4.1. When we call a function as a statement, Lua discards all results from the function. Test the code to see the returned string in the output window. You can rate examples to help us improve the quality of examples. The Auxiliary Library. Upon success, I retrieve the return value from the top of the stack. example_5_access_lua_function.hpp: Quoting from Programming in Lua 5.1 - Multiple Results. /* 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. return a String to Print Expected Output Expand. local f, err = io.open(filename) if err ~= nil then return "",err end. . This is intended to allow easy embedding into Go programs, with minimal fuss and bother. I believe you meant you can return any value of any datatype. It supports procedural programming, object-oriented programming, functional programming, data-driven programming, and data description. local function sayHi() local printThis = "Hi". end ) The Lua . You might also consider to support multiple return values, as that is a rather common thing to do in Lua. The caller can expect any number of values returned: . > EVAL "return 'Hello, scripting!'" 0 "Hello, scripting!" In this example, EVAL takes two arguments. (full source code of example) Illustration - during a private Lua course at a customer's office. C++ (Cpp) lua_pcall - 30 examples found. I've tried it multiple times and results are about the same. 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. Let's say that you want to set a variable to a constant and then use that constant multiple times in a calculation. An in-game example would be returning how many wins, losses, and ties, a player has. 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? 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 } passed around as arguments, etc. It is also possible to ignore returned values by using the throwaway variable _ in the . 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. -- last.lua function f (x, y) . The script doesn't need to include any definitions of Lua function. Either email addresses are anonymous for this group or you need the view member email addresses permission to view the original message. You can rate examples to help us improve the quality of examples. forget about having multiple Lua states, about binding CompCompiler in those states, about the LuaInstance singleton, zipped code, and so on. 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. Lua can return multiple values so both the "fast" and "slow" functions return its own counter and the counter for the other 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: It seems that as of Lua 5.2 the return value isn't specified for tables where the set of integer indices has "holes . (If there was a result set) Copy the result set to sqlresult. One way to do this in Lua is to set a global variable and then refer to that . [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. 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! The other return variable is a status to tell you whether or not the function worked. 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. These are the top rated real world C++ (Cpp) examples of lua_pcall extracted from open source projects. 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; . (2) getting Lua values on Lua stack. Return In Lua, it is possible to return multiple values by following the return keyword with the comma separated return values. 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: The flag that allows a script to access keys from multiple slots. Lua does multiple returns like python per the docs for lua. Well, it is a pretty simple way of getting return values, and there certainly are better ways. The files under /usr/share/luajit-2../jit are part of LuaJIT's jit library, which provides a Lua API to the JIT compiler. Return values expected ( Lua function support multiple results reture) Let say my lua function name call f in last.lua, takes 2 parameters. Execute the Lua chunk using one of the call functions such as lua_pcall() . 3 Answers. Granted, Wc3 natives never have multiple return values, but this would extend the scope of application to user-written functions. Lua combines simple procedural syntax with powerful data description constructs based on associative arrays and extensible semantics. Create a custom function with variables for wins, losses, and ties. We must start by creating a C function that registers our Lua2C table. 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++. This data structure is a kind of unique session variable allowing multiple Lua scripting engine . It is just a Lua program that will run in the Redis engine's context. . The protect factory receives a function that might raise exceptions and returns a function that respects our return value convention. When we use a call as an expression, Lua keeps only the first result. If you need to use multiple Lua objects that . See . (written 2009-08-13, updated 2010-06-19) 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. It's not a good idea to only skim through the comments before you press the submit button. @gmail.com > wrote: . 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. Lua always adjusts the number of results from a function to the circumstances of the call. doesn't return 0) and returns 2, LUA_ERRRUN I then use lua_tostring(L, -1) to find the reason for . How is that handled? But however, this is a quick way to do it. to kickas.@googlegroups.com. Lua exports only allowing a single return value. Return In Lua, it is possible to return multiple values by following the return keyword with the comma separated return values. An in-game example would be returning how many wins, losses, and ties, a player has. These are the top rated real world C++ (Cpp) examples of lua_pcall extracted from open source projects. Type return followed by each variable. They would just be treated as arrays in the C# and JS script runtimes. So remember, this lua_pcall() is lua_pcall(L, 1, 1, 0). It will return the status and anything returned by the function. The Application Program Interface . return value of the function or error message if an error occurred inside the function block. 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. 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. Standard library - Go is larger . 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. It creates a Lua state, opens the embedded module, creates a counter object, and returns a wrapped counter object. local function getWinRate() local wins = 4. local losses = 0. The first argument is a string that consists of the script's Lua source code. lua_pop(L, 1); /* pop returned value */ debugging2 = stackDump(instEnum);} . Creating the Lua2C table and binding the 'open' function to the Lua2C table. I make lua_pcall by telling Lua I have 2 params and expect 1 value return. 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. An attempted fix was initially PRd in: fix (scripting/lua): support exported MRVs . Passing Tables to Lua Functions A use case that happens often is the passing of tables to and from Lua functions. gottfriedleibniz June 9, 2021, 9:04pm #2. Following is the source code for a function called max(). local ret1 = assert (task1 (arg1)) local ret2 = assert (task2 (arg2)) . Example. (4) stack manipulation (clear the stack) Let's go straight for the test phase. Example. 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. Type return followed by each variable. Functions in Lua can return multiple results. Use a comma to separate them. Almost all ads disappear when you login. C++ (Cpp) lua_pcall - 30 examples found. 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. (If the result set is empty) set sqlstate to not found, for example '02000', and return nil. 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: 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 . (3) reading out Lua values from Lua stack. 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. Sorted by: 29. you could do something like this if you aren't sure how many values some function may return. There is no try/except statement in Lua, but there is a function pcall (or 'protected call') which will call a Lua function safely. Extract the return values, using the functions: int lua_tointeger(lua_state *L, int stackLocation) Grab an integer value off the lua stack. 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. On Wed, Jul 4, 2012 at 3:30 PM, Dvir Volk < dvi. Below the function, use print () to call the new function. 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: example_5_access_lua_function.hpp: Create a custom function with variables for wins, losses, and ties. Both Lua and Go generalize this to statements like this, which swaps two values: x,y = y,x. You have to register before you can post. Now we can rewrite the top-level task function in a much cleaner way: task = protect ( function (arg1, arg2, .) Multiple return values - supported by both languages Strings are immutable in both languages C/C++ interfacing - Well developed in Lua . (using pcall and xpcall), . Show original message. . As well as private training courses on site, we run public Lua courses at our Melksham, Wiltshire, UK training centre. This section describes the C API for Lua, that is, the set of C functions available to the host program to communicate with Lua. 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. This function takes two parameters num1 and num2 and returns the maximum between the two Beneath the variable, type return and the name of the variable. 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. Following is the source code for a function called max(). Sometimes you may want multiple values returned from a function. Both function calls and vararg expressions can result in multiple values. Again, notice that the stack enables the transfer.
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