/in/foo.cc: In function 'int integer(int, int)':
/in/foo.cc:7:40: error: no matching function for call to 'std::__cxx11::basic_string<char>::basic_string(int&)'
  int len=sizeof(static_cast<string>(num))/sizeof(int);//取数值位数
                                        ^
In file included from /usr/include/c++/6/string:52:0,
                 from /usr/include/c++/6/bits/locale_classes.h:40,
                 from /usr/include/c++/6/bits/ios_base.h:41,
                 from /usr/include/c++/6/ios:42,
                 from /usr/include/c++/6/ostream:38,
                 from /usr/include/c++/6/iostream:39,
                 from /in/foo.cc:2:
/usr/include/c++/6/bits/basic_string.h:549:9: 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,
         ^~~~~~~~~~~~
/usr/include/c++/6/bits/basic_string.h:549:9: note:   template argument deduction/substitution failed:
/in/foo.cc:7:40: note:   candidate expects 3 arguments, 1 provided
  int len=sizeof(static_cast<string>(num))/sizeof(int);//取数值位数
                                        ^
In file included from /usr/include/c++/6/string:52:0,
                 from /usr/include/c++/6/bits/locale_classes.h:40,
                 from /usr/include/c++/6/bits/ios_base.h:41,
                 from /usr/include/c++/6/ios:42,
                 from /usr/include/c++/6/ostream:38,
                 from /usr/include/c++/6/iostream:39,
                 from /in/foo.cc:2:
/usr/include/c++/6/bits/basic_string.h:511:7: 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)
       ^~~~~~~~~~~~
/usr/include/c++/6/bits/basic_string.h:511:7: note:   candidate expects 2 arguments, 1 provided
/usr/include/c++/6/bits/basic_string.h:507:7: 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)
       ^~~~~~~~~~~~
/usr/include/c++/6/bits/basic_string.h:507:7: note:   candidate expects 2 arguments, 1 provided
/usr/include/c++/6/bits/basic_string.h:503:7: 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())
       ^~~~~~~~~~~~
/usr/include/c++/6/bits/basic_string.h:503:7: note:   no known conversion for argument 1 from 'int' to 'std::initializer_list<char>'
/usr/include/c++/6/bits/basic_string.h:476:7: 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
       ^~~~~~~~~~~~
/usr/include/c++/6/bits/basic_string.h:476:7: note:   no known conversion for argument 1 from 'int' to 'std::__cxx11::basic_string<char>&&'
/usr/include/c++/6/bits/basic_string.h:464:7: 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())
       ^~~~~~~~~~~~
/usr/include/c++/6/bits/basic_string.h:464:7: note:   candidate expects 3 arguments, 1 provided
/usr/include/c++/6/bits/basic_string.h:454:7: 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>] <near match>
       basic_string(const _CharT* __s, const _Alloc& __a = _Alloc())
       ^~~~~~~~~~~~
/usr/include/c++/6/bits/basic_string.h:454:7: note:   conversion of argument 1 would be ill-formed:
/in/foo.cc:7:40: error: invalid conversion from 'int' to 'const char*' [-fpermissive]
  int len=sizeof(static_cast<string>(num))/sizeof(int);//取数值位数
                                        ^
In file included from /usr/include/c++/6/string:52:0,
                 from /usr/include/c++/6/bits/locale_classes.h:40,
                 from /usr/include/c++/6/bits/ios_base.h:41,
                 from /usr/include/c++/6/ios:42,
                 from /usr/include/c++/6/ostream:38,
                 from /usr/include/c++/6/iostream:39,
                 from /in/foo.cc:2:
/usr/include/c++/6/bits/basic_string.h:444:7: 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,
       ^~~~~~~~~~~~
/usr/include/c++/6/bits/basic_string.h:444:7: note:   candidate expects 3 arguments, 1 provided
/usr/include/c++/6/bits/basic_string.h:426:7: 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,
       ^~~~~~~~~~~~
/usr/include/c++/6/bits/basic_string.h:426:7: note:   candidate expects 4 arguments, 1 provided
/usr/include/c++/6/bits/basic_string.h:410:7: 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,
       ^~~~~~~~~~~~
/usr/include/c++/6/bits/basic_string.h:410:7: note:   candidate expects 3 arguments, 1 provided
/usr/include/c++/6/bits/basic_string.h:397:7: 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)
       ^~~~~~~~~~~~
/usr/include/c++/6/bits/basic_string.h:397:7: note:   no known conversion for argument 1 from 'int' to 'const std::__cxx11::basic_string<char>&'
/usr/include/c++/6/bits/basic_string.h:389:7: 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
       ^~~~~~~~~~~~
/usr/include/c++/6/bits/basic_string.h:389:7: note:   no known conversion for argument 1 from 'int' to 'const std::allocator<char>&'
/usr/include/c++/6/bits/basic_string.h:380:7: note: candidate: std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::basic_string() [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>]
       basic_st