http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50581
--- Comment #1 from joseph at codesourcery dot com <joseph at codesourcery dot com> 2011-09-30 19:41:17 UTC --- There is no possible valid use of passing arrays to va_arg. In C99, it is never possible for an array to be passed by value to a function because it will have decayed to a pointer before the call. Thus, any execution of va_arg with such an argument type results in undefined behavior, just like calling it with "char" or "float", and generating a runtime abort (with a compile-time warning) might be appropriate, as is done for "char" and "float". In C90, it is technically possible to use va_arg in this case without undefined behavior. The argument passed to the function would have to be a non-lvalue array - for example, an array in a structure returned from another function. The result of va_arg would itself be a non-lvalue array, which it is not possible to convert to a pointer, so it is not possible to access the values in the array in any way; all that can be done is to discard the value (call va_arg for its side effects) or to pass it to another variadic function. As far as I know this obscure C90-only use case works correctly (so you can access arguments after the non-lvalue array using va_arg again, for example). If you have problems with it, please provide a bug report with a valid C90 testcase. E.g., #include <stdarg.h> typedef char array[1]; struct s { array a; }; struct s f (void); void g (int a, ...); void h (void) { g (0, f().a); } void g (int a, ...) { va_list ap; va_start (ap, a); va_arg (ap, array); va_end (ap); }