------- Comment #20 from matz at gcc dot gnu dot org 2010-08-11 16:10 -------
A conforming variant of what you probably are trying to code is:
--------------------------------------------------------------------
#include <stdio.h>
#include <stdarg.h>
void format_indirect(char* dst_buffer, size_t dst_buffer_size_bytes,
const char *format, va_list va)
{
vsnprintf(dst_buffer, dst_buffer_size_bytes, format, va);
dst_buffer[dst_buffer_size_bytes-1]=0;
}
void format_direct(char* dst_buffer, size_t dst_buffer_size_bytes,
const char* format, ...)
{
va_list va;
va_start (va, format);
format_indirect(dst_buffer, dst_buffer_size_bytes, format, va);
va_end (va);
}
int main(void)
{
char buffer[1000];
format_direct((char*)buffer, sizeof(buffer), "%s %s", __DATE__, __TIME__);
printf("Result: \"%s\"\n", buffer);
return 0;
}
-----------------------------------------------------------
Note how the va_list is constructed in the function that actually is
a varargs one, in particular how the necessary parameter is mentioned.
Note further how that va_list is passsed to the function that is not
varargs in order to capture all variable arguments of its caller.
There, no assumption on stack-layout. It will work with all types and
ABIs, even those that happen to pass even some varargs in registers,
not on the stack.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45249
