Cant insert to std::map (G++)

Question

I have a following trouble:

struct ServerPP { std::string name; int id; int expires; }; std::map<std::string, std::set<ServerPP>> RemindTable; int test(std::string email, ServerPP serv) { RemindTable[email].insert(serv); // error when compile in this row below }

Error in g++:

In file included from /usr/include/c++/4.4/string:50, from /usr/include/c++/4.4/bits/locale_classes.h:42, from /usr/include/c++/4.4/bits/ios_base.h:43, from /usr/include/c++/4.4/ios:43, from /usr/include/c++/4.4/istream:40, from /usr/include/c++/4.4/sstream:39, from stdafx.h:19, from ActiveReminder.cpp:4: /usr/include/c++/4.4/bits/stl_function.h: In member function 'bool std::less<_Tp>::operator()(const _Tp&, const _Tp&) const [with _Tp = ServerPP]': /usr/include/c++/4.4/bits/stl_tree.h:1170: instantiated from 'std::pair<typename std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::iterator, bool> std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::_M_insert_unique(const _Val&) [with _Key = ServerPP, _Val = ServerPP, _KeyOfValue = std::_Identity<ServerPP>, _Compare = std::less<ServerPP>, _Alloc = std::allocator<ServerPP>]' /usr/include/c++/4.4/bits/stl_set.h:411: instantiated from 'std::pair<typename std::_Rb_tree<_Key, _Key, std::_Identity<_Key>, _Compare, typename _Alloc::rebind<_Key>::other>::const_iterator, bool> std::set<_Key, _Compare, _Alloc>::insert(const _Key&) [with _Key = ServerPP, _Compare = std::less<ServerPP>, _Alloc = std::allocator<ServerPP>]' ActiveReminder.cpp:32: instantiated from here /usr/include/c++/4.4/bits/stl_function.h:230: error: no match for 'operator<' in '__x < __y'

How can i fix this error in G++, on windows all ok

Thanks!

Are you sure that all is okay on Windows? Try compiling code that actually calls the test() function and I think you will find an error emitted by VC++ as well. @AndyProwl's answer is spot-on. — Daniel Trebbien
– Daniel Trebbien, Commented Apr 7, 2013 at 22:54

Andy Prowl · Accepted Answer · 2015-09-11 14:47:19Z

You have to define operator < for your ServerPP data structure if you want to be able to use it in std::set. For instance:

bool operator < (ServerPP const& lhs, ServerPP const& rhs) { return (lhs.id < rhs.id); }

Alternatively, you can define your own comparator and provide its type as the second template argument to std::set:

struct serv_comp { bool operator () (ServerPP const& lhs, ServerPP const& rhs) { return (lhs.id < rhs.id); } }; std::map<std::string, std::set<ServerPP, serv_comp>> RemindTable;

Here is a live example showing the code compiling.

Could you re-upload your live example in another site? The current does not show anything.

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