为什么我不能从C中的单个char构造一个std :: string？

#include <string>

int main()
{
    char c = 'a';
    std::string s(c);
    return 0;
}

在g中,我得到这么多错误,

foo.cpp: In function 'int main()':
foo.cpp:6:20: error: no matching function for call to 'std::__cxx11::basic_strin
g<char>::basic_string(char&)'
     std::string s(c);
                    ^
In file included from i:/Qtandroid/Qt5.7.0/Tools/mingw530_32/i686-w64-mingw32/in
clude/c++/string:52:0,from foo.cpp:1:
i:/Qtandroid/Qt5.7.0/Tools/mingw530_32/i686-w64-mingw32/include/c++/bits/basic_s
tring.h:535:9: note: candidate: template<class _InputIterator> std::__cxx11::bas
ic_string<_CharT,_Traits,_Alloc>::basic_string(_InputIterator,_InputIterator,const _Alloc&)
         basic_string(_InputIterator __beg,_InputIterator __end,^
i:/Qtandroid/Qt5.7.0/Tools/mingw530_32/i686-w64-mingw32/include/c++/bits/basic_s
tring.h:535:9: note:   template argument deduction/substitution failed:
foo.cpp:6:20: note:   candidate expects 3 arguments,1 provided
     std::string s(c);
                    ^
In file included from i:/Qtandroid/Qt5.7.0/Tools/mingw530_32/i686-w64-mingw32/in
clude/c++/string:52:0,from foo.cpp:1:
i:/Qtandroid/Qt5.7.0/Tools/mingw530_32/i686-w64-mingw32/include/c++/bits/basic_s
tring.h:465:7: note: candidate: std::__cxx11::basic_string<_CharT,_All
oc>::basic_string(std::__cxx11::basic_string<_CharT,_Alloc>::size_type,_CharT,const _Alloc&) [with _CharT = char; _Traits = std::char_traits<char>;
_Alloc = std::allocator<char>; std::__cxx11::basic_string<_CharT,_Allo
c>::size_type = unsigned int]
       basic_string(size_type __n,_CharT __c,const _Alloc& __a = _Alloc())
       ^
i:/Qtandroid/Qt5.7.0/Tools/mingw530_32/i686-w64-mingw32/include/c++/bits/basic_s
tring.h:465:7: note:   candidate expects 3 arguments,1 provided
i:/Qtandroid/Qt5.7.0/Tools/mingw530_32/i686-w64-mingw32/include/c++/bits/basic_s
tring.h:455:7: note: candidate: std::__cxx11::basic_string<_CharT,_All
oc>::basic_string(const _CharT*,const _Alloc&) [with _CharT = char; _Traits = s
td::char_traits<char>; _Alloc = std::allocator<char>] <near match>
       basic_string(const _CharT* __s,const _Alloc& __a = _Alloc())
       ^
i:/Qtandroid/Qt5.7.0/Tools/mingw530_32/i686-w64-mingw32/include/c++/bits/basic_s
tring.h:455:7: note:   conversion of argument 1 would be ill-formed:
foo.cpp:6:20: error: invalid conversion from 'char' to 'const char*' [-fpermissi
ve]
     std::string s(c);
                    ^
In file included from i:/Qtandroid/Qt5.7.0/Tools/mingw530_32/i686-w64-mingw32/in
clude/c++/string:52:0,from foo.cpp:1:
i:/Qtandroid/Qt5.7.0/Tools/mingw530_32/i686-w64-mingw32/include/c++/bits/basic_s
tring.h:445:7: note: candidate: std::__cxx11::basic_string<_CharT,std::__cxx11::basic_string<_CharT,_Al
loc>::size_type,const _Alloc&) [with _CharT = char; _Traits = std::char_traits<
char>; _Alloc = std::allocator<char>; std::__cxx11::basic_string<_CharT,_Alloc>::size_type = unsigned int]
       basic_string(const _CharT* __s,size_type __n,^
i:/Qtandroid/Qt5.7.0/Tools/mingw530_32/i686-w64-mingw32/include/c++/bits/basic_s
tring.h:445:7: note:   candidate expects 3 arguments,1 provided
i:/Qtandroid/Qt5.7.0/Tools/mingw530_32/i686-w64-mingw32/include/c++/bits/basic_s
tring.h:427:7: note: candidate: std::__cxx11::basic_string<_CharT,_All
oc>::basic_string(const std::__cxx11::basic_string<_CharT,_Alloc>&,st
d::__cxx11::basic_string<_CharT,std::__cxx11::basi
c_string<_CharT,const _Alloc&) [with _CharT = char
; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>; std::__cxx11:
:basic_string<_CharT,_Alloc>::size_type = unsigned int]
       basic_string(const basic_string& __str,size_type __pos,^
i:/Qtandroid/Qt5.7.0/Tools/mingw530_32/i686-w64-mingw32/include/c++/bits/basic_s
tring.h:427:7: note:   candidate expects 4 arguments,1 provided
i:/Qtandroid/Qt5.7.0/Tools/mingw530_32/i686-w64-mingw32/include/c++/bits/basic_s
tring.h:411:7: note: candidate: std::__cxx11::basic_string<_CharT,_Alloc>::size_type) [with _CharT = char; _Traits = std
::char_traits<char>; _Alloc = std::allocator<char>; std::__cxx11::basic_string<_
CharT,^
i:/Qtandroid/Qt5.7.0/Tools/mingw530_32/i686-w64-mingw32/include/c++/bits/basic_s
tring.h:411:7: note:   candidate expects 3 arguments,1 provided
i:/Qtandroid/Qt5.7.0/Tools/mingw530_32/i686-w64-mingw32/include/c++/bits/basic_s
tring.h:399:7: note: candidate: std::__cxx11::basic_string<_CharT,_Alloc>&) [w
ith _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<cha
r>]
       basic_string(const basic_string& __str)
       ^
i:/Qtandroid/Qt5.7.0/Tools/mingw530_32/i686-w64-mingw32/include/c++/bits/basic_s
tring.h:399:7: note:   no known conversion for argument 1 from 'char' to 'const
std::__cxx11::basic_string<char>&'
i:/Qtandroid/Qt5.7.0/Tools/mingw530_32/i686-w64-mingw32/include/c++/bits/basic_s
tring.h:391:7: note: candidate: std::__cxx11::basic_string<_CharT,_All
oc>::basic_string(const _Alloc&) [with _CharT = char; _Traits = std::char_traits
<char>; _Alloc = std::allocator<char>]
       basic_string(const _Alloc& __a)
       ^
i:/Qtandroid/Qt5.7.0/Tools/mingw530_32/i686-w64-mingw32/include/c++/bits/basic_s
tring.h:391:7: note:   no known conversion for argument 1 from 'char' to 'const
std::allocator<char>&'
i:/Qtandroid/Qt5.7.0/Tools/mingw530_32/i686-w64-mingw32/include/c++/bits/basic_s
tring.h:380:7: note: candidate: std::__cxx11::basic_string<_CharT,_All
oc>::basic_string() [with _CharT = char; _Traits = std::char_traits<char>; _Allo
c = std::allocator<char>]
       basic_string()
       ^
i:/Qtandroid/Qt5.7.0/Tools/mingw530_32/i686-w64-mingw32/include/c++/bits/basic_s
tring.h:380:7: note:   candidate expects 0 arguments,1 provided

有没有理由让这个构造函数丢失.

这有效,但感觉不对,

#include <string>

int main()
{
    char c = 'a';
    std::string s;
    s += c;
    return 0;
}

任何建议,谢谢.