Variadic function: Difference between revisions

Revision as of 17:16, 9 March 2024

Revision as of 15:47, 27 July 2024

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# {{code|va_copy}} takes two arguments, both of them {{code|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 {{code|va_start}} on a first {{code|va_list}}, then using {{code|va_copy}} to clone it into a second {{code|va_list}}. After scanning the variable arguments a first time with {{code|va_arg}} and the first {{code|va_list}} (disposing of it with {{code|va_end}}), the programmer could scan the variable arguments a second time with {{code|va_arg}} and the second {{code|va_list}}. {{code|va_end}} needs to also be called on the cloned {{code|va_list}} before the containing function returns.

''I

===In C#===

[[C Sharp (programming language)|C#]] describes variadic functions using the {{code|params}} keyword. A type must be provided for the arguments, although {{code|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.

<syntaxhighlight lang="c#" highlight="5,16-17,19">

using System;

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 = new int[] { 13, 14, 15 };

Console.WriteLine(Foo(1, 2, manyValues)); // 42

}

}

</syntaxhighlight>

===In C++===