https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97253
Bug ID: 97253
Summary: [c++20] last character not shown when printing out
std::array <char> via -Wunused-local-typedefs
Product: gcc
Version: 11.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: dimitri.gorokhovik at free dot fr
Target Milestone: ---
The following code:
#include <array>
#include <cstdio>
template <auto M> struct s { constexpr static auto m = M; };
int main ()
{
constexpr auto s1 = s <std::array <char, 4> { 'a', 'b', 'c', 'd' }> {};
constexpr auto s2 = s <std::array <wchar_t, 4> { 'a', 'b', 'c', 'd' }> {};
using _1 = decltype (s1);
using _2 = decltype (s2);
for (auto i : s1.m)
printf ("%c", i);
printf ("\n");
return 0;
};
when built as:
g++ -std=c++20 -Wunused-local-typedefs -o bug-7 bug-7.cpp && ./bug-7
produces the following warnings:
bug-7.cpp: In function ‘int main()’:
bug-7.cpp:11:9: warning: typedef ‘using _1 = const struct s<std::array<char,
4>{"abc"}>’ locally defined but not used [-Wunused-local-typedefs]
11 | using _1 = decltype (s1);
| ^~
bug-7.cpp:12:9: warning: typedef ‘using _2 = const struct s<std::array<wchar_t,
4>{std::__array_traits<wchar_t, 4>::_Type{97, 98, 99, 100}}>’ locally defined
but not used [-Wunused-local-typedefs]
12 | using _2 = decltype (s2);
| ^~
When it is run, the output is:
abcd
I.e., when the warning displays the contents of the literal of the type
std::array <char>, it presents it as a character string ("abc") in which the
last character is missing ('d' in this example). This doesn't happen when the
array type doesn't allow to show it as char string -- all array elements are
shown.
Running the binary confirms that the array literal actually contains the
non-shown character.
g++ (GCC) 11.0.0 20200924 (experimental)
