https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105918
Bug ID: 105918 Summary: Spurious Warray-bounds in std::to_chars Product: gcc Version: 12.1.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ Assignee: unassigned at gcc dot gnu.org Reporter: ed at catmur dot uk Target Milestone: --- #include <charconv> template<int N> std::to_chars_result toChars(char (& buf)[N], int number) { char temp[N]; std::to_chars_result result = std::to_chars(temp, temp + N, number); if (result.ec != std::errc()) return result; char* it = temp; char* end = result.ptr; std::size_t i = 0u; while (i != N && it != end) buf[i++] = *it++; if (i != N) buf[i] = '\0'; return std::to_chars_result{.ptr = buf + (result.ptr - temp), .ec = std::errc()}; } #include <memory> struct ar { struct V { bool value; } value; std::unique_ptr<int> s; }; void f(...); ar g(); ar evaluate(bool value) { ar res{value}; if (res.value.value) return res; return g(); } #define CHECK(P) f(0, 0, 0, 0, 0, 0, 0, 0, 0, 0, evaluate(P), 0, 0, 0, 0, 0, 0, 0, 0, 0 ); int main() { char s3[3]; auto res3 = toChars(s3, 12); CHECK((res3.ec == std::errc())); CHECK((s3[0] == '1')); CHECK((s3[1] == '2')); CHECK((s3[2] == '\0')); char s1[1]; auto res1 = toChars(s1, 12); CHECK((res1.ec != std::errc())); } Compiled at -O3 -Warray-bounds: In file included from include/c++/12.1.0/charconv:42, from <source>:1: In function 'void std::__detail::__to_chars_10_impl(char*, unsigned int, _Tp) [with _Tp = unsigned int]', inlined from 'std::__detail::__integer_to_chars_result_type<_Tp> std::__detail::__to_chars_10(char*, char*, _Tp) [with _Tp = unsigned int]' at include/c++/12.1.0/charconv:225:35, inlined from 'std::__detail::__integer_to_chars_result_type<_Tp> std::__to_chars_i(char*, char*, _Tp, int) [with _Tp = int]' at include/c++/12.1.0/charconv:351:32, inlined from 'std::to_chars_result std::to_chars(char*, char*, int, int)' at include/c++/12.1.0/charconv:370:1, inlined from 'std::to_chars_result toChars(char (&)[N], int) [with int N = 1]' at <source>:7:48: include/c++/12.1.0/bits/charconv.h:95:22: warning: array subscript 1 is outside array bounds of 'char [1]' [-Warray-bounds] 95 | __first[1] = __digits[__num + 1]; | ~~~~~~~~~~~^~~~~~~~~~~ <source>: In function 'std::to_chars_result toChars(char (&)[N], int) [with int N = 1]': <source>:6:10: note: at offset 1 into object 'temp' of size 1 6 | char temp[N]; | ^~~~ <source>:6:10: note: at offset 2 into object 'temp' of size 1 Compiler returned: 0