I use custom stl allocator to replace std::basic_string like this: typedef std::basic_string<char, std::char_traits<char>, MySTLAllocator<char> > MyString; I want basic_ptree can use my allocator to do parse work, so I write code like this: typedef boost::property_tree::basic_ptree<MyString, MyString> PropertyTree; PropertyTree propertyTree; boost::property_tree::read_ini(std::ifstream(configFile.c_str()), propertyTree); And I met error at ini_parser.hpp, line 109~111: Str key = property_tree::detail::trim( line.substr(1, end - 1), stream.getloc()); if (local.find(key) != local.not_found()) the Str is a typedef at the begin of this function: typedef std::basic_string<Ch> Str; So my custom string can not assign to the key, so it seems can not use custom allocator at all. There have the same problem in xml_parser.