opt.c

#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdarg.h>

int p_open(const char *path, int flags, ...)
{
	mode_t mode = 0;

	if (flags & O_CREAT) {
		va_list arg_list;

		va_start(arg_list, flags);
		mode = (mode_t)va_arg(arg_list, int);
		va_end(arg_list);
	}

	return mode;
}

int main(int argc, char **argv)
{
	int mode;

	mode = p_open("foo", O_CREAT, 0666);

	printf("mode %4o\n", mode);
	return 0;
}