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incautiously can give rise to a class of security holes known as format string attacks the attack is possible because the language support for variadic functions is not type safe it permits the function to attempt to pop more arguments off the stack than were placed there corrupting the stack and leading to unexpected behavior as a consequence of this the cert coordination center considers variadic functions in c to be a high severity security risk 1 in functional programming languages variadics can be considered complementary to the apply function which takes a function and a list sequence array as arguments and calls the function with the arguments supplied in that list thus passing a variable number of arguments to the function citation needed in the functional language haskell variadic functions can be implemented by returning a value of a type class t if instances of t are a final return value r and a function t t x t this allows for any number of additional arguments x further explanation needed a related subject in term rewriting research is called hedges or hedge variables 2 unlike variadics which are functions with arguments hedges are sequences of arguments themselves they also can have constraints take no more than 4 arguments for example to the point where they are not variable length such as take exactly 4 arguments thus calling them variadics can be misleading however they are referring to the same phenomenon and sometimes the phrasing is mixed resulting in names such as variadic variable synonymous to hedge note the double meaning of the word variable and the difference between arguments and variables in functional programming and term rewriting for example a term function can have three variables one of them a hedge thus allowing the term to take three or more arguments or two or more if the hedge is allowed to be empty examples edit this section may contain excessive or irrelevant examples please help improve it by removing less pertinent examples and elaborating on existing ones october 2025 learn how and when to remove this message c edit to portably implement variadic functions in the c language the standard stdarg h header file is used the older varargs h header has been deprecated in favor of stdarg h in c the header file cstdarg is used 3 include stdarg h include stdio h double average int count va_list ap double sum 0 va_start ap count before c23 requires the last fixed parameter to get the address for int j 0 j count j sum va_arg ap int increments ap to the next argument va_end ap return sum count int main int argc char argv printf f n average 3 1 2 3 return 0 this will compute the average of an arbitrary number of arguments note that the function does not know the number of arguments or their types the above function expects that the types will be int and that the number of arguments is passed in the first argument this is a frequent usage but by no means enforced by the language or compiler in some other cases for example printf the number and types of arguments are figured out from a format string in both cases this depends on the programmer to supply the correct information alternatively a sentinel value like null or nullptr may be used to indicate the end of the parameter list if fewer arguments are passed in than the function believes or the types of arguments are incorrect this could cause it to read into invalid areas of memory and can lead to vulnerabilities like the format string attack depending on the system even using null as a sentinel may encounter such problems nullptr or a dedicated null pointer of the correct target type may be used to avoid them stdarg h declares a type va_list and defines four macros va_start va_arg va_copy and va_end each invocation of va_start and va_copy must be matched by a corresponding invocation of va_end when working with variable arguments 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 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