gottfriedleibniz June 9, 2021, 9:04pm #2. If a Lua function returns n values, the first value is at location -n in the stack, and the last value is at position -1. You can rate examples to help us improve the quality of examples. Example. You can rate examples to help us improve the quality of examples. You can too return other values. 3. The Application Program Interface . When we use a call as an expression, Lua keeps only the first result. The counter_create function is the heart of the wrapper. Functions and Types. Lua is very loose about the number of arguments and return value, but C/C++ is less so -- hence we need to be explicit when calling lua from C/C++. An attempted fix was initially PRd in: fix (scripting/lua): support exported MRVs . Returns false if an error occured inside the function. Regarding your confusion in the comments of your code regarding the return value of luaL_dofile, it returns an integer status code.Most lua* functions that aren't retrieving a value return a status code indicating if everything went alright, or a vague idea of what went wrong. @gmail.com > wrote: The Auxiliary Library. Sorted by: 29. you could do something like this if you aren't sure how many values some function may return. NB: sending should be done with Lua pcall because results must always be intercepted. local ret1 = assert (task1 (arg1)) local ret2 = assert (task2 (arg2)) . They both allow multiple return values to be consumed by another function which takes the same values as arguments: func sum (x, y int) int { return x + y } This section describes the C API for Lua, that is, the set of C functions available to the host program to communicate with Lua. This function takes two parameters num1 and num2 and returns the maximum between the two Unless I'm missing something completely, that here is the main issue. Lua combines simple procedural syntax with powerful data description constructs based on associative arrays and extensible semantics. It seems that as of Lua 5.2 the return value isn't specified for tables where the set of integer indices has "holes . Each time counter_create is called a Lua state is created. . . Again, notice that the stack enables the transfer. Following is the source code for a function called max(). return a String to Print Expected Output Expand. The flag that allows a script to access keys from multiple slots. forget about having multiple Lua states, about binding CompCompiler in those states, about the LuaInstance singleton, zipped code, and so on. Following is the source code for a function called max(). Multiple return values - supported by both languages Strings are immutable in both languages C/C++ interfacing - Well developed in Lua . local f, err = io.open(filename) if err ~= nil then return "",err end. Sometimes you may want multiple values returned from a function. As well as private training courses on site, we run public Lua courses at our Melksham, Wiltshire, UK training centre. Call lua_pcall again, specifying the number of arguments and return values; Use lua_tointeger to get the return value from the top of the stack; . When we call a function as a statement, Lua discards all results from the function. Once the function has finished, the return values must be placed in the stack so Lua can reach them: // push to the stack the multiple return values lua_pushnumber(l, 12); lua_pushstring(l, "See you space cowboy"); The final part is to return the number of variables pushed to the stack that we want Lua to see as the C++ function return value: This data structure is a kind of unique session variable allowing multiple Lua scripting engine . This is intended to allow easy embedding into Go programs, with minimal fuss and bother. Load but don't run the Lua script file: luaL_loadfile(L, 'script.lua') Priming run of the loaded Lua script to create the script's global variables: Pass all arguments to the Lua script on the stack: Various routines, too many to name. lua_pcall fails (i.e. It's not a good idea to only skim through the comments before you press the submit button. Granted, Wc3 natives never have multiple return values, but this would extend the scope of application to user-written functions. function test () return 1, 2 end function test2 () return test () end function test3 () local values = {test2 ()} table.insert (values, 3) return unpack (values) end print (test3 ()) this outputs: DCLua - Go Lua Compiler and VM: This is a Lua 5.3 VM and compiler written in Go. This function takes two parameters num1 and num2 and returns the maximum between the two Use a comma to separate them. Basically, when I call lua_pcall, I want it to execute, finish executing (including any external calls it might have) and only then return control to the calling thread. An in-game example would be returning how many wins, losses, and ties, a player has. 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 argument separatly to the Lua stack. They would just be treated as arrays in the C# and JS script runtimes. These are the top rated real world C++ (Cpp) examples of lua_pcall extracted from open source projects. Example. The first argument is a string that consists of the script's Lua source code. The caller can expect any number of values returned: . The /usr/bin/luajit binary is a simple C frontend to libluajit-5.1.so: it provides a REPL (read-eval-print loop) and can also run a Lua script file if we pass one as an argument. (If there was a result set) Copy the result set to sqlresult. Below the function, use print () to call the new function. (2) getting Lua values on Lua stack. BuildingRobloxUnited (BuildingRobloxUnited) August 18, 2021, . This is useful if you want to run a test in a function callback, or if you want to write your own helper assertion functions. Lua can return multiple values so both the "fast" and "slow" functions return its own counter and the counter for the other function. lua_pop(L, 1); /* pop returned value */ debugging2 = stackDump(instEnum);} . . (This is the same as Lua's behavior on multiple assignment operations.) You have to register before you can post. It supports procedural programming, object-oriented programming, functional programming, data-driven programming, and data description. There are four basic interactions with the Lua world that you can see here: (1) is calling Lua to execute a chunk of code. You can pass multiple Lua files to the testy.lua script, or you can pass the -r command line flag, which causes testy.lua to also collect test functions from require d Lua modules recursively. ) Return Values: Returns two values status (boolean) Returns true if the function was executed with no errors. 3 Answers. /* 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. One way to do this in Lua is to set a global variable and then refer to that . You would think that lua_call would have equal (or mostly negligible) performance to lua_pcall if you set all the continuation and error-checking arguments to be their null types. Each time that the function lua_newstate() is called, the return value will be a pointer to a lua_State data structure or a NULL pointer if the call fails for some reason. The script doesn't need to include any definitions of Lua function. The files under /usr/share/luajit-2../jit are part of LuaJIT's jit library, which provides a Lua API to the JIT compiler. Both function calls and vararg expressions can result in multiple values. local function getWinRate() local wins = 4. local losses = 0. It is also possible to ignore returned values by using the throwaway variable _ in the . I believe you meant you can return any value of any datatype. end ) The Lua . Functions return multiple values: return 1, 2, 3. Well, it is a pretty simple way of getting return values, and there certainly are better ways. Create a custom function with variables for wins, losses, and ties. You might also consider to support multiple return values, as that is a rather common thing to do in Lua. -- last.lua function f (x, y) . Return In Lua, it is possible to return multiple values by following the return keyword with the comma separated return values. I know that a pcall returns two values, that's why you do stuff like: local success, errormessage = pcall(function() But what are these values? Create a custom function with variables for wins, losses, and ties. Return In Lua, it is possible to return multiple values by following the return keyword with the comma separated return values. Quoting from Programming in Lua 5.1 - Multiple Results. Lua does multiple returns like python per the docs for lua. On Wed, Jul 4, 2012 at 3:30 PM, Dvir Volk < dvi. The protect factory receives a function that might raise exceptions and returns a function that respects our return value convention. Use a comma to separate them. It will return the status and anything returned by the function. We must start by creating a C function that registers our Lua2C table. to kickas.@googlegroups.com. Both Lua and Go generalize this to statements like this, which swaps two values: x,y = y,x. Execute the Lua chunk using one of the call functions such as lua_pcall() . example_5_access_lua_function.hpp: 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: Run the loaded Lua script : Retrieve the return from the Lua script: Various pops and stack calls: Close the . I have been using this VM/compiler as the primary script host in Rubble (a scripted templating system used to generate data files for the game Dwarf Fortress) for over a year . 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: An in-game example would be returning how many wins, losses, and ties, a player has. Type return followed by each variable. 4.1. Lua always adjusts the number of results from a function to the circumstances of the call. It creates a Lua state, opens the embedded module, creates a counter object, and returns a wrapped counter object. Lua is a powerful, efficient, lightweight, embeddable scripting language. doesn't return 0) and returns 2, LUA_ERRRUN I then use lua_tostring(L, -1) to find the reason for . If everything's peachy, it will return LUA_OK, which happens to be defined as 0. Let's say that you want to set a variable to a constant and then use that constant multiple times in a calculation. - the test case right now is to register one function with lua, which outputs all of the variables passed . Passing Tables to Lua Functions A use case that happens often is the passing of tables to and from Lua functions. I've tried it multiple times and results are about the same. The other return variable is a status to tell you whether or not the function worked. Return values expected ( Lua function support multiple results reture) Let say my lua function name call f in last.lua, takes 2 parameters. Extract the return values, using the functions: int lua_tointeger(lua_state *L, int stackLocation) Grab an integer value off the lua stack. passed around as arguments, etc. example_5_access_lua_function.hpp: (full source code of example) Illustration - during a private Lua course at a customer's office. 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 argument separatly to the Lua stack. Check return values: (If there was an error) set sqlstate to error, for example '45000', and return false. All API functions and related types and constants are declared in the header file lua.h. Meaning that each counter object will be independent from one another. For example: function triple (x) return x, x, x end. When calling a function, to save these values, you must use the following syntax: local a, b, c = triple (5) Which will result in a = b = c = 5 in this case. return value of the function or error message if an error occurred inside the function block. These are the top rated real world C++ (Cpp) examples of lua_pcall extracted from open source projects. But however, this is a quick way to do it. Type return followed by each variable. Functions in Lua can return multiple results. Either email addresses are anonymous for this group or you need the view member email addresses permission to view the original message. [WoW][3.0.9] A way to get return values from Lua Functions; If this is your first visit, be sure to check out the FAQ. Use of pcall() The most popular use of pcall() . 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. Calling any Lua function from C is similar to this code: Grab the function using lua_getglobal(), push arguments, make a lua_pcall(), and then process the results. Beneath the variable, type return and the name of the variable. local function getWinRate() local wins = 4. local losses = 0. Almost all ads disappear when you login. It is just a Lua program that will run in the Redis engine's context. Here is a (quick, 5-sample, multiple-iterations) benchmark of the same thing using lua_call rather than lua_pcall: Bam, now its all even! (written 2009-08-13, updated 2010-06-19) How is that handled? Go and Lua don't have a try-catch statement , but the pcall function in Lua is analogous, and similarly the panic/recover construct in Go. > EVAL "return 'Hello, scripting!'" 0 "Hello, scripting!" In this example, EVAL takes two arguments. Type conversion from Redis protocol replies (i.e., the replies from redis.call() and redis.pcall() to Lua data types depends on the Redis Serialization Protocol version used by the . Test the code to see the returned string in the output window. . function maximum (a) local mi = 1 -- maximum index local m = a [mi] -- maximum value for i,val in ipairs (a) do if val > m then mi = i m = val end end return m, mi end print (maximum ( {8,10,23,12,5})) --> 23 3 Lua always adjusts the number of results from a function to the circumstances of the call. I make lua_pcall by telling Lua I have 2 params and expect 1 value return. (4) stack manipulation (clear the stack) Let's go straight for the test phase. The first return value is at index -1, the second return . glue.shift(t,i,n) -> t. Shift all the array elements starting at index i, n positions to the left or further to the right.. For a positive n, shift the elements further to the right, effectively creating room for n new elements at index i.When n is 1, the effect is the same as for table.insert(t, i, t[i]).The old values at index i to i+n-1 are preserved, so #t still works after the shifting. The return value is a boolean true in case the current user has permissions to execute the . C++ (Cpp) lua_pcall - 30 examples found. Upon success, I retrieve the return value from the top of the stack. local function sayHi() local printThis = "Hi". If you need to use multiple Lua objects that . C++ (Cpp) lua_pcall - 30 examples found. There is no try/except statement in Lua, but there is a function pcall (or 'protected call') which will call a Lua function safely. Creating the Lua2C table and binding the 'open' function to the Lua2C table. (If the result set is empty) set sqlstate to not found, for example '02000', and return nil. So remember, this lua_pcall() is lua_pcall(L, 1, 1, 0). There should be no issue with exports or function reference calls supporting multiple return values. Show original message. Both for sending arguments and obtaining return values, Lua silently corrects the number of values to match the numbers passed to lua_pcall(); if not enough values are provided, the remainder are filled in with nil values, and if there are extras, they are silently discarded. See . Sometimes you may want multiple values returned from a function. (3) reading out Lua values from Lua stack. (using pcall and xpcall), . Lua exports only allowing a single return value. 4 Likes. Standard library - Go is larger . Now we can rewrite the top-level task function in a much cleaner way: task = protect ( function (arg1, arg2, .)
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