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nts a function normally declares a variable of type va_list ap in the example that will be manipulated by the macros va_start takes two arguments a va_list object and a reference to the function s last parameter the one before the ellipsis the macro uses this to get its bearings in c23 the second argument will no longer be required and variadic functions will no longer need a named parameter before the ellipsis note 1 5 it initialises the va_list object for use by va_arg or va_copy the compiler will normally issue a warning if the reference is incorrect e g a reference to a different parameter than the last one or a reference to a wholly different object but will not prevent compilation from completing normally va_arg takes two arguments a va_list object previously initialised and a type descriptor it expands to the next variable argument and has the specified type successive invocations of va_arg allow processing each of the variable arguments in turn unspecified behavior occurs if the type is incorrect or there is no next variable argument va_end takes one argument a va_list object it serves to clean up if one wanted to for instance scan the variable arguments more than once the programmer would re initialise your va_list object by invoking va_end and then va_start again on it va_copy takes two arguments both of them va_list objects it clones the second which must have been initialised into the first going back to the scan the variable arguments more than once example this could be achieved by invoking va_start on a first va_list then using va_copy to clone it into a second va_list after scanning the variable arguments a first time with va_arg and the first va_list disposing of it with va_end the programmer could scan the variable arguments a second time with va_arg and the second va_list va_end needs to also be called on the cloned va_list before the containing function returns c edit c describes variadic functions using the params keyword a type must be provided for the arguments although object can be used as a catch all at the calling site you can either list the arguments one by one or hand over a pre existing array having the required element type using the variadic form is syntactic sugar for the latter namespace wikipedia examples using system public class program static int foo int a int b params int args return the sum of the integers in args ignoring a and b int sum 0 foreach int i in args sum i return sum static void main string args console writeline foo 1 2 0 console writeline foo 1 2 3 10 20 33 int manyvalues 13 14 15 console writeline foo 1 2 manyvalues 42 c edit the basic variadic facility in c is largely identical to that in c prior to c 26 the comma before the ellipsis could be omitted c also allows variadic functions without named parameters for example void f however until c 26 there was no portable way to access those arguments because va_start required the name of the last fixed parameter of the function since c 26 c adopts the one argument form of va_start matching c23 and allowing access to the arguments even when the function has no fixed parameters variadic templates parameter pack can also be used in c with language built in fold expressions variadic templates are the only type safe way to have variadic functions parameters in c as c lacks java style non template variadic parameters import std template typename ts void fooprint ts args std print args int main int argc char argv fooprint 1 3 14f 1 3 14 fooprint foo b true nullptr foo b true nullptr the cert coding standards for c strongly prefers the use of variadic templates parameter pack in c over the c style variadic function due to a lower risk of misuse 6 variadic templates are the only way to achieve java style type safe variadic parameters to constrain the parameter to be only of type t similar to t args in java one can use the concept std same_as t u 7 or std convertible_to from to for types which may be intended to be convertible 8 using std same_as equivalent to java declaration t void fn t args template typename t void fn same_as t auto args carbon edit carbon a language designed with interoperability with c in mind offers variadics in particular pack expansions 9 takes an arbitrary number of vectors with arbitrary element types and returns a vector of tuples where the i th element of the vector is a tuple of the i th elements of the input vectors fn zip each elementtype type each vector vector each elementtype vector each elementtype var each iter auto each vector begin var result vector each elementtype while and each iter each vector end result push_back each iter each iter return result fortran edit since the fortran 90 revision fortran functions or subroutines can accept optional arguments 10 the argument list is still fixed but the ones that have the optional attribute can be omitted in the function subroutine call the intrinsic function present can be used to detect the presence of an optional argument the optional arguments can appear anywhere in the argument list program test implicit none real x all arguments are passed call foo 1 2 3 0 4 x outputs 1 2 3 0 4 6 0 the denotes a newline the last 2 arguments are omitted call foo 1 2 3 0 outputs 1 2 3 0 the 2nd and 4th arguments are omitted the arguments that are positioned after an omitted argument must be passed with a keyword call foo 1 c 3 0 e x outputs 1 3 0 6 0 alternatively the fortran 2023 revision has introduced the nil pseudo constant to denote an omitted argument call foo 1 nil 3 0 nil x outputs 1 3 0 6 0 contains the subroutine foo has 2 mandatory and 3 optional arguments subroutine foo a b c d e integer intent in a integer intent in optional b real intent in c integer intent in optional d real intent out optional e print a if present b print b print c if present d print d if present e then e 2 c print c end if end subroutine end program go edit variadic functions in go can be called with any number of trailing arguments 11 fmt println is a common variadic function it uses an empty interface as a catch all type package main import fmt this variadic function takes an arbitrary number of ints as arguments func sum nums int fmt print the sum of nums also a variadic function total 0 for _ num range nums total num fmt println is total also a variadic function func main variadic functions can be called in the usual way with individual arguments sum 1 2 the sum of 1 2 is 3 sum 1 2 3 the sum of 1 2 3 is 6 if you already have multiple args in a slice apply them to a variadic function using func slice like this nums int 1 2 3 4 sum nums the sum of 1 2 3 4 is 10 output the sum of 1 2 is 3 the sum of 1 2 3 is 6 the sum of 1 2 3 4 is 10 java edit as with c the object type in java is available as a catch all in java a parameter can be variadic using the ellipsis notation this is essentially equivalent to an array however it does not require wrapping as an array for example string args and string args would be essentially identical package org wikipedia examples public class program variadic methods store any additional arguments they receive in an array consequentially printargs is actually a method with one parameter a variable length array of string s private static void printargs string strings for string s strings system out println s public static void main string args printargs hello short for printargs new string hello printargs hello world short for printargs new string hello world printargs args prints the entire args array javascript edit javascript does not care about types of variadic arguments the variadic argument is denoted with which denotes a rest parameter which collects the arguments into an array function sum numbers return numbers reduce a b a b 0 console log sum 1 2 3 6 console log sum 3 2 5 console log sum 0 it is also possible to create a variadic function using the arguments object although it is only usable with functions created with the function keyword function sum return array prototype reduce call arguments a b a b 0 console log sum 1 2 3 6 console log sum 3 2 5 console log sum 0 note that in typescript because the rest parameter is an array this is denoted as so function sum numbers number number return numbers reduce a b a b 0 typescript also allows forcing the rest parameter to have an exact number of elements i e a tuple forces exactly three numbers function sumexactlythree numbers number number number number return numbers reduce a b a b 0 forces at least two numbers function sumatleasttwo numbers number number number number return numbers reduce a b a b 0 forces the first argument to be a string then anything after function log args string any lua edit lua functions may pass varargs to other functions the same way as other values using the return keyword tables can be passed into variadic functions by using in lua version 5 2 or higher 12 table unpack or lua 5 1 or lower 13 unpack varargs can be used as a table by constructing a table with the vararg as a value function sum designates varargs local sum 0 for _ v in pairs do creating a table with a varargs is the same as creating one with standard values sum sum v end return sum end values 1 2 3 4 sum 5 table unpack values returns 15 table unpack should go after any other arguments otherwise not all values will be passed into the function function add5 return 5 this is incorrect usage of varargs and will only return the first value provided end entries function process_entries local processed for i v in pairs entries do processed i v placeholder processing code end return table unpack processed returns all entries in a way that can be used as a vararg end print process_entries the print function takes all varargs and writes them to stdout separated by newlines pascal edit pascal is standardized by iso standards 7185 standard pascal and 10206 extended pascal neither standardized form of pascal supports variadic routines except for certain built in routines read readln and write writeln and additionally in ep readstr writestr nonetheless dialects of pascal implement mechanisms resembling variadic routines delphi defines an array of const data type that may be associated with the last formal parameter within the routine definition the array of const is an array of tvarrec an array of variant records 14 the vtype member of the aforementioned record data type allows inspection of the argument s data type and subsequent appropriate handling the free pascal compiler supports delphi s variadic routines too 15 this implementation however technically requires a single argument that is an array pascal imposes the restriction that arrays need to be homogenous this requirement is circumvented by utilizing a variant record the gnu pascal defines a real variadic formal parameter specification using an ellipsis but as of 2022 no portable mechanism to use such has been defined 16 both gnu pascal and freepascal allow externally declared functions to use a variadic formal parameter specification using an ellipsis php edit php does not care about types of variadic arguments unless the argument is typed function sum nums int return array_sum nums echo sum 1 2 3 6 and typed variadic arguments function sum int nums int return array_sum nums echo sum 1 a 3 typeerror argument 2 passed to sum must be of the type int since php 7 3 python edit python does not care about types of variadic arguments from typing import any def foo a any b any args tuple any none print args args is a tuple immutable sequence if __name__ __main__ foo 1 2 args foo 1 2 3 args 3 foo 1 2 3 hello args 3 hello keyword arguments can be stored in a dictionary from typing import any unpack def bar args tuple any kwargs unpack dict str any any function body note that even though args has type tuple any args is sometimes annotated with typing any 17 raku edit in raku the type of parameters that create variadic functions are known as slurpy array parameters and they re classified into three groups flattened slurpy edit these parameters are declared with a single asterisk and they flatten arguments by dissolving one or more layers of elements that can be iterated over i e iterables sub foo a b args say args perl foo 1 2 foo 1 2 3 3 foo 1 2 3 hello 3 hello foo 1 2 3 4 5 6 3 4 5 6 unflattened slurpy edit these parameters are declared with two asterisks and they do not flatten any iterable arguments within the list but keep the arguments more or less as is sub bar a b args say args perl bar 1 2 bar 1 2 3 3 bar 1 2 3 hello 3 hello bar 1 2 3 4 5 6 3 4 5 6 contextual slurpy edit these parameters are declared with a plus sign and they apply the single argument rule which decides how to handle the slurpy argument based upon context simply put if only a single argument is passed and that argument is iterable that argument is used to fill the slurpy parameter array in any other case works like i e unflattened slurpy sub zaz a b args say args perl zaz 1 2 zaz 1 2 3 3 zaz 1 2 3 hello 3 hello zaz 1 2 4 5 4 5 single argument fills up array zaz 1 2 3 4 5 3 4 5 behaving as zaz 1 2 3 4 5 6 3 4 5 6 behaving as ruby edit ruby does not care about types of variadic arguments def foo args print args end foo 1 prints 1 nil foo 1 2 prints 1 2 nil rust edit rust does not support variadic arguments in functions instead it uses macros which support variadic arguments 18 this is essentially why println is a macro and not a function as it takes variadic arguments to format macro_rules calculate the pattern for a single eval eval e expr let val usize e force types to be integers println stringify e val decompose multiple eval s recursively eval e expr eval es expr calculate eval e calculate eval es fn main calculate eval 1 2 eval 3 4 eval 2 3 1 rust is able to interact with c s variadic system via a c_variadic feature switch as with other c interfaces the system is considered unsafe to rust and marked with c linkage 19 the variadic parameter itself is annotated with and the function may be marked safe if it is guaranteed not to access its variadic arguments 20 feature c_variadic pub unsafe extern c fn add n usize mut args usize let mut sum 0 for _ in 0 n sum args arg usize sum scala edit object program variadic methods store any additional arguments they receive in an array consequentially printargs is actually a method with one parameter a variable length array of string s private def printargs strings string unit strings foreach println def main args array string unit printargs hello short for printargs hello printargs hello world short for printargs hello world swift edit swift cares about the type of variadic arguments but the catch all any type is available func greet timeoftheday string names string here names is string print looks like we have names count people for name in names print hello name good timeoftheday greet timeoftheday morning names joseph clara william maria output looks like we have 4 people hello joseph good morning hello clara good morning hello wil...