vasprintf
extern int vasprintf(char **ret, char const *format, va_list ap);
extern int vasprintf(char **ret, char const *format, va_list ap);
vasprintf(&p, fmt, ap);
if ((len = vasprintf(&buf, format, args)) == -1) {
#define nv_vasprintf(ptr, ...) vasprintf(ptr, M_NVLIST, __VA_ARGS__)
#define nv_vasprintf(ptr, ...) vasprintf(ptr, __VA_ARGS__)
extern int vasprintf (char **__restrict __ptr, const char *__restrict __f,
weak_alias (_IO_vasprintf, vasprintf)
done = vasprintf (string_ptr, format, arg);