使用字符串作为打开文件路径的C ++ ifstream错误。

string filename: 
ifstream file(filename);

error: no matching function for call to ‘std::basic_ifstream<char, std::char_traits<char> >::basic_ifstream(std::string&)’
/usr/include/c++/4.4/fstream:454: note: candidates are: std::basic_ifstream<_CharT, _Traits>::basic_ifstream(const char*, std::_Ios_Openmode) [with _CharT = char, _Traits = std::char_traits<char>]

ifstream file(filename);

ifstream file(filename.c_str());

ifstream

const char*

string

ifstream

const char*

ifstream file(filename.c_str());