https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110917
Bug ID: 110917
Summary: std::format_to(int*, ...) fails to compile because of
_S_make_span
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Keywords: rejects-valid
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: arthur.j.odwyer at gmail dot com
Target Milestone: ---
// https://godbolt.org/z/9onGvqfha
#include <format>
#include <list>
#include <vector>
void f(std::list<int>::iterator it) {
std::format_to(it, ""); // OK
}
void g(std::vector<int>::iterator it) {
std::format_to(it, ""); // boom!
}
libc++ and Microsoft are both completely happy with this code. libstdc++ is
happy with `f` but unhappy with `g`. I suspect that someplace is accepting
"contiguous iterators of any old T" when it means to limit itself to
"contiguous iterators of char" specifically.
In file included from <source>:1:
.../include/c++/14.0.0/format:2609:36: error: cannot initialize a parameter of
type 'char *' with an rvalue of type 'int *'
2609 | : _Sink<_CharT>(_S_make_span(std::to_address(__out), __n,
_M_buf)),
| ^~~~~~~~~~~~~~~~~~~~~~
.../include/c++/14.0.0/format:3641:32: note: in instantiation of member
function 'std::__format::_Iter_sink<char, __gnu_cxx::__normal_iterator<int *,
std::vector<int>>>::_Iter_sink' requested here
3641 | _Iter_sink<_CharT, _Out> __sink(std::move(__out));
| ^
.../include/c++/14.0.0/format:3683:24: note: in instantiation of function
template specialization
'std::__format::__do_vformat_to<__gnu_cxx::__normal_iterator<int *,
std::vector<int>>, char,
std::basic_format_context<std::__format::_Sink_iter<char>, char>>' requested
here
3683 | { return __format::__do_vformat_to(std::move(__out), __fmt,
__args); }
| ^
.../include/c++/14.0.0/format:3778:19: note: in instantiation of function
template specialization 'std::vformat_to<__gnu_cxx::__normal_iterator<int *,
std::vector<int>>>' requested here
3778 | return std::vformat_to(std::move(__out), __fmt.get(),
| ^
<source>:9:10: note: in instantiation of function template specialization
'std::format_to<__gnu_cxx::__normal_iterator<int *, std::vector<int>>>'
requested here
9 | std::format_to(it, "");
| ^
.../include/c++/14.0.0/format:2574:28: note: passing argument to parameter
'__ptr' here
2574 | _S_make_span(_CharT* __ptr, iter_difference_t<_OutIter> __n,
| ^
1 error generated.
