https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69349
Bug ID: 69349
Summary: template substitution error for flexible array members
Product: gcc
Version: 6.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: msebor at gcc dot gnu.org
Target Milestone: ---
While working on a fix for bug 69251 I noticed the following problem.
The following valid test case fails with both 5.3 and 6.0. It is accepted by
Clang.
$ cat x.c && /build/gcc-trunk/gcc/xgcc -B /build/gcc-trunk/gcc -S -Wall -Wextra
-Wpedantic -o/dev/null -xc++ x.c
template <class>
struct A;
template <class T>
struct A<T[]> { typedef int X; };
template <class T> int foo (T&, typename A<T>::X = 0) { return 0; }
struct B { int n, a[]; };
void bar (B *b)
{
foo (b->a);
}
x.c: In function ‘void bar(B*)’:
x.c:13:14: error: no matching function for call to ‘foo(int [])’
foo (b->a);
^
x.c:7:24: note: candidate: template<class T> int foo(T&, typename A<T>::X)
template <class T> int foo (T&, typename A<T>::X = 0) { return 0; }
^~~
x.c:7:24: note: template argument deduction/substitution failed:
x.c: In substitution of ‘template<class T> int foo(T&, typename A<T>::X) [with
T = int []]’:
x.c:13:14: required from here
x.c:7:24: error: invalid use of incomplete type ‘struct A<int []>’
x.c:2:8: note: declaration of ‘struct A<int []>’
struct A;
^
G++ 5.3.0 gives a slightly different error because it treats flexible array
members and zero-length arrays identically:
x.c:9:21: warning: ISO C++ forbids zero-size array ‘a’ [-Wpedantic]
struct B { int n, a[]; };
^
x.c: In function ‘void bar(B*)’:
x.c:13:14: error: no matching function for call to ‘foo(int [0])’
foo (b->a);
^
x.c:7:24: note: candidate: template<class T> int foo(T&, typename A<T>::X)
template <class T> int foo (T&, typename A<T>::X = 0) { return 0; }
^
x.c:7:24: note: template argument deduction/substitution failed:
x.c: In substitution of ‘template<class T> int foo(T&, typename A<T>::X) [with
T = int [0]]’:
x.c:13:14: required from here
x.c:7:24: error: invalid use of incomplete type ‘struct A<int [0]>’
x.c:2:8: note: declaration of ‘struct A<int [0]>’
struct A;
^
