How do I fill a va_list

c, variadic-functions

Solution

There's no ability to fill a va_list explicitly.

You should write a wrapper function. Say you need to call your function foo, instead of manually filling in a va_list, you define a new function like so:

void call_foo(int arg1, ...)
{
   va_list ap;
   va_start(ap, arg1);
   foo(arg1, ap);
   va_end(ap);
}

Now you can call `foo`, which takes a va_list, however you like, by doing e.g. call_foo(1,2,3,4);, call_foo(1, 1, "Hello"); etc.

This will only allow you to specify the arguments at compile time, you can't build the arguments at runtime.

Problem

If I have a va_list I know how to extract all its elements: ``` void printInts(int n,...) { va_list va; va_start(va, n); for(unsigned int i=0; i<n; i++) { int arg=va_arg(va, int); printf("%d",arg); } va_end(va); } ``` So when I call printInts(3,1,2,3) the va_list get filled of all the parameters. But how do I manually fill a va_list without using va_start? I mean that I want something like: ``` va_list va; push_arg(va, int, 5); // And so on until I fill all parameters ... ``` I need this because there is a function that accept a va_list as argument, and I don't know how to fill that va_list of all its parameters.

Original source