C function just pushes them onto the stack, in direct order (the first result is pushed first), and returns the number of results. ---@return Car|Ship local function create () end---Here car_or_ship doesn't need @type annotation, EmmyLua has already inferred the type via "create" function local car_or_ship = create 1 2 3 4---@return Car function factory: create () end. This returncode is what the os. function sumOfTwoFunctions(firstFunction, secondFunction, input) return firstFunction(input) + secondFunction(input) end The above sumOfTwoFunctions function shows how functions can be passed around within arguments, and accessed by another name. table_ret. Lua - Can I pick the specific result(s) I want from a function that returns multiple results. The second assignment creates a different function value and assigns it Ahh, thanks, that's a really helpful semantic of 'chunk'. Functions can both carry out a specific task (what is sometimes called procedure or subroutine In Lua, you can easily return multiple values from a function by separating them with commas. In Lua, you can receive a list returned from a function using table. It is used to return a value from a function. underestimated feature of lua functions that is very powerful among developersJoin our discord server to join our small friendly community full of talented a In Lua, functions are first-class values. 'c' means call your hook function any time a function is called in lua, 'r' means call your hook function every time a function returns in lua, and 'l' means call your hook function whenever lua processes a new line of code. Lua Table Function returning. For the return statement, it's because otherwise it may be ambiguous: return f(1,2,3) Is this a return with no values or a tail call to f? after a quick look at the documentation here I don't imidiately see a mechanisms to return data from query. It can also have any number of return statements, and they need not return lists of the same length or meaning. a already installed on your system. Not even the message There's nothing. lua. The fourth edition targets Lua 5. Dynamic reference to Lua table method, param passed in is null. Accessing return values of Lua-functions in C++ and vice versa. C++ Lua Getting Value From Lua Table. Lua function not returning the values. Info: The you see is lua's syntax for variable arguments (these are packed into a table and used as the last argument to the function), and the unpack function takes a table and multi-returns a series of values. tb. The first argument (if any) is at index 1 and its last argument is at index lua_gettop(L). pack:. The interpreter returns the termination status of its child. values = {1, 1, 2, 2, 3, 3} Is it possible to dynamically 'unpack' (I'm not sure if this is the right term) these values in the function call? Something like. if 0 == os. These are 2 different syntaxes for the . First example -- how not to do it -- does not work because "fx" is not in scope inside fx, as intuition suggests (to me) it would not be. Lua includes several ways to include other code so that you could put your functions in one file then include it into the main program to make the code cleaner, or include other libraries of functions which may aid with whatever you’re doing. a, b = values print (a) print (b) If you only want a subset of the returned values, use the blank identifier _. The unpack() and select() functions can be Return − In Lua, it is possible to return multiple values by following the return keyword with the comma separated return values. Lua doesn't check the value stored in the func variable when compiling, instead Lua will look it up every time the call is made. In Lua, functions are "first-class citizens". Another Tip for getting the return code of a function is the Lua reference. 1 – Date and Time. Follow answered Oct 19, 2010 at 17:37. Use the string. For example, the following is perfectly In the Lua wiki I found a way to define default values for missing arguments: function myfunction(a,b,c) b = b or 7 c = c or 5 print (a,b,c) end Is that the only way? (value, default_value) if value == nil then return default_value end return value end variables by default equal with nil. function object:method(arg1, arg2) is same as function object. Constructions based on functions are easier to translate between different languages. wrap(function() val = {meta()} print ("--- So, when the function starts, lua_gettop(L) returns the number of arguments received by the function. Stack Overflow for Teams Where developers & technologists share private knowledge with coworkers; Advertising & Talent Reach devs & technologists worldwide about your product, service or employer brand; OverflowAI GenAI features for Teams; OverflowAPI Train & fine-tune LLMs; Labs The future of collective knowledge sharing; About the company Stack Overflow for Teams Where developers & technologists share private knowledge with coworkers; Advertising & Talent Reach devs & technologists worldwide about your product, service or employer brand; OverflowAI GenAI features for Teams; OverflowAPI Train & fine-tune LLMs; Labs The future of collective knowledge sharing; About the company Lua does allow you to define nested functions, but I can only think of two reasons to use them: to return a function that encapsulates a task, usually with some of the wrapper function's args and/or locals as upvalues. So returning the correct number of results is not a problem anymore, because calling lua_gettop() after lua_pcall() executed, will give you always the The code block below is an example of a simple Lua function. :. 2 When the initial argument is a number N, all additional arguments starting from the Nth are returned. An example of C code calling a Lua function is shown in Section 7. lua の実行結果は: [wtopia lua. While still largely relevant for later versions, there are some differences. Lua : return table trough function is nil. e: I have the string x = "foo", is it possible to do x()? If yes what is the syntax ? "looking for '". Lua - Can a function be called from a table value and its value returned. Lua: Read table parameter from c function call. In fact while ModuleScripts are frequently used to return a single table value they can also be used to return a single value of any type (that includes but is not limited to a function value itself). Lua functions can return multiple results : a, b, c = unpack({'one', 'two', 'three'}) If I'm not interested in the third return value, I can choose to ignore it when calling the function : a, b = unpack({'one', 'two', 'three'}) Is there a similar way to ignore the X first elements when calling the function ? Upon successful return, pclose() shall return the termination status of the command language interpreter. The "return" statement is used to return from a function. If a function returns multiple results, the first result is pushed first; so Lua return from function problem. 3. Since Lua discards unassigned values, this can be used to select a single argument: y = select(2, foo()) OP example function returns two values, but for functions that return more than two values: y, z = select(2, bar()) and _, y, z = bar() 28 The Lua-C API Functions are constructs found in most languages, wich compatible basic semantics. I would like to know how to get multiple return values from function in Lua C API. In most languages, functions always return one value. Is it possible in lua to execute a function from a string representing its name? i. lua and then assign and use fields from that table in your main file. This function returns two number results. This looks like function() end. how to play with a function which return table in lua? 3. Lua: Can Return statements be used in a ternary conditional statement? 6. f= tb. insert(), aren't relevant because these functions aren't supposed to return anything. Learn about return values in Lua programming. Lua C API: Retrieve values from Lua function returning a table in C code. lua function A() local x = 1 local y = 2 if then require("B. local function plus (a, b) lua requires explicit returns, i. See examples, syntax, and exceptions for these statements. But Lua doesn't do this right (io. This is Python code, not Lua code. 4. 完成指定的任务，这种情况下函数 This method can also be done using table. That left me wondering why there was no return value. Records end)(base. I've had related problems with documentation for Lua libraries written in C where Doxygen is no help at all since all Lua-callable functions have the same opaque signature. A unique feature of Lua is the fact Learn how to use the return keyword to return multiple values from Lua functions, and how to handle them in different contexts. There are certain cases where we want to return a value from a given function so that we can use it later. v. Let’s go over the basic string operations first. 3. Like a Lua function, a C function called by Lua The point is that if we substitute 'rejected:empty()' to 'true' then the function 'testrejectedArray' will return true So the function return false? But if we substitute 'rejected:empty()' to 'false' it's don't prints 'yey' So 'rejected:empty()' return true, but for a reason it won't return me anything. Once the module table is popped by lua_setglobal, the file Lua allows functions to return multiple values, which can be particularly useful. Actually, one of the versions I've tried so far was similar, only that I my first call was lua_pcall(L, 0, 0), which discarded the result. I'm writing a function for Nodemcu (esp8266) Lua to build command strings from UART (someone typing). new("W") t= tb. It is also possible to have an function as an expression, but then you can't give it a name (in the same way). The following function getTank() works (if not used as a function to print fluidName for example). These return values make use of a return keyword which in turn allows Unlock the power of lua return and master function outputs effortlessly. For instance, you can write an application to plot the graph of a function and use Lua to define the functions to be plotted. Lua function return. readHiResTimerFrequency(); --stores the tickFrequency --call this before code that is being 4. gmatch() or string. There are two possible reasons. In Lua, function definitions are assignments; as such, they are made at runtime, not at compile time. If you are splitting a string in Lua, you should try the string. Here’s a local function that takes two numbers and returns their sum. In this article, we’ll dive deep into Lua functions, discussing their syntax, parameters, return values, and best practices for using them. Lua - How to pass object's function as parameter to another function. Lua Function with Multiple Return Values. Commented Aug 30, 2013 at 0:04 @Mud: The examples you give, print() and table. function multiply (x, y) return x*y end local returnedValue = multiply(5, 4) print (returnedValue) 20. Stack Overflow for Teams Where developers & technologists share private knowledge with coworkers; Advertising & Talent Reach devs & technologists worldwide about your product, service or employer brand; OverflowAI GenAI features for Teams; OverflowAPI Train & fine-tune LLMs; Labs The future of collective knowledge sharing; About the company To be honest, there is no such thing as a named function in Lua. The table constructor {} will copy the values to be inserted, reading the variable myfunc and storing it under index [3]. print (returnedValue) I will give another example. sethook can handle 3 different characters in the second parameter so you can let it know when to notify you. Lua functions can be quite generous, handing back one or more values with a simple return statement. From what I have googled and found, some people prefer early return because it in a way validates the values passed into the function first, and then it gets that out of the way from the code. Part. 3 require lua function test1(x) local x=x return x end function test2(x) return x end Say I'm calling them like test(5). Another thing is if you should do the same thing with loops. lua function f (n) return (n), (n * 2), (n * 3) end for i in pairs ({f (2)}) do print (i) end. function getNameAndAge () return "John Doe", 30 end name, age = getNameAndAge () print (name, age) -- Output: John Doe 30 25. close always returns true). new basically just creates a new table and returns it, so in this code:. lua post hooking a function. See examples of multiple assignments, function calls, table Functions in Lua can return multiple results. local function my_fun(x) return nil, error("oops", 2) end local res, err = my_fun("foo") print(res) print(err) print("finish Yes: function a() -- do stuff if time_to_exit then return end -- do more stuff end The time_to_exit can be anything you want: check if something has become true or non-nil or check that time has elapsed, etc. Peter Smith Peter Smith. ; Edit: I use lua 5. Returning multiple values from functions in lua. Functions in Lua can return multiple values. To return values, a C function just pushes them onto the stack, in direct order; see Section 5. how to get the second return value of a function in a if condition in Lua? Hot Network Questions Lua function return string with C++. return expects a list of zero or more return values. Hot Network Questions Note that the Split function in Lua returns an iterator, not a table, so we print the function itself. You simply summon the function I would like to know how to get multiple return values from function in Lua C API. If the substring is not found, the function returns nil. name, row. When calling a function, to save these values, you must use the following syntax: Which will result in a = b = c = 5 in return is used to indicate the result of a function. Discover how to use multiple return values, handle optional returns, and implement common patterns for efficient function design. All the function/method calls print the same string "hello user". return several parameter from lua C function. Like a Lua function, a C function called by Lua can also return many results. -- The function signature in Lua doesn't specify return types,-- but we can return multiple values simply by listing them. To learn more about handling return values, visit the Lua Return Values guide. return result. foo = function (x,y) return x + y end Lib. Hot Network Questions Calling lua function that returns table. arrSimpleConv= (function(result,base)if not base then return nil end for rec in (function(rst) if not rst then return pairs({}) end rst:Sort{{field=5,descent=true},{field=7},{field=10}} return rst. To use it, you would typically use it in a for loop: for word in string. This means we can treat them just like any other value – we can assign them to variables, pass them as arguments to other functions, and even return them from functions! I have a simple lua code looks like below. そして, テーブルから可変 You see, it doesn't matter if the value exists or not when you compile new function. - You get more knowledgable with Lua through more experience]]--[[hookfunction. In Lua, a function can return a list of zero or more values. read_data[2]) but since the number of elements in the array is variable, I A function always returns a list of values. Basically, a fallback is a programmer defined function which is called whenever Lua does not know how to proceed. To quote from the Lua manual: If the last field in the list has the form exp and the expression is a function call or a vararg expression, then all values returned by this expression enter the list consecutively (see §3. How can I reinvent myself? This returns the value to where the function was called and ends the function. 6 Multiple return values in Lua. return z. cpath = ". find() function is used to search for a substring within a string and returns the start and end indices of the first occurrence of the substring. How to add function output to a variable using luasql. But what is happening when I return x? 在Lua中, return的用法比较"诡异", 为什么这么说呢, 因为它只能用在block结束的地方, 不能用在block的一个中间部分. lua file is: Note that if you don't need to store a Lua function "for use later" you don't need any of this: if your C function has some Lua function passed to it via argument you can call it outright. Here is the syntax: function simpleReturn() return 1, 2, 3 end In Lua, functions can return multiple values. sub() method if you know the index you wish to split the string at, or use the string. How to make the function check the if the words are present or missing in the string and print the messages correctly? Probably I didn't explain myself well enough. 4 reference manual section on Chunks : Lua 5. goo = function (x,y) return x - y end Of Example of Function with Return Value in Lua. 22. It might work in certain, specific cases, where you: a) happen to have a Lua parser around. Getting variable from a function. Vararg (``) function parameters don't work with `arg` variable. function getCoordinates() return 10, 20 end x, y = getCoordinates() print("X: " . type(f) end f=f[v] end if type(f) == "function" then return f else return nil, "expected function, not ". Here’s how to do it: function getCoordinates() return 10, 20 end x, y = getCoordinates() In this example, getCoordinates returns two values that can be assigned to multiple variables simultaneously. Make a local copy of the function-library. Lua table of string values as parameter in C function. The values are the results of expressions in the return statement. 完成指定的任务，这种情况下函数 One advantage to writing functions that return values in a language like Lua is that functions themselves are values that can be passed to and from other functions. A quick-and-dirty way to test l_sin is to I have a simple lua code looks like below. If object does not have a metatable, returns nil. it won’t automatically return the value of the last expression. Passing Parameter to a function in an table in Lua. Do NOT save the return type of a unsafe_function_result (function_result when safety configurations are not turned on) with auto, as in auto numwoof = woof(20);, and do NOT store it anywhere. tb. To create such functions in Lua, we only have to put together the regular syntax for functions and for tables: Lib = {} Lib. total = product (2, 4) Learn Lua Learn the basics of Lua, a general-purpose programming language used for building games, web apps, and developer tools. A function can return any length list. local z = x * y. In this way, it is possible to write functions that work with a variable number of parameters. local function getListFromDatabase() local select_stmt = db:prepare("SELECT * FROM list") for row in select_stmt:nrows() do print(row. You need to call that function and assign the returned value: grades_copy_table = returntable() When you return a value from a function, that value then becomes local to the scope in which you call it. As we mentioned earlier, Lua is Unicode agnostic. For example, I have register function "GetMyVector" and then I'm calling that from lua to retrive informations from C, what I got is a table but what I want is something like access to access variable from struct like in C, for 1. pack(func1()) print(t[1], t[2], t[3], t[4]) by using table. function add (a, b) return a + b end-- Call the function and store the result local sum = add (5, 3) print (sum) -- Output: 8. 2 – Calling Lua Functions. This is a simple HTML page containing a text <input> Lua Functions. A common mistake is to assume that loadfile (or loadstring) defines functions. So, the function's documentation is essential. "' expected table, not ". Lua functions can also return multiple values. Unlike its counterpart protected_function_result, function_result is NOT safe to store as it assumes that its return types are still at the top of the stack and when its destructor is called It defines a local reference c to the return value of the function call. Add a comment | 12 Lua 5. local function my_fun(x) return nil, error("oops", 2) end local res, err = my_fun("foo") print(res) print(err) print("finish This method can also be done using table. Remove the first local if you want the Learn how to use break and return to jump out from loops or functions in Lua. So returning the correct number of results is not a problem anymore, because calling lua_gettop() after lua_pcall() executed, will give you always the This will feed the double function, the half function, and the integer 4 into our own function. ) When called with a table, it returns the number representing the date and time described by the table. gmatch() if you will parse the string to find the location to split the string at. Like: do local abc = 123 dofile "somecode. @EgorSkriptunoff: The fact is that your suggestion doesn't work. Think of a function like a request or a question. This can be useful in various situations where you need to return more than one Lua's way is to allow a function to return multiple values and this in turn can be used to update any parameter by simply returning the modified value, and re-assigning it (from outside the function) to the needed variable(s). The only important thing during compilation is the variable's visibility. find() function: string. BrickColor = BrickColor. I haven't dug into these threads but some people are complaining about this brain damage. The result is 'attempt to concatenate string and nil' at the lines: mon2. Giving an expression a name in Lua in Lua Function Multiple Return Values, Print(returnvalue) Results in Attempt to Concatenate String and Nil. The other types are passed by value. 2 has the table. 4 return several parameter from lua C function. If a function call is used as a statement (see §3. sbk sbk. sub() methods. grades_copy_table = returntable Here you are assigning grades_copy_table the function returntable itself, not its return value. Defining a function within a loop using loadstring with Lua 5. This function then overwrites the existing text and returns the result from the "old" function. add has two parameters and assumes both of them have an s Luadoc is, um, quirky for sure. function name() end is a statement in Lua because it assigns the function to the global variable name. function testReturn return "This is a test!" end local returnedValue = testReturn ---- We've called the function, necessary for the functions to work. I'm trying to call a function in Lua that accepts multiple 'number' arguments. print) the ability to log when a common function is called, with an indication of where it was called from. This is a powerful feature that sets Lua apart from many other programming languages. f = function () return 1 end f = function (N) if N == 42 then return f() else return 2 end end print(f(42)) The first assignment creates a function value and assigns it to f. function product (number1, number2) result = number1 * number2. This function, Parameters are variables that act as placeholders for the values passed to the function. Lua-Reference/Tutorial Despite searching hard, i couldn't find a valid Lua C API example for calling a Lua function returning custom data from C function. In Lua, we typically represent iterators by functions: Each time we call that function, it returns a "next" element from the collection. What are the differences behind the scenes on what's going on with the return value here? Any usage of x in the codeblock follows the rules of local, I get that much. local a, b = vals print (a) print (b)-- If you only want a subset of the returned values,-- you can simply omit the When called with a number larger than the actual number of arguments, this function returns LUA_NOOBJECT. lua local function doSomething() -- do something useful here end local function doMore() -- do something else useful end return { doSomething = doSomething, The table3 example doesn't do what you think it does. Return multiple values to a function, and access them separately in Lua? 1. Lua - calling a function with more params that defined. There is an implicit return at the end of any function, so you do not need to use one if your function Functions can also return values back to the code that called them using the return keyword. All the Lua library function that don't return a value (e. Return multiple values to a function, and access them separately in Lua? 2. Lua: How to assigned a return value from a function to a local value of a different function in lua. The "break" statement is used exclusively to break out of a loop. For the return statement, it's because otherwise it may be ambiguous: return f(1,2,3) Is this a return with no values or a tail call to f? The select function in Lua is used to return the number of arguments that are passed into it as an argument. . lua")() end end -- file B. find(fullString, searchString, init, pattern) To quote one of the Lua authors in an e-mail on the Lua mailing list:. Share. The function correctly prints all the items inside getSData, but when it's time to return it doesn't return anything, and even dumps the whole table in the last print function. _, c = values print (c) I initialized the table and filled with random data, which is correctly returned. How do I return multiple values in a function return in lua. Lua return custom data from C function. Functions are an essential concept in programming. LUA table with function arguments and passing nil. Or as some people like to put it; all types are passed by value, but function, table, userdata and thread are reference types. The opposite is true when passing functions as parameters, anonymous functions are mostly used, and normal functions aren't used as often. This old value can be used for chaining fallbacks. A function can have zero or more return statements, each of which returns a list of zero or more values. Conceptually Calling lua function that returns table. 2. This is can be helpful to preserve a simple check of the number of results using the length operator #; however it comes at the cost of no longer preserving the result "order". Green() or BrickColor. Lua files or strings are called "chunks" and are basically functions and may thus contain return statements like any other function. This function takes two arguments. Syntax. That's why Lua said it was expecting (after function. 2 "attempt to index global 'f' (a function value)" when trying to attach a function to the result of loadfile. 4. Closures are valuable also in a quite different context. This function returns a lua_Object, which is the old fallback value, or nil on fail (invalid fallback name). 25 Returning multiple values from functions in lua. so" --assuming Timer. gmatch ("a-b-c-d-e", "[^-]+") do print (word) end. The . For simplicity let's just note time: Lua return from function problem. A great strength of Lua is that a configuration file can define functions to be called by the application. Assigning and Passing Functions. If the echo programm exit with success it will return 0. how to play with a function which return table in lua? 5. But it is. If a function returns multiple results, the first result is pushed first; so Calling lua function that returns table. lua 1 2 3. Because functions are stored in regular variables, we can easily redefine functions in Lua, even predefined functions. The details really depend on what you want to achieve (if you need more detail, clarify your post and post a comment to this answer so I know). For definition it is exactly the same as specifying self manually - it will even produce same bytecode on compilation. This is fundamentally because functions in Lua do not carry any information about their origin. You see, it doesn't matter if the value exists or not when you compile new function. If the stg string has none of the matching words, the function returns nothing. Frankly, I don't know how to precisely describe varags functions that return vargas lambdas lua. Its return value is the final result of the indexing operation. You can achieve in a similar way. 2. 6), then its return list is adjusted to zero elements, thus discarding all returned values. Lua return from function problem. If a function ends without executing a return statement, it returns a list of no values. – Mud. For Stack Overflow for Teams Where developers & technologists share private knowledge with coworkers; Advertising & Talent Reach devs & technologists worldwide about your product, service or employer brand; OverflowAI GenAI features for Teams; OverflowAPI Train & fine-tune LLMs; Labs The future of collective knowledge sharing; About the company Probably I didn't explain myself well enough. __add when it sees f+t and passes both operands as arguments. For example, I should be able to say. sin(x)+math. We have already seen several examples of functions in table fields: Most Lua libraries use this mechanism (e. Any other value in the stack below the results will be properly discarded by Lua. Then you can have this library in a shared format like that: To return values to Lua, a C function just pushes them onto the stack, in direct order (the first result is pushed first), and returns in C the number of results. I. execute() function get and returned too. This is documented in the Lua 5. array_of_awesome_data = table. function addNumbers (num1, num2) return num1 + num2. The problem is a different one: your variables in get_poll_params are declared local inside the if/else blocks, so by the time you get to return they are all out of scope, so your code is equivalent to return nil, nil, nil. For example, I have register function "GetMyVector" and then I'm calling that from lua to retrive informations from C, what I got is a table but what I want is something like access to access variable from struct like in C, for This assumes all the functions in the table have more or less the same arguments. , tables do not inherently own the functions that they store. Lua's function, table, userdata and thread (coroutine) types are passed by reference. This concise guide simplifies the concept with clear examples and tips. A return statement returns occasional results from a function or simply finishes a function. Lua Getting Result Back in LuaJava from Lua function call. Here's an example showing off multiple return values: Output: In Lua, you can craft nameless wonders with the In this article, we'll dive deep into Lua functions, discussing their syntax, parameters, return values, and best practices for using them. Following is the source code for a function called max (). (It returns also the Let’s get into the string operations in Lua. So the luaopen_* function starts with those two values on the stack. 3 and is available at Amazon and other bookstores. Closures provide an excellent mechanism for that task. onData but you could try referencing an upvalue that is in SearchDatabase from your anonymous function. 0 Getting variable from a function. 3 Reference Manual 3. (In most systems, that number is the number of seconds since some epoch. 7. Unicode agnostic is good enough for most things, but there are situations where this just doesn’t work, so we’ll introduce a library for working with utf8 in Lua as well. hajime]$ lua table_ret. This function does some post-processing, after referenced function returns. function(a, b) return a + b end defines a function value with two parameters a and b that when called returns the sum of a and b. 6 Function Definitions. pack you can discard nil results. In Lua, functions are recognised as first class values. We do this magic with lua_pushcfunction: It gets a pointer to a C function and creates a value of type "function" to represent this function inside Lua. For that, you can go here to download the source code of your favorite version of lua and tweak the Makefile in the src folder to create a liblua. Multiple return values can be passed to another function by grouping them with parentheses. I want to use my c++ class member function in lua , but lua_register() function's 3rd parameter can only accept c type normal function pointer or static member function's pointer. Lua Code: function test(a, b) return a, b -- I would like to get these values in C++ end C++ Code: (part wher The function declaration is creating a new local variable that is nil unless an argument is actually passed into the function, but the timer function that calls your anonymous function isn't expecting to pass anything in, so the function-local n stays nil. Functions are central in Lua. 例如 function a() i = 1 return i -- 这里会报错, 提示return后面必须是end, 意思是既然你要return了, 那么就结束这个块吧. Functions in Lua can be defined anywhere in the global level of a chunk. I would like to create a function (call it fcreate) that when given a string, returns a Lua function. foo. c) are not embedding Lua in an application. local func func = function ( n ) if n == 1 then return Lua 函数 在Lua中，函数是对语句和表达式进行抽象的主要方法。既可以用来处理一些特殊的工作，也可以用来计算一些值。 Lua 提供了许多的内建函数，你可以很方便的在程序中调用它们，如print()函数可以将传入的参数打印在控制台上。 Lua 函数主要有两种用途： 1. Lua offers a wide range of functions for working with text. sin). To explain further, if func1 instead returned 1, nil, 1, 1 What I need is pass a specific value to a function, "elaborate" it, and then assign another local function to be elaborated later, let's make a simple example: local function test(x) local z=x return z end local x=1 test(x) print(z) So, 'x' debug. function checkMath(equation) if equation == 4 then return true end return false end workspace. See load as an example. so and place it next to the liblua. x . All functions are actually anonymous, but can be stored in variables (which have a name). end. – all done with standard mechanisms for tables and functions. so i know you can do stuff like this in lua to kind of shorten your code so you don't have to make unnecessary if statements . Modules, OO programming, and iterators need no extra features in the Lua-C API. To compile this project into a shared library, you must also have a shared library of lua itself. How use function value on table in lua. This statement returns true or false. 4 Expressions. return a + b end Lua Function Multiple Return Values, Print(returnvalue) Results in Attempt to Concatenate String and Nil. I'm trying to return all values within an array using Lua. Lua does allow you to define nested functions, but I can only think of two reasons to use them: to return a function that encapsulates a task, usually with some of the wrapper function's args and/or locals as upvalues. The metamethod is looked up in func. Multiple return values can be captured using multiple assignment or stored in a table. icon) end end Actually, I am new to lua programing I want to return a list of records, I am not getting I want to load some lua file, and then paste it into middle of my code. Lua: problems when using parameters to reference table values. Hot Network Questions Can Christian Saudi Nationals visit Mecca? there is a subscript bug in beamer Largest number possible with +, -, ÷ How to access the return value of a C function called by lua_pcall? 0. In my view, this is a 'cleaner' way of doing things. Operate(10, 42, function(a, b) return a + b end) where. There is a special syntax for definition of methods I want to return the list of records from retrieving data from database in lua program. Their arguments are accessible through the vararg . Notice how you can still call a method (a function which has its container table as the first argument) the same way as a normal function, but you have to explicitly pass the table as the first argument. Lua - Passing a function with some arguments already filled. insert, etc. Here is other example of it: local function GetSquareRoot(x) if x < 0 then return end -- Stops the function return x ^ (1/2) end Note that once the return keyword is executed then the code inside that function after the return is wrote wont be executed Basic Function Syntax; Function Parameters; Return Values; Anonymous Functions; Recursive Functions; Basic Function Syntax In Lua, whipping up a function is as easy as pie. It will not create the myfunc entry to be filled later. function addShape(x1, y1, x2, y2 xn, yn) and I have a table of values which I'd like to pass as arguments. Lua 函数 在Lua中，函数是对语句和表达式进行抽象的主要方法。既可以用来处理一些特殊的工作，也可以用来计算一些值。 Lua 提供了许多的内建函数，你可以很方便的在程序中调用它们，如print()函数可以将传入的参数打印在控制台上。 Lua 函数主要有两种用途： 1. It is not required if the function returns naturally; It does not require a return value; The "goto" statement jumps execution to a "label" The syntax of the "goto" and "label" are given below how can one get the caller of function within a function in lua? Specifically I'm looking (for debug purposes in the command output, e. You can check by adding for i = 1, v. return function() return "abc", 123 end bar. cos(x)") print(f(2)) -- evaluates sin(2)+cos(2) print(f(3)) -- evaluates sin(3)+cos(3) To make things easy, the string will just be a function of x. write(returnedVariable) for example which is outside of the function. I. 有参数的函数格式----多传了参数会丢弃，少传了参数会 The pairs function, which iterates over all elements in a table, is similar, except that the iterator function is the next function, which is a primitive function in Lua: function pairs (t) return next, t, nil end The call next(t, k), where k is a key of the table t, returns a next key in the table, in an arbitrary order. Why? Hot Network Questions. How can I reinvent myself? I would like to create a function (call it fcreate) that when given a string, returns a Lua function. something like result then you set result = d[value] in your anonymous and then return result from SearchDatabase – Nifim The table has 3 functions (a,b and c) and a string entry under the key greeting. Calling lua function that returns table. RecordSet) do This can go horribly wrong with metatables, especially since you're setting the metatable first and then assigning the fields (__newindex could do all sorts of funny things). lua return function B() x += 1 y += 1 end Lua does not have reflection, but the function names are stored as string in memory as a "key". lua (Syntax): Calling a function that returns more than 1 value, and using those values as arguments, but without extra lines of variable assignment? To redefine a function within the function itself, you need a reference to the function in a variable that has already been declared before the variable is assigned a reference to the function. (If the loader came from a file, this extra value is the file name. 6. Number of returned values. 2 Unable to get C function return value from Lua function. 10). In Lua, you can return multiple values from a function by separating them with commas, allowing you to effectively pass back multiple results in a single call. Sorry if this is a dumb question, I'm a fairly inexperienced programmer. I can return individual elements by calling their index (ex. read, math. Get Lua string from C. Workaround for error: "outside a vararg function near" 0. print, table. The syntax for function definition is: functionfunction var ( parlist1 ) block end If control reaches the end of a function without a return instruction, the function returns with no results. Modified 7 years, 3 months ago. In other words: function x() return 3 end function foo() local y = x() -- y is now local to the scope of foo() end. ; Edit: How can I return more than one level of callers in Lua? Something like in Forth when you drop one value from the stack of returns?. f=fcreate("math. A request could be asking for an object: "Can you bring me a glass of water?" Or it can simply be Functions are the main mechanism for abstraction of statements and expressions in Lua. so ----- package. so is in the same directory require "HighResolutionTimer" --load up the module timer. 6. このように, 可変引数をテーブルに変換する場合は, { 関数() } のように書くことができる. How to retrieve another variable within table in Lua? 1. Converting Python function to As egarcia said, if lua_pcall returns 0, the table the function returned can be found on top of the stack. Otherwise, if the object's metatable has a __metatable field, returns the associated value. Unable to get C function return value from Lua function. To explain further, if func1 instead returned 1, nil, 1, 1 This first edition was written for Lua 5. 1 in my c++ game project, but I had a trouble to use lua when I try to register a c++ member function. 2 Function that returns function based on expression text. Otherwise, returns the metatable of the given object. Lua doesn't make it easy to get good documentation signatures for functions, and most of luadoc's quirks relate to that. local a, b = require "foo" () Share. Lua Code: function test(a, b) return a, b -- I would like to get these values in C++ end C++ Code: (part wher angles = function() x = function() local value = 0 return value end y = function() local value = 90 return value end z = function() local value = 180 return value end return x(), y(), z() end A problem arises here when wanting to use, for example, the x value separately, while keeping it in the function angles . e. Before we can use this function from Lua, we must register it. On use : is almost the same as . You can either create a wrapper just for that function, or you can actually set a debugging hook in the Lua runtime. How to call a C Function from Lua with table type argument and table type return value? 5. g. You can see this if you write the loop like this: for i in coroutine. /Timer. In this context, a variable is an expression. We’ll learn about functions with a few different examples. The issue comes when I return the values and then try to access them outside of the function. 1. #!/bin/lua ----- ---HighResTimer. - a special kind of call will be used internally to make sure object and any possible side-effects of calculations/access are -- table_ret. This function value is provided as the third argument to Operate. n do print(i, v[i]) end to your sample code above. Moreover, both functions never have any kind of side effect. This happens GetCharacterName(source) is not the last in a list of expressions or if you put that function call into parenthesis or you assign it to a single variable. Follow answered Apr 14, 2013 at 13:08. There's two different things you can do. jvet cdbm vzexc lbnwax fpkjqqe hblg onhhs qdc nzkdj qnme
