How to create a function to call a variable arg function?

Question

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C/C++: Passing variable number of arguments around

I need to put all functions calling into a C API into a separate source file unit. It is due to defines interfering with other code. So to keep the possibly interfering code separate.

Anyway, most functions are eg int function2(int) so I just implement in separate file like this:

int XXfunction1(int val) { return function(val) }

But I also have functions with variable arguments like this:

extern int function2(int, ...)

So how can I write my own function which calls that?

This doesn't seem to work:

int XXFunction2(int val, ...) {
   return function2(val, ...);
}

How do I write the function?

score 4 · Accepted Answer · edited Aug 12 '11 at 19:26

4

You need a "v" version of your method that can take a variadic list.

int function2v(int val, va_list arg_list)
{
    //Work directly with the va_list
}

//And to call it
int XXFunction2(int val, ...) {
   int returnVal;
   va_list list;
   va_start(list, val);

   returnVal = function2v(val, list);

   va_end(list);

   return returnVal;
}

edited Aug 12 '11 at 19:26

answered Aug 12 '11 at 19:09

Joe

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score -1 · Answer 2 · answered Aug 12 '11 at 19:08

-1

Function2 must be declared before XXFunction2 for it to work. What you can do is to but the function signature on a .h file and import it before using, otherwise C can't find Function2 while compiling XXFunction2, leading to a compiling error.

answered Aug 12 '11 at 19:08

Lucas Famelli

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2

This answer isn't relevant to the question at hand. – Josh Matthews Aug 12 '11 at 19:13
Accurate as far as it goes, but missing the point of the question. – Jonathan Leffler Aug 12 '11 at 19:14

How to create a function to call a variable arg function?

2 Answers2