做操纵器不知怎的转换流类型？

Question

我试图使用匿名ostringstream生成一个string：Use an Anonymous Stringstream to Construct a String

然而，当我使用机械臂我似乎无法编译下去：

const auto myString(static_cast<ostringstream>(ostringstream{} << setfill('!') << setw(13) << "lorem ipsum").str()); 

但是，这似乎并没有不允许even in gcc 5.1：

prog.cpp: In function int main() :
prog.cpp:8:109: error: no matching function for call to std::basic_ostringstream<char>::basic_ostringstream(std::basic_ostream<char>&)
const auto myString(static_cast<ostringstream>(ostringstream{} << setfill('!') << setw(13) << "lorem ipsum").str());


In file included from /usr/include/c++/5/iomanip:45:0,
from prog.cpp:1:
/usr/include/c++/5/sstream:582:7: note: candidate
std::basic_ostringstream<_CharT, _Traits, _Alloc>::basic_ostringstream(std::basic_ostringstream<_CharT, _Traits, _Alloc>&&) [with _CharT = char ; _Traits = std::char_traits<char> ; _Alloc = std::allocator<char> ]
basic_ostringstream(basic_ostringstream&& __rhs)

/usr/include/c++/5/sstream:582:7: note: no known conversion for argument 1 from std::basic_ostream<char> to std::basic_ostringstream<char>&&
/usr/include/c++/5/sstream:565:7: note: candidate:
std::basic_ostringstream<_CharT, _Traits, _Alloc>::basic_ostringstream(const __string_type&, std::ios_base::openmode) [with _CharT = char ; _Traits = std::char_traits<char> ; _Alloc = std::allocator<char> ; std::basic_ostringstream<_CharT, _Traits, _Alloc>::__string_type = std::basic_string<char> ; std::ios_base::openmode = std::_Ios_Openmode ]
basic_ostringstream(const __string_type& __str,

/usr/include/c++/5/sstream:565:7: note: no known conversion for argument 1 from std::basic_ostream<char> to const __string_type& {aka const std::basic_string<char>&}
/usr/include/c++/5/sstream:547:7: note: candidate:
std::basic_ostringstream<_CharT, _Traits, _Alloc>::basic_ostringstream(std::ios_base::openmode) [with _CharT = char ; _Traits = std::char_traits<char> ; _Alloc = std::allocator<char> ; std::ios_base::openmode = std::_Ios_Openmode ]
basic_ostringstream(ios_base::openmode __mode = ios_base::out)

/usr/include/c++/5/sstream:547:7: note: no known conversion for argument 1 from std::basic_ostream<char> to std::ios_base::openmode {aka std::_Ios_Openmode}

这是另一GCC流错误，或者是我在做什么实际上是非法？

Answer 1

static_cast<ostringstream>(...) 

这将着力构建从参数新ostringstream在括号，一个std::ostream&，对此有没有std::ostringstream构造。

您只想将参考转换回原始类型。使演员参考：

static_cast<ostringstream&>(...) 

然后它工作正常。

我不知道你的想法是什么，但忽略了参考，并删除操纵器，它仍然失败。