Lua pcall return value. lua:2: in function 'add' main.

Lua pcall return value This And it should get the return value. Let's xpcall works the same way as pcall but it actually lets you control the error handler, means you can change the error message etc, by passing a second function argument as callback. If you check the documentation for lua_getglobal you'll find “Pushes onto the stack the value of the global”. How to properly use pcall() - Scripting Support - Roblox Loading When the return value of lua_pcall is not LUA_OK, (L, filename) || lua_pcall(L, 0, LUA_MULTRET, 0)) and is a convenient way to load and execute a chunk. As suggested in the comments, you can use local ok, res = xpcall(f, debug. That way you don't have to know anything about binding implementation. When you call luaL_loadstring it puts a callable chunk/function on the stack (the function represents your file). 4 Lua: no stack trace when calling error() without arguments? 7 Get all errors from lua_pcall(L, 0, 0, 0) The return value is a boolean true in case the current user has permissions to execute the command (via a call to redis. setlocal call into the same function (=same scope) so that I check and re-assign in one step! I have created a Lua table in C, but I'm not sure how to push that table onto the top of a stack so I can pass it to a Lua function. First, it's easier to help if you state the problem you're trying to solve. pcall()) in Lua as it would be returned if the command had been called directly. Avoiding use of global variables with specific callback mechanism in Lua. 2 function to get called from C++. lua_string = foo() This assumes you have already registered your function with lua_register How to return multiple values? - Scripting Support - Developer Forum Loading It attempts to compile and run (using load) a string which isn't valid Lua code. So remember, this lua_pcall() is lua_pcall(L, 1, 1, 0). Finally, I moved the debug. (Loaders are now called searchers in 5. From what I understand: A p (rotected)call () will not error, instead it provides you with two variables: Success and Error. return function () return fix_return_values(pcall (f, )) end end end. The function as_table creates a new table from a pair of iterators, from_table const char* answer = lua_tostring(LS, -1); lua_tostring returns a pointer to a string in Lua VM. ; You're calling lua_pop with a negative index but it expects a positive integer. Lua is a language with GC, so this string will disappear after you pop it from Lua API stack: lua_pop(LS, 1); You end up with a dangling pointer. pcall returns two values: A boolean indicating whether the call was successful (true) or if an error occurred (false). Then you can use require normally and just check its return value. Protected calls can be used for when a piece of code is It attempts to compile and run (using load) a string which isn't valid Lua code. Does anyone know how to do this? This is my current code: lua_createtable(state, libraries. Calling local function inside another local function. Why do you think it should succeed? – interjay. However, if there is any error, lua_pcall catches You call lua_pop() to remove items from the Lua stack. 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 when using strict mode, pcall only allows returning 1 value, for example: --!strict local function foo() end local success, response = pcall(foo) TypeError: Function only returns 1 value. ; Note, the reason you're currently getting 1 for When you call your Lua function, it returns its results as value on the Lua stack. Converting std::vector to and from Lua table. return value of the function As in a Lua assignment, lua_pcall adjusts the actual number of results to what you have asked for, pushing nils or discarding extra values as needed. By buying the book, you also help to support the Lua project. The default protocol version during script executions is RESP2. For simple functions, this can be entirely unnecessary since the core will clean up the stack as part of handling the return values. size(); i++) { lua_pushstring(state, libraries[i]. How can I apply an array formula to each value returned by another array formula? How we know that Newton and Leibniz discovered calculus independently? Why is the retreat 7. While Lua is running a hook, it disables other calls This first edition was written for Lua 5. After calling the index function, its returned values are put on the stack. pcall()) to Lua data types depends on the Redis Serialization Protocol version used by the script. Unable to get C function return value from Lua function. getlocal() because this introduced another stack level and thus returned wrong thread and index values that didn't work with debug. The fourth edition targets Lua 5. 2 end if key &gt;= max then return nil else return key+2, "val:" . I have an sql statement that could return a result or not. lua_getglobal(L, "f"); lua_call(L, 0, 1); // no arguments, one result Otherwise, the script as shown does create a global variable, and lua_getglobal() would retrieve that to the stack where it could be tested with lua_isstring(), or probably more usefully let you return its value if it is sufficiently string-like with lua_tostring(). Let's And im trying to pcall so i dont get errors but it returns nil even when its a name that i know works because i call for it regularly above. lua-l@lists. call('hgetall', ckid) return {ckid, meta} if the key does not exits for the first call I would not like to execute the second. This is my attempt (does not work, i This function is similar to pcall, except that it sets a new message but it extends stock Lua in several ways. key+2 end end if i As of right now StackExchange. Loads and runs the given string. call() (or redis. The result of the function call if successful, or the error message if an error occurred. Viewed 691 times Lua: How to properly clean up errors returned by lua_pcall. However, you can re-enter the yielded coroutine by again calling coroutine. and it returns the id in the print but when i try to pcall then use an if it comes back nil everytime and goes to my else statement. An example is the string. 0. If lua_pcall returns error, are there still return values left on the stack? Ask Question Asked 6 years, 5 months ago. As discussed in chat it might be desirable to convert the function arguments from std::vector<float> to Lua tables and the return value from Lua table to std::vector<float>. 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 This tells Lua that you expect a single return value, and if the user doesn't provide one, Lua will push a NIL onto the stack. function f() return 'some text' end local status, res = pcall(f) if pcall () succeeded, status is true and res is the return value of f (). This means that any error inside func is not propagated; instead, pcall () catches the error and returns a status code. Discussion: How do you return multiple values? Geoff number of return values of a>) would work, but I'd like to do better). If pcall successfully manages to function, then it will run Return Values: Returns two values. //typedef int(*data_callback_t)(int i); int test_callback(data_callback_t f) { Your use of lua_gettable is wrong. In this case that appears to be a table. Getting the returned values. Cheers, Geoff. e): {'value1'}; >> 'value1';-Change the k,v loop to a generic for loop (I believe that would be more efficient?). – Egor Skriptunoff Commented May 10, 2017 at 20:45 static int foo (lua_State *L) { int n = lua_gettop(L); //n is the number of arguments, use if needed lua_pushstring(L, str); //str is the const char* that points to your string return 1; //we are returning one value, the string } In Lua. In order to fully pass an integer into callfuncscript. The documentation says luaL_dostring does have a return value, which is zero on success: luaL_dostring. b = ({test()})[1] The same is true for the C API: both lua_call and lua_pcall are always provided with the expected number of return values (or LUA_MULTRET). It is defined as the following macro: (luaL_loadstring(L, str) || lua_pcall(L, 0, LUA_MULTRET, 0)) It returns 0 if there are no errors or 1 in case of errors. Leave the original returned value on Lua stack, or copy it into other Lua container (your Lua table for temporaries, or Lua registry), then copy that value on Lua stack to pass it as an argument. status (boolean) Returns true if the function was executed with no errors. 4. pcall() eval "return redis. There are a couple of issues above: You're trying to compute factorialLua(divLua) in the script before divLua is set from C++. But Lua doesn't do this right (io. We also check if the function lua_pcall returns LUA_OK to continue for a call that worked. The values returned will be retrieved from the stack. Follow edited Jul 4, 2023 at 6:14. Redis integer reply -> Lua number; Redis bulk reply -> Lua string; Redis multi bulk reply -> Lua table (may have other Redis data types nested) Redis status reply -> Lua table with a single ok field containing the status I'm unsure if your example was meant to be production code or not, but there are a few optimizations (although small) you could make:-Make the table a local variable (i. I'm allowing the script to omit functions that are attempted to be calle PCALL and XPCALL - Very useful How pcall and xpcall works by Isaque232 Otherwise, the script as shown does create a global variable, and lua_getglobal() would retrieve that to the stack where it could be tested with lua_isstring(), or probably more usefully let you return its value if it is sufficiently string-like with lua_tostring(). (specifically, I'm trying to remove duplicate strings, and some other things) I'm wondering if there is a way to set up so that I can still make these lua calls, but have the lua state remain open for the duration of the recursive operations. 1. The return value is a boolean true in case the current user has permissions to execute the command (via a call to redis. Checking their types are also important to make sure that they are the expected ones. 2k 6 6 I'm trying to get a value from a MySQL database query in lua, but cant seem to either return a value or set a local variable outside the callback either, the only progress I have made is being able to continuously pass the value through callbacks to where I need it but even then its still stuck in a callback and i'm unable to assign it to No. execute is a good idea. First value is true, second value is what was returned by the function (4, because 2*2 is 4) Use Cases. IMO that you need is dofile(lua_file_name): Opens the named file and executes its contents as a Lua chunk. The loop iterates at most 242 times (because of the limit on the number of arguments in function calls), or less (some Lua I've been having a crash problem with Lua for a little while now, and I finally discovered what I believe to be the problem. 26. Ok, dug deeper in the documentation, Redis nil does convert to false in Lua scripts: Redis to Lua conversion table. char to implicitly do the concat:. Redis doesn't have any higher-level API wrapping up the functions API, however, you can just use the ad-hoc command API pretty easily. Are you trying to prevent uninitialized globals from being used? You can do that with a metatable. time()) local "Just make sure there is at least one lua_pcall at the top or your app" This assumes that Lua is in charge of the application, rather than the application calling Lua to perform specific tasks. function f (v) return v + 2 end -- f a, b = pcall (f, 1) print (a, b) --> true 3 a, b = pcall (f, "a") print (a, b) --> false stdin:2: attempt to perform arithmetic on local `v' (a string value) If you are expecting to get multiple return values from the protected function, then the code below would let you do that: First, I removed the wrapping pcall() from debug. Improve this answer. The newtry factory. lua:2: attempt to perform arithmetic on local 'b' (a nil value) stack traceback: main. pcall a lua function return two number c++ calls the lua function: foo I don't know whether it's needful to pop the return value of function foo(lua_pop(L,2);). /* code 1 */ return k(L, lua_pcall(L, n, m, h), ctx); } In the above code, the new function k is a continuation function (with type lua_KFunction), which should do all the work that the original function was doing after calling lua_pcall. Share. lua. For return events, event can be LUA_HOOKRET, the normal value, or LUA_HOOKTAILRET. OnClientEvent:Connect(function() return Notebooks end) Server function IfDoorOpen(plar) I don't think that executing a Lua file using os. You can call the function with. If there are no errors during the call, lua_pcall behaves exactly like lua_call. randomseed(os. A great strength of Lua is that a configuration file can define functions to be called by the application. However, the results of one lua return can effect the results of a later lua return. This Below is my lua script: local ckid = redis. call or redis. How to access the return value of a C when using strict mode, pcall only allows returning 1 value, for example: --!strict local function foo() end local success, response = pcall(foo) TypeError: Function only returns 1 value. Thinking about performance, it might be advantageous for a Lua function to be able to determine the number of expected return values expressed by their callers, so as to avoid computing return values that the caller did not Let's edit the example to make it work & see how the values returned will change: local function foo return 2 * 2 end local success, msg = pcall (foo) print (success, msg) true 4. notify Lua: How do I execute a callback passed from a parameter? 0. 3 and is available at Amazon and other bookstores. I keep getting "attempt to index a nil value" in the if statement line. Introduction. resume(). When a return value is a table, retrieving the table's elements isn't obvious. So if you look at both return values, you can see if the string was valid Lua code before trying to call it. Can I know the count at . 3 on Debian 8. I'm having problems getting a Lua 5. This function pops the key from the stack (putting the resulting value in its place). Try changing the load call to this: local chunk <const>, Then it will capture the n variable from the outer scope, which has the value returned from hs. You can get string. 2 – Calling Lua Functions. Oka Oka. I do not have access to any module or the C side. Before pushing the results, lua_pcall Call the function with: lua_pcall(L, arguments_count, returnvalues_count) (you can return multiple values in Lua functions) The result is available on the Lua stock (top) Note: you need to push each function This tutorial covers calling a Lua function from C/C++. O’Reilly members experience books, live events, courses curated by job role, and more from O’Reilly and nearly 200 top publishers. if pcall () failed, status is false and res is the error message. The solution is to (1) localize everything and (2) use different names or (3) get rid of the inefficient string concatenation entirely. Thanks for contributing an answer to Stack Overflow! Please be sure to answer the question. In python the return value would be None. The state of the stack was this before issuing the function call: {return value} The lua_pcall will remove the argument(s) and function from the stack. That is the table you need to have require return as well. Provide details and share your research! But avoid . 2+ or LuaJIT (with Lua 5. pcall) the replies from redis. 2. Now let's talk about the stack. thank pcall(a, arg) Actually I am using 'lua_lock/lua_unlock' to protect the lua_State from corrupting. Modified 9 years, 6 months ago. Try changing the load call to this: local chunk <const>, err <const You're overwriting the global variable genRanHex that holds the function with the string genRanHex you're building in the function. The last 2 of them are not covered here as they are related to yielding which is an Return Values. It would work with proper shebang, but will spawn separate process(es). ; Assuming the first two points are addressed, you're trying to compute 125! which is going to be a really large number. pcall('get',KEYS[1]) local meta = redis. Robust code should check for 0 return value. setlocal(). For more complex functions, and especially for C code that is calling into Lua, you will often need to pop things from the stack to prevent the stack from growing indefinitely. I am running lua 5. SoI don't what the return value is for None. The interpreter returns the termination status of its child. I have a C function (A) test_callback accepting a pointer to a function(B) as the parameter and A will "callback" B. If it doesn't return a result I need to change the nil value to "none". If nargs is 0 you'll get the dreaded " attempt to call a number value" error, while if nreturns is 0 it will always return 0. Converts the Lua value at the given index to a C boolean value (0 or 1). . You may want to check this patch that extends pcall to include stacktrace. ) See Etan Reiser's answer if you want to support stock Lua 5. call(ARGV[2],KEYS[1])" 1 key get eval "return redis. How is that handled? /* code 1 */ return k(L, lua_pcall(L, n, m, h), ctx); } In the above code, the new function k is a continuation function (with type lua_KFunction), which should do all the work that the original function was doing after calling lua_pcall. The advantage of this is that it is completely transparent at the Lua end. I am trying to learn lua and I seem to be stuck here. 2k To return values to Lua, a C function just pushes them onto the stack, in direct order (the first result is pushed first), this is the size of the block of memory allocated for the userdata; for other values, it is 0. call() and redis. ) luaL_loadstring(L, "return 3, 4, 5"); int R = lua_pcall(L, 0, 3, 0); Lua can return multiple values. For example, I can pass and return values to/from Lua function in C++ like this. function f (a,b) return a + b end status, ret = xpcall (f, debug To get the value of any other field in ar, the hook must call lua_getinfo. lua:2: in function 'add' main. You can convert the multiple return values into an ordered table/array and then get the value for an index. This perpetuates disuse of exceptions and strengthens anti-exception patterns such as signaling errors by way of return values. math. Introduction Protected calls, formally known as pcalls, can run functions without erroring and provide if your code was successfully ran but what’s the best way to use them and when should I? In this tutorial I will be covering the entirety of pcalls and where you’ll need them, so lets begin! Pcall basics First and foremost, we should learn what pcall’s syntax really looks You can pass values out via coroutine. lua's square() function and receive the function's return, the lua_pcall()'s nargs argument must be 1 (one argument passed in) and its nreturns argument must be 1 (1 argument passed back). Asking for help, clarification, or responding to other answers. traceback, args) with Lua 5. Florian Weimer return b1(pcall(a)) end end. Permalink. But currently I have to hardcode the count of the return values. pcall) The last example demonstrates receiving and returning the exact return value of redis. When you lua_pcall that function you run the code in your file and it returns whatever the file returns. The correct way would be to pass the Lua value as it is. Also note that the recursive call to add() in the solution is a trailing call, so Lua compiles it as a loop: it iterates after reducing 2 arguments acc and [1] by the addition acc+, and shifting all other arguments in to the left, using select(2, ). Passing Tables to Lua Functions A use case that happens often is the passing of tables to and from Lua functions. For instance, you can write an application to plot the graph of a function and use Lua to define the functions to be plotted. Now, we The Lua value must be a string or a number; otherwise, the function returns NULL. 2 are req Several predefined functions in Lua return multiple values. Modified 6 years, 5 months ago. Lua possesses the necessary building blocks for exceptions; however, rough edges appear when one tries to assemble them. please tell me how to do it and why. A multiple assignment allows the program to get both results: Thanks for contributing an answer to Stack Overflow! Please be sure to answer the question. Here's how I would rewrite it, leveraging string. yield() by putting them as arguments into the yield() function call. org . e): local table = {};-Remove the unnecessary tables (i. What I'm trying to make is a function that receives, as parameters: a number that is an ammount of second; a callable value; By 'a callable value', I mean a value that can be called. 2 are req The reason I'm passing in a lua_State* parameter into the constructor is because I want the created object to store it as an attribute, so it can then use it to call lua functions itself. c_str()); lua_rawseti(state, table_index . If the function doesn't throw any errors, then lua_pcall will: Remove the parameters from the stack; Push the result to the stack; This means that, if your function doesn't throw any errors, you can use lua_setfield right away - lua_pcall will work just like lua_call: lua_pushstring (lua, "funcname"); lua_gettable (lua, LUA_GLOBALSINDEX); lua_pushstring(lua, The problem I was having was that I simply invoked lua_pcall(L, 0, 0, 0) and ignored the return value because it didn't matter to me. Its 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 I wonder if it is possible to dynamically find out the number of return values of Lua function in C++. 2 issue: 'attempt to call a nil value' from lua_pcall. Try input some code and press the EOF key (Ctrl + D in Unix or Ctrl + Z in Windows) – Yu Hao When the return value of lua_pcall is not LUA_OK, (L, filename) || lua_pcall(L, 0, LUA_MULTRET, 0)) and is a convenient way to load and execute a chunk. Additionally, I can not use the IO, the OS or the debug library. And form the source (lua 5. int main() { lua_State* L = luaL_newstate(); luaL_openlibs(L); function iter2(key,max) if key == nil then return 2 , "val:" . It returns two indices: the index of the character where the pattern match starts and the one where it ends (or nil if it cannot find the pattern). GET_NOTEBOOKNUMBER. Get Lua Quick Start Guide now with the O’Reilly learning platform. 25. In the latter case, Lua is simulating a return from a function that did a tail call; in this case, it is useless to call lua_getinfo. Ask Question Asked 11 years, 1 month ago. dump(func) and analyze the bytecode on number of values returned from this function (search for RETURN A B operation code, B=1 means no values returned). 2. To break the cycle, we first need to promote idioms and know-how for richer use of exceptions. It'll Fortunately, the pcall function will return two values! The first is a bool describing if the function was successful, and the second is either the value returned by the function or the error Calls the function func with the given arguments in protected mode. 2 compatibility turned on) and used a Your module returns a table. There are 4 functions responsible for that: lua_call(), lua_pcall(), lua_callk() and lua_pcallk(). answered Jul 3, 2023 at 17:33. I have put my code in pcall can still wont get overwritten. (If you want to accept only actual boolean values, use lua_isboolean to test the value's type. Like all tests in Lua, lua_toboolean returns true for any Lua value different from false and nil; otherwise it returns false. For some reason the following code doesn't actually run the lua file. ReplicatedStorage. I haven't dug into these threads but some people are complaining about this brain damage. resume() call instead of the normal return values. If you pass LUA_MULTRET this adjustment will not take place and you have to figure out the number of return values by comparing the result of lua_gettop() before and after the call. Viewed 5k times 6 . g. Returns all int lua_pcall (lua_State *L, int nargs, int nresults, int errfunc); Both nargs and nresults have the same meaning as in lua_call. You can pass the number of return values you want as the third argument to lua_pcall(), and Lua will adjust the real number of values to the requested number of values. close always returns true). I cant seem to figure out how to do this. Status So I want to make a remote event that returns a value from a localscript, heres what I have so far Client game. ) Note that this question is about pure Lua. void lua_gettable (lua_State *L, int index); Pushes onto the stack the value t[k], where t is the value at the given index and k is the value at the top of the stack. Returns false if an error occured inside the function. Example Usage. Geoff Leyland 2009-11-04 20:12:31 UTC. In the case of your function, it returns one value, so calling the function will return the table t on the top of the Lua stack. While still largely relevant for later versions, there are some differences. Assuming the Lua lua: main. 4) I can see 'lua_pcall' is calling 'lua_lock/lua_unlock', but I am not sure if normal way of function call is also based on 'lua_pcall' or using 'lua_lock/lua_unlock'? Let's edit the example to make it work & see how the values returned will change: local function foo return 2 * 2 end local success, msg = pcall (foo) print (success, msg) true 4. lua:5: in main chunk [C]: ? This is a runtime error, which had occurred due to not passing two variables. Protected calls can be used for when a piece of code is Upon successful return, pclose() shall return the termination status of the command language interpreter. Those values can be retrieved outside as return values of the coroutine. This first edition was written for Lua 5. size(), 0); int table_index = lua_gettop(state); for (int i = 0; i < libraries. I tried executing the below erroneous eval command to understand the difference between redis. Unfortunately Lua syntax requires that you wrap the array in a parentheses before using an access operator, so none of this will look very elegant. lua_pcall) or by explictly popping it with lua_pop. /* push fun Lua 5. int lua_pcall (lua_State * L, int nargs, int nresults, To make it more evident, we stick to a convenient standard (you probably already use anyways) for Lua function return values, and define two very simple helper functions (either in C or in Lua itself). Why do recent versions of Rust allow returning this temporary value? How does exposure time and ISO affect hue? What does a pcall actually return? - DevForum | Roblox Loading Instead of using pcall, you add can your own loader at the end of the list of loaders and make it so that your loader never fails but instead returns a special value, such as a string. 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 Thanks for contributing an answer to Stack Overflow! Please be sure to answer the question. find function, which locates a pattern in a string. How to fix: Copy string's content somewhere before popping Lua string from Lua API stack. @Samuel As I said in the answer, dofile(nil) executes the contents from the standard input, it doesn't return because it's still expecting input. Commented Aug 21, 2021 at 12:51. Have a look at the Lua manual:. You are responsible for removing it, either calling a function which implicitly pops it (e. fqn neh rvfje flgd vedj cyubky melhtr wpvd lpeh uibaa