C++ STL map中的Key使用自定義類型

C++ STL 中的map容器中的元素是按照Key的升序進行排列的，所以map的Key需要使用自定義類型時，該自定義類型必須重載operator<操作符，否則會出現下面的編譯錯誤：

 

In file included from /usr/lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/string:50,
                 from /usr/lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/bits/locale_classes.h:42,
                 from /usr/lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/bits/ios_base.h:43,
                 from /usr/lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/ios:43,
                 from /usr/lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/ostream:40,
                 from /usr/lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/iostream:40,
                 from dagexing/src/online/dgxdbrpc/dgx_db.cc:2:
/usr/lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/bits/stl_function.h:
In member function 
'bool std::less<_Tp>::operator()(const _Tp&, const _Tp&) const [with _Tp = dgx_db::KtvRoomInfo]':
/usr/lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/bits/stl_map.h:449:
instantiated from '_Tp& std::map<_Key, _Tp, _Compare, _Alloc>::operator[](const _Key&) [with _Key = dgx_db::KtvRoomInfo, _Tp = dgx_db::Uint32DataType, _Compare = std::less<dgx_db::KtvRoomInfo>, _Alloc = std::allocator<std::pair<const
dgx_db::KtvRoomInfo, dgx_db::Uint32DataType> >]'
./dagexing/src/online/dgxdbrpc/dbcache.h:53: instantiated from
'int dgx_db::DbCache<KeyType, ValueType>::update(const KeyType&, ValueType&) [with KeyType = dgx_db::KtvRoomInfo, ValueType = dgx_db::Uint32DataType]'
dagexing/src/online/dgxdbrpc/dgx_db.cc:136: instantiated from here
/usr/lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/bits/stl_function.h:230:
error: no match for
'operator<' in
'__x < __y'

這個錯誤表示_Key = dgx_db::KtvRoomInfo沒有重載operator<操作符。加入下列重載函數後通過編譯

 

bool operator <
(const KtvRoomInfo& info)
const {
    if (kiid_
< info.kiid_)
      return true;
    else if
(kiid_ == info.kiid_
&& enname_ 
< info.enname_)
      return true;
    else
      return false;
  }