https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108269
Bug ID: 108269
Summary: Incorrect __PRETTY_FUNCTION__ with std::array<char> in
C++20 NTTP literal
Product: gcc
Version: 13.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: camden.mannett at gmail dot com
Target Milestone: ---
Created attachment 54176
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=54176&action=edit
Source code
When std::array<char, N> is used within a literal type that is used as an NTTP,
it _looks_ like the __PRETTY_FUNCTION__ output always assumes that it is a
null-terminated string which is then displayed without the last character - but
it is not always a null!
It is simplest to demonstrate with a compile-time string implementation
(https://godbolt.org/z/8EnPfeWq7):
#include <algorithm>
#include <array>
#include <iostream>
namespace {
template<typename T>
class type_string_t
{
[[nodiscard]] constexpr static std::string_view generate() noexcept
{
constexpr auto sig =
std::string_view{ static_cast<const char*>(__PRETTY_FUNCTION__) };
return sig;
}
public:
constexpr static auto value = generate();
};
template<typename T>
constexpr auto type_string = type_string_t<T>::value;
template<std::size_t N>
class str_storage
{
public:
constexpr str_storage(const char (&str)[N])
{
std::copy_n(&str[0], N, value.begin());
}
constexpr str_storage(char c)
: value{ c }
{
}
std::array<char, N> value;
};
str_storage(char) -> str_storage<1>;
template<str_storage S>
struct str
{};
}
int
main()
{
std::cout << type_string<str<'a'>> << "\n"
<< type_string<str<"a">> << "\n"
<< type_string<str<"hello">> << std::endl;
return 0;
}
This yields pretty much what you would expect when built via Clang (after
removal of cruft):
(anonymous namespace)::str<{{{97}}}>
(anonymous namespace)::str<{{"a"}}>
(anonymous namespace)::str<{{"hello"}}>
However gcc does something different when the std::array contains only a single
char:
{anonymous}::str<{anonymous}::str_storage<1>{std::array<char, 1>{""}}>
{anonymous}::str<{anonymous}::str_storage<2>{std::array<char, 2>{"a"}}>
{anonymous}::str<{anonymous}::str_storage<6>{std::array<char, 6>{"hello"}}>
It seems to always represent the char array as a null-terminated string
literal, which isn't always true.
