https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80662
Bug ID: 80662
Summary: libstdc++ basic_string casting oddity
Product: gcc
Version: 7.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: dje at gcc dot gnu.org
Target Milestone: ---
Target: x86-64
// https://twitter.com/zxovq/status/861377261827629057
#include <sstream>
#include <string>
class my_stream : public std::stringstream {
public:
operator std::string() const
{
return std::stringstream::str();
}
template<typename T>
my_stream& operator<<(T&& value)
{
std::stringstream::operator<<(std::forward<T>(value));
return *this;
}
};
int main(void)
{
// for an unknown reason gcc 7.1 implicitly casts (my_stream{} << "")
// to std::basic_ostream& instead of using my_stream&
// gcc 6.3 is fine; uncomment static_cast below to make gcc 7.1 work
std::string s{/*static_cast<my_stream&>*/(my_stream{} << "hello world")};
}
<source>: In function 'int main()':
<source>:24:76: error: no matching function for call to
'std::__cxx11::basic_string<char>::basic_string(<brace-enclosed initializer
list>)'
std::string s{/*static_cast<my_stream&>*/(my_stream{} << "hello world")};
^
In file included from
/opt/compiler-explorer/gcc-7.1.0/include/c++/7.1.0/string:52:0,
from
/opt/compiler-explorer/gcc-7.1.0/include/c++/7.1.0/bits/locale_classes.h:40,
from
/opt/compiler-explorer/gcc-7.1.0/include/c++/7.1.0/bits/ios_base.h:41,
from
/opt/compiler-explorer/gcc-7.1.0/include/c++/7.1.0/ios:42,
from
/opt/compiler-explorer/gcc-7.1.0/include/c++/7.1.0/istream:38,
from
/opt/compiler-explorer/gcc-7.1.0/include/c++/7.1.0/sstream:38,
from <source>:1:
/opt/compiler-explorer/gcc-7.1.0/include/c++/7.1.0/bits/basic_string.h:588:9:
note: candidate: template<class _InputIterator, class>
std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>::basic_string(_InputIterator, _InputIterator, const _Alloc&)
basic_string(_InputIterator __beg, _InputIterator __end,
^~~~~~~~~~~~
/opt/compiler-explorer/gcc-7.1.0/include/c++/7.1.0/bits/basic_string.h:588:9:
note: template argument deduction/substitution failed:
<source>:24:76: note: candidate expects 3 arguments, 1 provided
std::string s{/*static_cast<my_stream&>*/(my_stream{} << "hello world")};
^
In file included from
/opt/compiler-explorer/gcc-7.1.0/include/c++/7.1.0/string:52:0,
from
/opt/compiler-explorer/gcc-7.1.0/include/c++/7.1.0/bits/locale_classes.h:40,
from
/opt/compiler-explorer/gcc-7.1.0/include/c++/7.1.0/bits/ios_base.h:41,
from
/opt/compiler-explorer/gcc-7.1.0/include/c++/7.1.0/ios:42,
from
/opt/compiler-explorer/gcc-7.1.0/include/c++/7.1.0/istream:38,
from
/opt/compiler-explorer/gcc-7.1.0/include/c++/7.1.0/sstream:38,
from <source>:1:
/opt/compiler-explorer/gcc-7.1.0/include/c++/7.1.0/bits/basic_string.h:550:7:
note: candidate: std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>::basic_string(std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&&,
const _Alloc&) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc =
std::allocator<char>]
basic_string(basic_string&& __str, const _Alloc& __a)
^~~~~~~~~~~~
/opt/compiler-explorer/gcc-7.1.0/include/c++/7.1.0/bits/basic_string.h:550:7:
note: candidate expects 2 arguments, 1 provided
/opt/compiler-explorer/gcc-7.1.0/include/c++/7.1.0/bits/basic_string.h:546:7:
note: candidate: std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>::basic_string(const std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>&, const _Alloc&) [with _CharT = char; _Traits = std::char_traits<char>;
_Alloc = std::allocator<char>]
basic_string(const basic_string& __str, const _Alloc& __a)
^~~~~~~~~~~~
/opt/compiler-explorer/gcc-7.1.0/include/c++/7.1.0/bits/basic_string.h:546:7:
note: candidate expects 2 arguments, 1 provided
/opt/compiler-explorer/gcc-7.1.0/include/c++/7.1.0/bits/basic_string.h:542:7:
note: candidate: std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>::basic_string(std::initializer_list<_Tp>, const _Alloc&) [with _CharT =
char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>]
basic_string(initializer_list<_CharT> __l, const _Alloc& __a = _Alloc())
^~~~~~~~~~~~
/opt/compiler-explorer/gcc-7.1.0/include/c++/7.1.0/bits/basic_string.h:542:7:
note: no known conversion for argument 1 from 'std::basic_ostream<char>' to
'std::initializer_list<char>'
/opt/compiler-explorer/gcc-7.1.0/include/c++/7.1.0/bits/basic_string.h:515:7:
note: candidate: std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>::basic_string(std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&&)
[with _CharT = char; _Traits = std::char_traits<char>; _Alloc =
std::allocator<char>]
basic_string(basic_string&& __str) noexcept
^~~~~~~~~~~~
/opt/compiler-explorer/gcc-7.1.0/include/c++/7.1.0/bits/basic_string.h:515:7:
note: no known conversion for argument 1 from 'std::basic_ostream<char>' to
'std::__cxx11::basic_string<char>&&'
/opt/compiler-explorer/gcc-7.1.0/include/c++/7.1.0/bits/basic_string.h:503:7:
note: candidate: std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>::basic_string(std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>::size_type, _CharT, const _Alloc&) [with _CharT = char; _Traits =
std::char_traits<char>; _Alloc = std::allocator<char>;
std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::size_type = long unsigned
int]
basic_string(size_type __n, _CharT __c, const _Alloc& __a = _Alloc())
^~~~~~~~~~~~
/opt/compiler-explorer/gcc-7.1.0/include/c++/7.1.0/bits/basic_string.h:503:7:
note: candidate expects 3 arguments, 1 provided
/opt/compiler-explorer/gcc-7.1.0/include/c++/7.1.0/bits/basic_string.h:493:7:
note: candidate: std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>::basic_string(const _CharT*, const _Alloc&) [with _CharT = char;
_Traits = std::char_traits<char>; _Alloc = std::allocator<char>]
basic_string(const _CharT* __s, const _Alloc& __a = _Alloc())
^~~~~~~~~~~~
/opt/compiler-explorer/gcc-7.1.0/include/c++/7.1.0/bits/basic_string.h:493:7:
note: no known conversion for argument 1 from 'std::basic_ostream<char>' to
'const char*'
/opt/compiler-explorer/gcc-7.1.0/include/c++/7.1.0/bits/basic_string.h:483:7:
note: candidate: std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>::basic_string(const _CharT*, std::__cxx11::basic_string<_CharT,
_Traits, _Alloc>::size_type, const _Alloc&) [with _CharT = char; _Traits =
std::char_traits<char>; _Alloc = std::allocator<char>;
std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::size_type = long unsigned
int]
basic_string(const _CharT* __s, size_type __n,
^~~~~~~~~~~~
/opt/compiler-explorer/gcc-7.1.0/include/c++/7.1.0/bits/basic_string.h:483:7:
note: candidate expects 3 arguments, 1 provided
/opt/compiler-explorer/gcc-7.1.0/include/c++/7.1.0/bits/basic_string.h:465:7:
note: candidate: std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>::basic_string(const std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>&, std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::size_type,
std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::size_type, const _Alloc&)
[with _CharT = char; _Traits = std::char_traits<char>; _Alloc =
std::allocator<char>; std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>::size_type = long unsigned int]
basic_string(const basic_string& __str, size_type __pos,
^~~~~~~~~~~~
/opt/compiler-explorer/gcc-7.1.0/include/c++/7.1.0/bits/basic_string.h:465:7:
note: candidate expects 4 arguments, 1 provided
/opt/compiler-explorer/gcc-7.1.0/include/c++/7.1.0/bits/basic_string.h:449:7:
note: candidate: std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>::basic_string(const std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>&, std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::size_type,
std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::size_type) [with _CharT =
char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>;
std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::size_type = long unsigned
int]
basic_string(const basic_string& __str, size_type __pos,
^~~~~~~~~~~~
/opt/compiler-explorer/gcc-7.1.0/include/c++/7.1.0/bits/basic_string.h:449:7:
note: candidate expects 3 arguments, 1 provided
/opt/compiler-explorer/gcc-7.1.0/include/c++/7.1.0/bits/basic_string.h:434:7:
note: candidate: std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>::basic_string(const std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>&, std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::size_type, const
_Alloc&) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc =
std::allocator<char>; std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>::size_type = long unsigned int]
basic_string(const basic_string& __str, size_type __pos,
^~~~~~~~~~~~
/opt/compiler-explorer/gcc-7.1.0/include/c++/7.1.0/bits/basic_string.h:434:7:
note: candidate expects 3 arguments, 1 provided
/opt/compiler-explorer/gcc-7.1.0/include/c++/7.1.0/bits/basic_string.h:421:7:
note: candidate: std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>::basic_string(const std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>&) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc =
std::allocator<char>]
basic_string(const basic_string& __str)
^~~~~~~~~~~~
/opt/compiler-explorer/gcc-7.1.0/include/c++/7.1.0/bits/basic_string.h:421:7:
note: no known conversion for argument 1 from 'std::basic_ostream<char>' to
'const std::__cxx11::basic_string<char>&'
/opt/compiler-explorer/gcc-7.1.0/include/c++/7.1.0/bits/basic_string.h:413:7:
note: candidate: std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>::basic_string(const _Alloc&) [with _CharT = char; _Traits =
std::char_traits<char>; _Alloc = std::allocator<char>]
basic_string(const _Alloc& __a) _GLIBCXX_NOEXCEPT
^~~~~~~~~~~~
/opt/compiler-explorer/gcc-7.1.0/include/c++/7.1.0/bits/basic_string.h:413:7:
note: no known conversion for argument 1 from 'std::basic_ostream<char>' to
'const std::allocator<char>&'
/opt/compiler-explorer/gcc-7.1.0/include/c++/7.1.0/bits/basic_string.h:404:7:
note: candidate: std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>::basic_string() [with _CharT = char; _Traits = std::char_traits<char>;
_Alloc = std::allocator<char>]
basic_string()
^~~~~~~~~~~~
/opt/compiler-explorer/gcc-7.1.0/include/c++/7.1.0/bits/basic_string.h:404:7:
note: candidate expects 0 arguments, 1 provided
Compiler exited with result code 1
