g++ mbox2eml.cpp

make

mbox2eml.cpp: In function 'int main(int, char**)':
mbox2eml.cpp:58:82: error: 'to_string' is not a member of 'std'
           filename = FILENAME_PREFIX + std::string(4 - (int)log10(index), '0') + std::to_string(index) + '-' + subject + FILENAME_EXTENSION;
                                                                                  ^
mbox2eml.cpp: In function 'void save(std::__cxx11::string, const string&)':
mbox2eml.cpp:81:32: error: no matching function for call to 'std::basic_fstream<char>::open(std::__cxx11::string&, const openmode&)'
   file.open(name, std::ios::out);
                                ^
In file included from mbox2eml.cpp:17:0:
/usr/include/c++/5/fstream:1001:7: note: candidate: void std::basic_fstream<_CharT, _Traits>::open(const char*, std::ios_base::openmode) [with _CharT = char; _Traits = std::char_traits<char>; std::ios_base::openmode = std::_Ios_Openmode]
       open(const char* __s,
       ^
/usr/include/c++/5/fstream:1001:7: note:   no known conversion for argument 1 from 'std::__cxx11::string {aka std::__cxx11::basic_string<char>}' to 'const char*'

$ g++ --version

g++ (Ubuntu 5.4.0-6ubuntu1~16.04.11) 5.4.0 20160609
Copyright (C) 2015 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.