Can someone explain why this outputs garbage values?

[Dustin via Digitalmars-d-learn]

I'm trying to work with some c functions that make use of varargs 
and I'm trying to push my d varargs to c varargs.


http://dpaste.dzfl.pl/ad08a6197963

Code:
___
import core.vararg;
import std.string : toStringz;
import std.c.stdio;

char[256] buffer;

void print(string format, ...)
{
char* dest = buffer.ptr;
snprintf(dest, 256UL, toStringz(fmt), _argptr);
printf(dest);
}

void main(string[] args)
{
print(%d, %d, %d\n, 1, 2, 3);
}
___
Output: -1080890848, 1073915632, 3

Re: Can someone explain why this outputs garbage values?

[Dustin via Digitalmars-d-learn]

On Tuesday, 9 December 2014 at 20:24:18 UTC, Adam D. Ruppe wrote:
Also, the reason why the special function is needed is that the 
argptr is just a pointer to the arguments. If you pass that to 
printf, how does it know that there's varargs on the other end 
instead of just being another pointer whose numeric value it is 
supposed to print out?


I got it to work with vsnprintf with the following code:
___
import core.vararg;
import std.string : toStringz;
import std.c.stdio : printf;

char[256] buffer;

extern(C) void vsnprintf(char* s, ulong n, const(char*) format, 
va_list arg);


void print(string fmt, ...)
{
char* dest = buffer.ptr;

va_list list;
va_start(list, fmt);
vsnprintf(dest, 256UL, toStringz(fmt), list);
printf(dest);
}

void main(string[] args)
{
print(%d, %d, %d\n, 1, 2, 3);
}
___

I did have to declare my own function prototype because importing 
vsnprintf from std.c.stdio produced the following error: 
test.d(13): Error: function core.stdc.stdio._vsnprintf (char* s, 
ulong n, const(char*) format, __va_list_tag* arg) is not callable 
using argument types (char*, ulong, immutable(char)*, char*)


It works fine with my own function declaration though...
(I'm using LDC on Win64)